Author Topic: Injection locking the 10Mhz OCXO to external reference (upgrading a FY6600)  (Read 1950 times)

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Offline Johnny B Good

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 I'm looking for a means to add an external 10MHz reference clock input to my much upgraded FY6600 AWG that eliminates the use of a change over switch and disruption to the internal 50MHz clock generated by the 10MHz OCXO I used to upgrade the previous  50MHz 0.1ppm TCXO upgrade to the rather crappy SMD XO chip originally fitted.

 I'd originally contemplated just adding an SMA - F socket and a small change-over switch to the rear panel and hope for the best which, if the need arose, I could add some complex switching logic to minimise disruption to the 50MHz clock. However, a reference to "injection locking" in relation to a Wien Bridge oscillator gave me inspiration to delve a little deeper into the whole question of such synchronisation of oscillators. It looks an effective way to achieve my goal but duckduckgo searches failed to turn up any inspiration as to how best to "injection lock" an actual OCXO, hence this post.

 I can think of two possible ways to 'inject' the external GPSDO 10MHz reference into the OCXO. The first would be to use a small transformer to add the minimal level of 10MHz ripple to the 12v Vdd line required to drag it into lock by the 100 to 500ppt offset range with the second being application of the 10MHz reference as a ripple voltage to the Vfc control pin.

 Despite the presence of any internal decoupling components on these lines in the OCXO, given enough 'brute force and ignorance' and the susceptibility of any XO to lock onto an external signal less than 0.5ppb off frequency, I think there's every chance of this tactic working. If it does, it'll be a more elegant alternative to the socket and change-over switch method implemented by Arthur Dent in the FY6600 thread over a year ago.

 Has anyone else used this method of implementing an external 10MHz reference socket upgrade on comms and test gear? Any advice regarding pitfalls and such or suggestions to offer before I start experimenting?  :)

 In the meantime, you can gaze at a couple of image files I've attached. The collection of 10MHz OCXOs was kicked off by the 13MHz example I snagged at a recent radioham rally for just 4 quid. I used it to drive a 2 times clock multiplier to drive a divide by 13 (74193) which then drove a 5 times clock multiplier which gave me an ultra low jitter 10MHz square wave. However, in my search for a data sheet for this 5 volt part, I chanced upon a uk based ebay trader offering those 10MHz 12 volt OCXOs for just a penny shy of a fiver each. I bought three just over a week ago then another four a few days later, hence the collection. One is fitted to the AWG and, at just a fiver each, one can never have too many 10MHz OCXOs.  :)

 Now that I have a "Lifetime's Supply", I can disclose my source. He's still got "more than ten available"  >:D  I must point out that the description is less than honest in that they're ex-equipment rather than NOS (you could even see the odd through plated hole attached to a pin or two) but, at that price, one can hardly complain since they're otherwise in very good condition with plenty of tuning control range left in them.

<https://www.ebay.co.uk/itm/CQE-CRYSTAL-OSCILLATOR-10MHz-REDUCED-TO-CLEAR/253081992039?hash=item3aecdcbb67:g:x1gAAOSw~qNZh2rl>

<https://tinyurl.com/y6pl2xvk>

 The second image is my attempt at showing the effect of a couple of 10MHz Xtals on the rather jittery and saw toothed 10MHz square wave output on the PPS line of my u-blox M8N based arduino.Rpi GPS module. For a still image, it's a pretty fair representation but what you can't see is the rather toned down sawtooth correction jitter (4 per second to one every few seconds - even tens of seconds). Although not perfect, it's a surprisingly huge improvement over the raw PPS signal I'd previously been using as a frequency calibration source.

JBG
 
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Offline Johnny B Good

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 Hello all,

 I noticed that the photos did attract some interest since I posted them almost a fortnight back, despite the absence of any suggested solutions to my question being offered. Since some interest seems to have been aroused by this thread, I thought I'd report on the latest developments by way of "closure".  :)

 Several days after my initial post, I decided to do some simple tests to determine if it was even possible to 'injection lock' these CQE OCXOs and how best to achieve this goal. Sadly for me during the later phase of my tests, I managed to blow the PPS line on my precious NEO M8N based GPS module with a jolt of 12 volts. The sorry tale can be read here:-

https://www.eevblog.com/forum/projects/ublox-neo-m8n-gps-navigation-signal-amplify-module-for-arduino-rasppery-pi/msg2426871/#msg2426871

 That's not the end of the story since I bought a cheap 4 quid NEO-6M to continue my experiments. It doesn't do "10MHz" on its PPS line, just a maximum of 1KHz but this, surprisingly, still suffices as a calibration reference by which to adjust the OCXO fitted into my FY6600 function generator (and of course, can still be used to discipline an OCXO - the frequency of the PPS is pretty well immaterial to a DIY GPSDO anyway).

 This time however, I kept the GPS module well out of harms way (as I should have done with the original unit  :palm:) and set two of those OCXOs up on the breadboard as a master/slave setup to continue my aborted test program. I tried injecting the output from the "Master" into the "Slave's" Vfc pin with no joy, then into the Vref pin before trying the output pin (I didn't bother trying to inject into the 12v Vcc pin) which finally did show the desired response.

 Either the oscillator output isn't buffered at all or, (more probably) simply not very well buffered since I was able to drag the slave's frequency some +&-17ppb or more by carefully tuning the 'master' (which would likewise be dragged off frequency by the slave - the effect being mutual in this case) before 'the elastic broke' and the waveform degenerated into an amplitude modulated mix of the two OCXO outputs.

 I didn't bother to lash up an amp to buffer the master OCXO from the 'pulling effect' of the slave, which I'd expect to double the pulling range, since even a mere +/-10ppb will more than suffice to lock it to a GPSDO reference since, in this case,  I'd consider even a 1ppb error as being 'beyond the pale'.

 One thing I did notice, after removing the 100 ohm series resistor I'd originally installed from the master's output connection, was the complete nulling out when reconnecting to the slave's output pin before the signal stabilised. I need to lash up a buffer amp on the master's output to simulate the effect of a GPSDO reference source and use a Schmitt trigger buffer on the slave's output to stabilise the level being fed into the 3N502 multiply by 5 chip which has replaced the original 50MHz SMD XO so that I can feed the 'injection' signal into the slave's output pin at 3 to 6dB down to eliminate this total nulling out effect.

 Hopefully, even at some 3 to 6dB down, the master's buffered output in this test setup will still demonstrate the desired injection locking effect (and over at least a +/-10ppb range). I've obviously got a lot more testing to do but this does look a promising alternative to just simply using a change-over switch between the internal and external clock reference sources with all the pitfalls that such a scheme entails (unwanted breaks and switching transients).

 Assuming these tests verify my 'injection locking' technique, I'll have to take drive levels into account when designing the add on level limiting and buffering circuit (I think a single 74HC14 IC will suffice here) since I'm currently relying on the relatively high output impedance of the OCXO's 4Vpp sine wave output to save destructively over-driving the 3N502 multiplier which is powered off the 3.3v rail on the main board. I suspect the multiplier chip won't take so kindly to the direct output from a 74HC14 output powered from a 5 volt rail (precautions will need to be taken).

 I'll report on further progress as and when I actually make any. In the meantime, I've no further images to offer at this stage but, if a justification to include any arises later on, I can always do a brief follow up if I can't add them in a later edit.

JBG

[EDIT 2020-02-04]

 "Good news Everyone!"  :)

 After finally completing my Basic DIY GPSDO project a fortnight or so back, I was able to finally resume this frequency locking to an external 10MHz reference add on module project for my FY6600 (much to the seeming amusement of the minor deities, "Murphy" and "Sod" - at times it hadn't been so much a case of "Two steps forward, one step back." so much as more like "One step forward and two steps back."  ::) ).

 Anyway, suffice to say that I finally completed the project late this afternoon and, with the signal generator finally locked to my GPSDO 10MHz reference, I'm currently in the middle of a brief three hour experiment to determine whether or not the μHz frequency adjustment is a "Real Thing" or just a cosmetic feature of this dirt cheap signal generator.

 I've just realised in hindsight, that this is a test that could be performed without locking the sig genny to an external 10MHz reference. You set one channel to exactly 10MHz sine wave (or Sinc pulse) to use as the trigger reference and simply observe the second channel set to generate a Sinc pulse with a 1μHz offset dialled in.

 Sine based waveforms (and possibly including the triangle waveform) will average out the 4ns jitter inherent to the DDS technology used in this sig genny when not using the "magic" frequencies based on integer division of its 250MHz DAC sampling clock frequency (50, 25 and 12.5 MHz for examples - running with a 1μHz offset is never going to be any such "magic" frequency anyway - "Close, but no cigar." being the applicable phrase in this case). You can still see the effect of (in this case) the 4ns p2p jitter (see attached 'scope screen shots) but it's easier to assess the average mid point along the X axis than when using square wave forms. Note: the second image was captured just 5 hours after starting the test run when the peak had been centred just 0.5ns to the left of the trigger marker line.

 To be able to observe a relative drift of just 1ns (about the minimum required for an initial assessment) requires a run time of 2 hours and 47 minutes alone which puts this endeavour into the class of "Watching paint dry". A more complete experiment to observe a half cycle drift (50ns at 10MHz) requires a run time of 138 hours and 53 minutes ( The best part of a week!) which puts it in the category of "Watching paint peel."

 Some 2 1/2 hours in and it seems to have shifted by the anticipated 1ns but I discovered about an hour ago whilst tilting the sig genny to observe the gravitation effect on my injection locking module's attempts at holding the internal OCXO on frequency (and in phase) that the T adapter connection to the scope's CH2 BNC, which is monitoring the GPSDO 10MHz reference signal, was less than stellar in that it could introduce a variation of circa 1ns depending on the angle of dangle of the cables. However, an overnight run should answer the question of "Real or Cosmetic?".  :)

 I'll post a more detailed report in the next few days once I've gotten over my surprise at actually completing not just one project but two! The GPSDO project took me just over a year to complete and this frequency injection locking project just a mere eight months!  ::)

[END_EDIT]

« Last Edit: May 25, 2020, 07:53:46 pm by Johnny B Good »
 
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Offline Johnny B Good

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As promised in my latest (now 6 day old) edit of the previous posting I'd made on the 31st of May last year, I'm providing a detailed update on the culmination of this injection locking project.
 
Regarding the cheap NEO-6M I referenced in that May 2019 post, that proved to be a complete waste of 4 quid as far as my plans for building a simple PLL based GPSDO were concerned.

Programming the PPS line to output 50% duty cycle 1ms pulses so as to run the Phase Detector at a less glacial rate than 1Hz failed because it suffered from an entirely unexpected behaviour whereby at the halfway point in a 10 to 20 minute or so cycle time (which seemed dependant on how far from exactidue the on-board 48MHz XO happened to be), the nicely square shaped pulses would start slimming down until they finally disappeared up their own fundament for a split second before reincarnating as full fat 50% duty cycle pulses once more for another turn around the block.

I suffered almost a whole week's worth of frustration in trying to get my PLL to lock the OCXO to the GPS module's 1KHz "square" wave output before it finally occurred to me to monitor exactly what was being presented to the phase detector inputs. Even then, it didn't become immediately apparent until I'd kept a watchful eye on the 'scope traces for over ten minutes.

The problem proved intractable. My work around of using the class II phase detector in an ancient 4046 I'd been testing with and programming the narrowest possible 1μs wide pulse so as to restrict the funny business of it disappearing up its own fundament to the last split second of a 10 to 20 minute cycle failed to dilute the effect in a vast ocean of time sufficiently to avoid corrupting the PLL process.
 
Having tried a long shot at resolving this issue, I then had no choice but to order a cheap NEO-M8N module to replace the very peculiar NEO-6M I'd chanced 4 quid on before I could resume testing of my basic GPSDO project and transfer it from the solderless breadboard stage onto the vero-board inside of an actual project box stage. Thankfully, this 15 quid purchase arrived just a week later. It was a 'fake' (no flash - but a CR2032 coin cell overcomes the half hour data retention time limit). Fake or not, in this case it really didn't matter and I was able cobble a working GPSDO together on my breadboard test setup.
 
In the end, I used an even cheaper 8 quid 'fake' M8N to complete the GPSDO project since the 15 quid fake was around 10dB 'deafer' than the original genuine module I'd blown out the PPS line on and this second even cheaper fake was only some 2 or 3dB down on the original (I suspect this merely lacks the flash rather than the LNA and SAW filter components as well). My external GPS antenna has a direct view of a Cellphone tower that's only 103 metres away which can desense these GPS modules by some 2 to 6dB as evidenced by a whole constellation's worth of SV signals dropping some 2 to 6dB in almost complete unison (there's usually one or two SV's that defy this desense hypothesis) each time it fires up in my direction.

Since I'm now forced to rely on Ebay and Banggood for my component supply, this adds considerable delay to any such projects, hence the rather protracted hiatus in this injection locking project of mine. I needed a working GPSDO reference before it would make any sense to resume this project once more.

Having finally commissioned a MK I GPSDO some three weeks ago (I plan on making a MK II version later in the year), I was able to turn my thoughts to designing myself a frequency locking injection module for that aforementioned FY6600 sig genny.

Now that I had a 10MHz +12dBm sine wave into 50 ohm reference that couldn't be pulled off frequency by any loads, I could finally lash up a test circuit onto a solderless breadboard with one of the half dozen CQE 10MHz OCXOs I happen to have going spare. I did try injecting into the Vref and Vfc pins but found injecting into the output pin still gave the best result.

Curiosity over the impedance my injected signal was driving into led me to run a basic impedance test on all 6 of these CQE OCXOs which ranged from a low of 75 ohms through to a high of 90 ohms. A lot lower than I had expected but not the 50 ohm impedance so typically quoted for many sine wave output OCXOs. Until that point in time, it had never occurred to me to test the output impedance of these OCXOs - I'd just assumed it wouldn't really matter a whole lot in practice.

In all my (inexcusable) ignorance, I hadn't realised just how much of a beating my precious 3N502 clock multiplier chip had been taking when the sig genny was powered down with the OCXO left running from its own 12v psu kept live whilst the generator remained plugged into a live mains outlet. The injection locking module now has the honour of guarding my precious 3N502 (precious 'cos they cost something like a fiver a pop versus the ten for a quid 74HC14 chips) from this onslaught.

At least if the 74HC14 in the injection locking module succumbs to this abuse, I still have two unused inverters going spare as substitutes (if that ever happens I'll add a 100 ohm resistor in series to reduce the input protection clamp diodes' current to a less stressful level). In any case, I'd much prefer having to replace a 10 pence part than a 5 quid one.

My hunch that a single 74HC14 IC would suffice proved correct but I did add a BC547 buffer amp between the extl 10MHz reference input BNC socket and the single inverter I was using to drive the 10.4MHz 3 pole Butterworth LPF I was using to convert the square wave back into a reasonable facsimile of a sine wave at a well defined voltage level to inject into the OCXO's output pin which itself was driving another inverter biassed to its mid-point to generate a reliable square wave immune to the inevitable variations in signal level arising out of injecting the external reference at some 3 to 6dB down on the OCXO's output.

At this stage of the breadboard testing phase, I needed to know how much level of injection signal I could apply before the risk of completely nulling out the oscillator's output voltage (quite possibly completely stalling the oscillator which is even worse) and how reliably the inverter gate could convert it back to a well defined square wave voltage to drive the 3N502 multiplier I was using to recreate the original 50MHz clock from the 10MHz OCXO which had replaced the cheap and nasty 50MHz XO chip originally used in the Feeltech design.

Being on soldelress breadboard, there was significant 'ground bounce' both within the circuitry and on the 'scope probe connections to muddy the waters but I did persevere with my testing until I felt I was ready to commit it to a copper ground plane with the hex schmitt inverter mounted 'dead bug' style.

Knowing I'd have to reduce the level coming out of the LPF to eliminate the risk of completely killing the OCXO's output signal, I designed the filter for 300 ohm impedance and put a 300 ohm resistor in series between the output of the inverter and the filter's input with a 100 ohm resistor in  series in the feed to the OCXO's output pin.

This didn't work out quite as well as I'd hoped so, just on a hunch alone, I put a 10MHz crystal in series with the filter's output which improved the pulling range but I discovered the effect was very assymetric in that whilst I could drag the frequency down by over 30ppb, I could rarely pull it up by more than 5ppb with any of the six OCXOs I tried. I figured the ground bounce effect from the solderless breadboard construction was aggravating this problem so it wasn't until I started testing the final module built onto the copper groundplane that I finally figured out a solution.

Basically, I had overlooked the fact that the series resonant mode of any quartz crystal resonator that this simple filtering effect depended upon was just slightly lower than the marked frequency (perhaps just a KHz or two in this case), requiring the use a low value capacitor in series in order to shift Rs up to 10MHz exactly. I had a vague notion that something in the range of 15 to 30pF would be required so wired a 45pF compression trimmer in series with the crystal and placed this across the 10MHz feed to the 'scope and tuned the trimmer for minimum signal voltage.

Surprisingly, this test worked even better than just shorting out the half metre stub of croc clip ended BNC cable I was using for the test connection. Even more encouraging was the fact that the LC meter showed a value of 26.6pF which closely matched the 26.4pF reading from one of two or three 27pF caps I'd sampled. With the chosen 27pF cap in series (and the 100 ohm resistor now permanently removed), the assymetric effect was more than amply reduced for my purpose (a desired requirement to reliably pull the OCXO a minimum of +/-10ppb from its nominal frequency).

It has now occurred to me that a properly trimmed 10MHz quartz crystal resonator is probably all that's required to filter the inverter's output, making that 3 pole Butterworth LPF redundent (or at least replaceable with a simple RC LPF). However, by that stage, I hadn't wanted to risk upsetting what may have been a fortuitously arrived at solution and add more delay to the project.

I still have a spare 10MHz crystal and a bunch of OCXOs to experiment with at my leisure to see whether I can trim the fat off any MK II injection locking module designs. All this complexity might beg the question as to the need for such but as I've already mentioned, my concern is to avoid gross disruption to the signal generator's main clock supply which I fear could crash critical processes within the FPGA logic.

Since I need to limit the level of injection into the OCXO's output to avoid this situation and only inject another sine wave so the only distorting effect is that of amplitude ripple within limits that will allow the schmitt trigger inverter to reliably convert it to a 3v logic level without missing a single beat, I need to take a sine or square wave 10MHz reference input, convert it to a well defined 5v logic level square wave to drive a filter that outputs a reasonable facsimile of a likewise well defined level of sine wave to inject into the OCXO's output without risk of disruption to the feed to the inverter which drives the input of an attenuator network feeding the 3N502 on the main board with the required 3v logic level clock pulses, hence this "complicated" solution. My fears may be unfounded but my previous experience with a 50MHz TCXO module would suggest otherwise.

The copper groundplane mentioned above is actually an 8mm micro-bore copper pipe slit and flattened out into a 3 inch long 1 inch wide sheet which I bent into a tall L shape to act as the module's chassis held onto the back panel of the sig generator by the BNC connector. Whilst this offered a neat solution (groundplane and chassis mount all in one), it did prove a bit of a pig when it came to soldering the ground connections.

Indeed, it led to the ruination of two of the only three push-button switches that I had in my stock suited to this task which I had attempted to solder down to the 'chassis' for use as a term/thru option switch and some (fortunately repairable) damage to the last of these switches before I realised the plastic parts just couldn't tolerate soldering temperatures being applied to their metal bodies for more than a few seconds at a time. This was one example of "One step forward, two steps back." mentioned in my edit.

I did figure out a way round this problem, suffice to say that once I'd mounted the one surviving switch, I kept a short length of brass bar clamped underneath the switch location with a pair of molegrips for the rest of the build to limit the temperature rise whilst soldering the remaining groundplane component connections. This also provided a convenient means of holding it steady in a small vice clamped to the workbench for the remaining build time.

I'd initially considered mounting all of this extra circuitry onto the OCXO board itself until I realised the problems it would present to the switchable termination circuit I wanted to include to provide maximum flexibility in regard of my 10MHz lab reference feed options. Also, I was a little reluctant to pull the existing OCXO board apart for a major rebuild. Going the separate sychronising module route meant I merely had to intercept the existing OCXO coaxial feeder cable to the mainboard's original XO chip location (now occupied by the 3N502 multiplier chip).
 
I was simply going to chop into the existing co-ax feed between the OCXO module and the mainboard and solder a couple of SMA male plugs onto the cut ends which would plug into the SMA F sockets I'd elected to use on the synchronising module. I cut the cable but after all the faff of soldering a plug onto the cable coming off the mainboard, I decided it would be easier to solder an SMA socket onto the through plated hole perf board I'd built the OCXO module onto and use a handy 15cm straight to angled male to male SMA patch lead for this connection.

Remarkably, these modifications to the OCXO module had seemingly little to no effect on its calibration setting other than, inevitably for an entirely anticipated modest amount of retrace (less than half a ppb's worth at most).
 
A star feed distribution from a multi-channel amplifier is the ideal solution for such distribution but my GPSDO only sports a single output port requiring the addition of a distribution amplifier at a later date. Whilst the FY6600 is currently the only piece of lab kit with such an Extl 10MHz reference input right now, I didn't want to forego the through/term option's flexibility that would allow me to daisychain the 10MHz reference feed onto other kit if needed.

Even if I had a 4 way distribution amp and cables, it could still prove a handy feature when adding a fifth item of kit that could also benefit from such a reference source. If a job's worth doing, then (in general) it's worth doing properly as far as I'm concerned.

Before installing the module, I took the precaution of running a few tests which, contrary to some (well, a lot) of my previous projects, failed to reveal any show stopping issues from wiring errors and solder blob short circuits (Murphy must have been taking a break from his usual fun 'n' games activities that day). Testing the frequency bending limits showed that I still had good margins of stability to at least +12ppb and to -25ppb (the assymetry hadn't entirely disappeared but it was muted enough for my purpose).

Satisfied that it was as ready as it was going to be, I then mounted it into the sig genny which involves a level of commitment since I can't solder the 51 ohm terminating resistor and the 330 ohm 'stopper' resistor connection to the buffer amp input onto the BNC centre pin until after tightening up the BNC retaining nut which can only be done by turning the whole connector using a T adapter as a 'spanner' (there simply isn't any clearance for a spanner to spin the retaining nut - just barely enough room to wedge it with a pair of long needle nose pliars).

After plugging the mains cord back in and waiting a few minutes for the OCXO to reach operating temperature (its 12v psu mains connection isn't switched), I switched the sig genny on and was rewarded with a fully functioning generator that was still within 200ppt of calibration. Connecting the external 10MHz reference dropped its voltage to half and gently dragged the 10MHz Sinc pulse back onto frequency exactly as I'd anticipated.

This was all 'fine and dandy' but it was only 0.2ppb adrift to start with, not a very demanding test. I had to check out my injection locking module's behaviour at more extreme offsets which meant applying the trimtool to 'vandalise' my previous calibration efforts of three or more months back. I was able to maladjust by a margin that comfortably exceeded my minimum of +/-10ppb (IIRC, it was something like +15 to -25 ppb before things started looking decidedly ragged but without any sign of losing lock).

I've recalibrated the sig genny's OXCO to within +/- 0.2ppb but until now it would usually vary this much each day seemingly due to changes in room temperature of around 5 to 6 deg C pk2pk despite the XO being ovenised and wrapped in a sponge rubber overcoat to both shelter it from the modest cooling air flow from a small (40mm square by 10mm deep) 5 volted 12v axial fan and reduce the OCXO's internal temperature gradients (and energy consumption - a mere 850mW now). I guess once you're into ppt territory, this is where double ovening comes into its own.
 
However, at this level of precision, this is also where the effects of gravity start to loom large. Tilting the sig genny between face down and face up (180 deg pitch change) generates a delta T of 4ns per second which is a 4 ppb change in frequency when the internal OCXO is not locked to an external reference.

Even tilting the sig genny up on its bail stand (little more than a 15 deg upward tilt) is enough to show an immediate change so it's important to choose between level or tilted orientation before attempting any recalibration of the OCXO reference. I've made use of this 'feature' in the past to temporarily compensate for the diurnal temperature variations to avoid interfering with the hard won calibration setting of the frequency trim pot.

There's a possibility that this add on module might prove to be a buffer against changes in the loading on the OCXO's output from the clock multiplier chip arising out of these daily temperature changes in the main board but it's early days and up till now, I've been observing effects only visible when locked to a GPSDO reference. Once I become bored with observing the sig genny's 10,000,000.000000Hz Sinc pulse output running slow to the tune of 1.5ns per day (equates to a loss of one second every 1.8 million years!), I'll allow it to free run in order to observe whether this (hypothesised) ambient temperature variations effect has been mitigated to any extent.

Regarding my comments in the last edit of the previous posting in relation to the question of the utility of the 1μHz resolution settings, it does seem to be a real (if ever so slightly flawed) thing. Also, it turns out that you don't need to lock the generator to a precise and stable external reference in order to observe this 1ns drift per 167 minutes. Indeed, you don't even need to upgrade the original 20ppm rated XO to run the test which is best done by setting both channels to generate a Sinc pulse at exactly 10MHz using one as a trigger reference with the other offset by 1μHz.
 
When I ran this test, the horrible 4ns random jitter completely cancelled out and I was able to more accurately observe the drift rate. With a +1μHz setting it took slightly longer than the anticipated 17 minutes to drift by 0.1ns and with a-1μHz offset, it was more like 16 minutes. The 10MHz isn't one of this generator's magical frequencies so may well be straining the accuracy limits of its DDS. I haven't tried repeating these tests at any of the magical frequencies (12.5, 25 or 50MHz) as yet but I suspect this slight error may well vanish in these test cases (and likewise when comparing the 25 or 50MHz sine output against the 10MHz GPSDO reference).

 I'll run more tests as I find the time and report any further findings here at a (possibly much) later date. In the meantime, I've attached a picture of the hand drawn circuit diagram I'd been working from. It's obviously rather scruffy but, as far as I can see, an accurate representation (for the most part) of what I put together.

 BTW, the pinout sketch of  the 1117 was added when I'd been considering it as an add-on to the OCXO board to be fed from its 12v supply. It didn't make it onto the BoM once I'd decided it was going to be a separate add on module powered directly from the main board's 5v analogue supply.

 For the benefit of anyone curious about what it was resting upon, I can reveal that it was a Kenwood TS-140S HF Transceiver that happened to be a convenient support surface nicely exposed to even daylight illumination from my office/workshop window.
 
 JBG
 
« Last Edit: March 16, 2020, 03:29:37 am by Johnny B Good »
 
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Offline Labrat101

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Hi ,
after reading this with all the time and research you put into it . Impressive. I spent , I forgot how many
hours, days, weeks . I spent getting my FY6800 cheapy . to work well. If any of us get these units to work
to Feeltech Data spec sheet which was comparable to some of the high end stuff on the market.
That's why I bought it in the first place . I just could not believe the specs over price.
I replaced the entire output op's power supply ,oxco , added heat sinks on power supplies ,etc.
There was one thing you said about the output of the oxco should be matched to the PCB you used 100ohm .. this in fact should be about 80 ohm to match the PCB's capacitance. 
I don't remember the exact details did it about 9 months ago and my memory at 67 is getting  :-// .
But I did notice but never tried the empty vref pins on the main chip . there is 4 references there and are not used I was guessing these are for injection for different levels .
The jitter I got it down to almost stable @ 20Mhz with every other square  :palm:
 But I think I will live with this as is ..
If I were to add time cost parts brain juice , coffee etc into the equation . I could Have build a Fusion Reactor  and had Free Electric .. :palm: (Murphy there is no such thing as Free anything ).
Keep Posting I really like your line of thought.

If it's Gets Hot its Working. If its Getting cold! it's your Coffee.
 

Offline Johnny B Good

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Hi ,
after reading this with all the time and research you put into it . Impressive. I spent , I forgot how many
hours, days, weeks . I spent getting my FY6800 cheapy . to work well. If any of us get these units to work
to Feeltech Data spec sheet which was comparable to some of the high end stuff on the market.
That's why I bought it in the first place . I just could not believe the specs over price.
I replaced the entire output op's power supply ,oxco , added heat sinks on power supplies ,etc.
There was one thing you said about the output of the oxco should be matched to the PCB you used 100ohm .. this in fact should be about 80 ohm to match the PCB's capacitance. 
I don't remember the exact details did it about 9 months ago and my memory at 67 is getting  :-// .
But I did notice but never tried the empty vref pins on the main chip . there is 4 references there and are not used I was guessing these are for injection for different levels .
The jitter I got it down to almost stable @ 20Mhz with every other square  :palm:
 But I think I will live with this as is ..
If I were to add time cost parts brain juice , coffee etc into the equation . I could Have build a Fusion Reactor  and had Free Electric .. :palm: (Murphy there is no such thing as Free anything ).
Keep Posting I really like your line of thought.

 Well, having recently 'celebrated' my 70th birthday, I can well appreciate your concerns over your memory. :( In this case, I think you may be confusing somebody else's contribution for mine (possibly an Arthur Dent posting, maybe?). I don't recall mentioning the need to use a 100 ohm matching resistor in my own OCXO modification. In fact, as I mentioned somewhere in this thread (see! my memory fails me even for stuff I wrote just a few weeks ago - serves me right for posting such overstuffed missives I suppose :palm:), the output impedance of my batch of OCXOs hadn't even crossed my mind until I started working on this injection locking project.

 I've since determined that they range from a low of 75 ohms to a high of 90 ohms. In this case, I needed to have some idea of what the output from my injection locking circuit would be facing in order not to overdrive the output from the OCXO. I merely want to coax it into locking to the external reference without risk of nulling it out or possibly stalling it completely (which would be even worse).

 I've deliberately avoided matching the OCXO's output impedance on the injection locking module's OCXO input specifically to facilitate the injection locking process - the short 15cm or so of RG316 is only being used as a screened feed rather than as a co-axial transmission line in this case and is short enough to present no impedance mismatch problems that would otherwise arise in metre's worth of co-axial cable at 10MHz.

 The co-ax link from the module's output feeding the clk input of the 3N502 clock multiplier is even shorter and although its clk input is a high impedance (compared to 50 ohm coax at any rate), I decided to create a 50 ohm attenuator network to drop the 5v TTL output to the 3.3v logic level required by the clock multiplier chip as a token gesture impedance matching exercise in honour of the use of 50 ohm coax as short a length as it was. At the very least, any reflections from the "far end" of this unterminated coaxial line will be swiftly damped.  :)

 As for the issue of the 4ns jitter on square waves in the FY6600 and 6800 models, that's not going away any time soon. You may be able to hide it from your 'scope traces by clever triggering schemes but, except for the "special magic frequencies" it's still there, nonetheless. The only reason why I even thought to try and verify the claimed μHz resolution was on account I now had sufficient frequency accuracy and stability courtesy of now being able to lock its reference to a GPSDO.

 It was only after some protracted experimentation that I finally stumbled upon the "Set both channels to the exact same frequency with a Sinc pulse waveform and offset one by just 1μHz" method and monitor their now completely jitter free 'scope traces regardless of any XO upgrade. This is a test any owner of an FY6600 or 6800, upgraded or not, can do if they have a 2CH DSO to hand (older CRO types might not have the nanosecond resolution or triggering accuracy of the more recent DSO offerings).

 It may only be of academic interest (you'd need a reference accurate and stable to one part in 10E14 for it to be any real use - even the best GPSDOs fall short of this by an order or two of magnitude  :palm:). The one thing you can say about this is that Feeltech aren't shortchanging you on frequency resolution. ::) Accuracy, yes but definitely not a lack of resolution even if you do lock it to an atomic clock based reference.  :popcorn:

 I do have more developments to report but I'll leave that for a later and more polished posting. I'm going to compose it in a text file to (hopefully) keep it rather more concise than my more usual postings of late.

JBG
« Last Edit: May 09, 2020, 12:52:41 am by Johnny B Good »
 

Offline Labrat101

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 I totally agree .
 I think that we have both too much time to waste . But what the Heck ..
I love solving a good problem .
I believe that most of the problems lies in the filter stage after the Dac's 2 Iouts  pins 21/22
This is a stereo filter and there seems to be cross talk there I can see it on my scope.
not sure if its pore chokes or a screening problem or both .
Both sides of the filter are symmetrical Except where the DC offset is connected at the end of L31 / L33 which could be a good place to pick up noise from the OP amp IC5 .
 
I will look into this and see . .  :popcorn:

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Offline Johnny B Good

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 I'm now happy to report on the latest progress and my observations with regard to injection locking my OCXO upgraded FY6600 signal generator to an external 10MHz GPSDO source.
 
 Please note that this technique works best with unbuffered sine wave output OCXOs (and possibly the variants described as "quasi sine wave"). Those types described as having a cmos level square wave output with a duty cycle of 45 to 55 percent will be harder to influence, if at all.
 
 I haven't tested with this or the even cheaper TCXO type so can't say what the outcome would be. It's just possible it might work over a more restricted range with the OCXO type and just possibly over an even wider range with some TCXO types. Avoiding unintended injection locking usually requires careful consideration of the circuit layout so, who knows?

 One might be tempted to ask why the best quality sine wave output OCXOs don't normally incorporate their own buffer amp to minimise the effect of loading on their frequency stability. The short answer is that the additional power consumption and any noise and distortion introduced by such a buffer amp is likely to compromise the phase noise performance as well as trim a few degrees off the upper ambient temperature limit. The OCXO manufacturer would rather leave the issue of buffering to the designer of whatever their OCXOs are going to be used in as in "It's not our problem". In my case, this lack of 'buffering against external influences' has been of real benefit to this enterprise.

 Having disposed of the possible snags for anyone else who may fancy the idea of locking their FY6*00 series generator to an external 10MHz reference rather than simply switch from internal to external clock references (there is a major advantage which I'll describe presently), I can now describe the subsequent thoughts and ideas I have since had in regard of the finer details of the injection locking module's circuit.

 First off, the residual asymmetry of the adjustment range, I now realise, was on account my select on test 27pF series tuning capacitor wasn't exactly right for the job - it was 'close, but no cigar'. I still haven't replaced it with a suitable trimmer cap but it is on my 'To Do List'.

 I discovered this particular snag of using a select on test component in place of a trimmable in place component when I was looking to cure the horrendous jitter noise coming out of my homebrewed GPSDO by adding a single 10.000MHz  HC-49S crystal and 25pF trimmer in series with the LPF output and its connection to the co-ax feeding the BNC reference output socket. This made a vast improvement in my 10MHz reference frequency's quality which had been the major cause for the apparent 2.5ns Pk-Pk jitter in the signal generator's waveform trace when triggering the 'scope from this reference.

 It's true that the signal generator imposes some level of jitter on its SinC waveform but it's nowhere near as bad as my triggering from my GPSDO's output had implied. In fact, the amount of jitter appears to be around the 300ps Pk-Pk mark regardless of whether it was locked to the GPSDO reference or simply running free, significantly better than that of the pulse and square wave's 4ns jitter. IOW, injection locking rather than switching over to an external reference provides immunity to any noise and jitter in the reference being used.

  In case you're wondering how I managed to identify the real culprit for the horrendous levels of jitter visible in the DSO screengrab I'd previously posted, I simply chose one of my six spare 12v 10MHz CQE OCXOs and set it up to provide a third reference signal for comparison.

 Normally, one wouldn't expect such high levels of noise and jitter from even a homebrewed GPSDO but in my case, I'd chosen to use a 5v 13MHz square output CQE OCXO as my tunable oscillator, doubling its frequency to 26MHz to feed a divide by 13 modulo N counter in order to provide a 2MHz (minimum frequency input) to a times five clock multiplier chip feeding three inverter gates in a 74HC14 with the outputs connected to a 150 ohm combining network to drive the modified 5 element Chebyshev LPF (and now, series xtal resonator).

 Quite frankly, considering the use of Veroboard construction, it's a wonder the output looked as good as it did until I could trigger the scope from a test signal with a low(er) level of jitter. Designing and building that GPSDO (and this injection locking module) has taught me quite a lot but this is not the place and time to discuss the lessons learned from the GPSDO project.

 This experience with the need to trim the series tuning cap in situ allowed me to conclude that replacing the 27pf series cap in my injection locking module with a 25 or 33pF trimmer to let me tune the series resonance of the crystal would allow me to eliminate the asymmetry and remove the slight phase displacement when disconnecting and reconnecting the external reference whilst the signal generator's OCXO was exactly on frequency and in phase - the rapid side step when there is a phase discrepency is expected and entirely normal behaviour in this circumstance.

 As for the idea of simplifying the LPF down to just a basic RC filter, I'm not entirely sure it wouldn't introduce the risk of unwanted 3rd overtone and associated spurious responses from the crystal.

 Unlike the parallel mode resonance and odd overtones (not to be confused with odd harmonics) relationship, the series resonant mode's overtone relationship is far closer to a harmonic relationship, making the risk of exciting such undesirable responses when driven with a square wave signal all the greater.

 The output from such logic gate drivers should be filtered with a basic RC LPF at the very least before it hits any crystal filter. I won't be rushing to remove 'surplus' elements from my existing filters in the GPSDO and the injection locking module any time soon (if ever).

 However, now that I have acquired a pack of five UK sourced 10MHz HC-45S smd crystals (a snip at just £2.88 delivered) and another pack of fifty (51 actually!) of the wire ended version from China (an even better bargain at just £3.02 delivered !!!), I'll be able to experiment to my heart's content in regard of this risk of unintended filter responses with square wave drive signals.

 It might prove to be sufficient to rely upon only a simple RC LPF, allowing me to simplify a future version of the design by doing away with the 4.6uH inductor and the 2nd 100pF capacitor. The 27pF xtal cap will eventually be replaced with a trimmer to allow me to fine tune its performance.

 Although this injection locking module is far more complex a solution than the 'obvious' socket and change-over switch, it does offer the charm of a glitchless handover between the internal and external reference clocks and the even more priceless immunity to any jitter noise in your chosen reference source.

 Reviewing my other musings, I can state that the module doesn't buffer the OCXO from temperature induced changes of loading of the 3N502 clock multiplier's input pin. The effects of diurnal temperature variations remain an ever present irritation (somewhere in the region of a 200ppt Pk-Pk variation on top of the minuscule daily ageing drift).

 Regarding the question of the slight asymmetry in drift rates with 1μHz offsets using 10MHz SinC pulse waveforms, this does indeed prove to be due to limitations of the DDS technology when using frequencies not magically related to the 250MHz sampling rate of the DACs such as 50 and 25MHz. When I tested between the GPSDO reference and either of these frequencies, the drift rate, as expected, did prove to be zero.

 Although I'd chosen to build it as a separate injection module, I would advise anyone looking to upgrade the existing on board 50MHz smd XO to an off board OCXO module to allow room for the additional components of an injection locking circuit to be added, if not initially, then perhaps at a later date. If you forego the thru/term option, the length of the cable between the rear panel Ext Ref socket and the injection locking input won't be an issue if you permanently terminate it at the OCXO end wherever you plan to shoehorn this into the box.

 I think I've managed to cover everything but if anyone has any questions, feel free to ask for clarification - I don't bite (much!).

JBG

P.S.  I've attached three DSO screen captures. The first I've attached to an earlier posting showing the horrendous jitter which originated not from the cheap FY6600 signal generator but from my cheap homebrewed GPSDO. The other two images demonstrate the effect of filtering out the worst of the jitter from my GPSDO's output by use of a simple series resonant crystal filter in the output from the LPF used to convert the 10MHz square wave into a reasonable facsimile of a sine wave before it's sent to the rear panel output socket.
 
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Offline Labrat101

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I love reading your work.
There is one thing about your injection is that you wont get a stable square below the injection
frequency .  But I assume that you have a good reason not to use lower range .
as this has been well thought out. Nice scope pics. good improvement .
 
I ran some tests though my FFT scope. With a 20MHz square @ 5volt.
there was a Lot of very high harmonics appearing that were of almost equal strength as the Base
20mhz. (our friend Mr Jitter )
So I injected in a Sine at 250Khz 1/4 Harmonic not so good
 500khz  reduced all the Harmonics to less than 5db
 1Khz    was good but had less effect . which surprised me .

I was getting a nasty harmonic up over 13db  (I did it late at night I think it was the 6th or 7th)
The 500Khz did neutralize these Harmonics.

 Did you do an FFT on your setup ?
you have the 6600 model and my 1 is the FY6800 there are slight differences . the drive op amps
and some of the board layout has changed so this might only be on my model . As we both know
no 2 seem to be the same . ie part quality and tolerances  etc.
I have been very pleased with my mod with the small caps on the op amp . which is different  to the 66 models .
But the NEC relays do seem to have a funny contact capacity not as per there Nec specs.

Can you also post your schematic I would like to see your work. 





 

« Last Edit: May 18, 2020, 07:30:14 pm by Labrat101 »
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Offline Johnny B Good

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I love reading your work.
There is one thing about your injection is that you wont get a stable square below the injection
frequency .  But I assume that you have a good reason not to use lower range .
as this has been well thought out. Nice scope pics. good improvement .

 I'm glad you appreciate my efforts (not many do  ::)).

 I don't quite understand what you're getting at with regard to getting stable square waves below the injection frequency. Are you referring to my use of the 10MHz Sinc pulse as the test waveform rather than say a square wave at 5 or 2.5MHz? I'm not quite sure why injection locking should change the behaviour of the FY6600 other than for better long term frequency stability.

 I'm using the Sinc pulse waveform simply because it shares the same freedom from the 4ns jitter as the sine waveform yet gives the steepest of rise/fall times with a nice 'sharp point' to improve definition of the transit timings when comparing frequencies on a live DSO trace. You can't see it with a 1ns/ timebase displaying a 10MHz sinc pulse but at 10ns/ timebase to show just over a full cycle, the nicely spaced single spike like pulse gives a clear indication of which way the waveform is drifting relative to the trigger point in the 10MHz sine wave reference.


I ran some tests though my FFT scope. With a 20MHz square @ 5volt.
there was a Lot of very high harmonics appearing that were of almost equal strength as the Base
20mhz. (our friend Mr Jitter )
So I injected in a Sine at 250Khz 1/4 Harmonic not so good
 500khz  reduced all the Harmonics to less than 5db
 1Khz    was good but had less effect . which surprised me .

I was getting a nasty harmonic up over 13db  (I did it late at night I think it was the 6th or 7th)
The 500Khz did neutralize these Harmonics.

 I'm afraid I'm having difficulty interpreting the above. I'm assuming you were referring to the FFT function in your DSO rather than that of a spectrum analyser (SA). You can correct me if I'm wrong but using a DSO to generate FFT spectra is very tricky to optimise as I discovered a few weeks back when analysing the ripple and noise on the GPSDO's 5 volt rail, very little of which could be blamed on my using a small DC-DC buck converter alone (no LDO and only some extra LPF filtering to reduce the ripple down to 8mV pk-pk). The noise spectra were all generated by the logic gates alone which is why I plan on rebuilding a less cluttered version dead bug style on a copper clad board using one of my spare CQE 10MHz OCXOs to eliminate all the clock multiplying and divide circuitry in the current version [see note 1 for details].

 One problem I have with those figures is the absence of any sort of reference level or, indeed, whether you meant in the case of the 500KHz example a reduction by another 5dB compared to the 250KHz example and so on. One thing I did notice when analysing the 1MHz Square wave  FFT spectrum was the rather high level of even harmonics (the odd harmonic content was just about what you'd expect). I suspect this might be down to those gain and 'offset' trimpot adjustments not being spot on. There's a youtube video demonstrating how to adjust these trimpots using a square wave test signal. I think it was using the FY6600's predecessor (essentially the same circuit but less feature rich and limited to a maximum frequency of 10MHz sine wave). However, the technique works equally well for all of Feeltech's generators.

 Frequencies in the audio range can be like the curate's egg, "Good in parts" as in a sizeable number of spot frequencies were found to be almost completely free of distortion whereas most were just meh.


Did you do an FFT on your setup ?
you have the 6600 model and my 1 is the FY6800 there are slight differences . the drive op amps
and some of the board layout has changed so this might only be on my model . As we both know
no 2 seem to be the same . ie part quality and tolerances  etc.
I have been very pleased with my mod with the small caps on the op amp . which is different  to the 66 models .
But the NEC relays do seem to have a funny contact capacity not as per there Nec specs.

Can you also post your schematic I would like to see your work.

 The only FFT facility I have is that built into the SDS1202X-E which is what I used to analyse the GPSDO 5v rail noise and the spectra of test tones on the FY6600 and the noise spectra when stressing its PSU on DC 'Waveform' at various voltage levels to get a base level for when I try powering it from noise free battery power (two 6v lantern batteries for the -12v rail and a 12AH SLA for the +12v and +5v rails) to test whether replacing the much maligned smpsu board with a "better alternative" would offer any real and worthwhile benefit. Batteries are a ripple noise free power source, as is a properly decoupled 7805 regulator.

 If a 'better PSU board' can improve the purity of its output, this battery test will prove this hypothesis beyond any shadow of doubt. Mind you, it doesn't guarantee that a replacement PSU will perform any better although a properly designed analogue PSU should get very close to the purity of battery power.

 If the battery power test does indicate that a better psu is warranted, I'll be making up a mains transformer based replacement using buck converter modules in place of the miniature space heaters we call analogue voltage regulators to see whether I can get most of the benefit touted for the good old fashioned analogue voltage regulator using buck converters which switch at much lower voltage levels (and higher frequencies) and have much tighter current loop paths to minimise RFI emissions to much less than that of a mains voltage switcher with unscreened transformer as presently graces these generators.

 Regarding your request for a circuit diagram, I presume you're referring to this injection locking module. I've already posted a photograph of the hand drawn circuit I'd been working with. You'll see the attached photo in my second reply (third posting to this topic thread) above. All the detail of the original diagram has been fully captured to the extent that it is of higher resolution than you would typically get using a photocopier.

[NOTES]

[1] It will still be using an XOR gate PLL with the classic 2 pole RC LPF as before to generate the frequency control voltage for the OCXO so will still be prey to all the limitations inherent to the GPS system itself, the bulk of which arise from the varying electron density in the ionosphere. I've just recently increased the TC of the PLL filter from 38 seconds to around 470 seconds. The first time I attempted this when I'd just built the GPSDO, I'd been forced to replace the 5.6Mohm filter resistor with lower and lower values until I was down to a mere 220K before it would finally converge on the required tuning voltage which had been oscillating rail to rail until that point.

 At some point in this process, I'd included a bias resistor to pull the tuning voltage up from the natural median point when unlocked with a 4Hz unlocked square wave programmed into the GPS module to both act as an indicator and have the PLL generate a 4 Hz signal which the filter would turn into a mid point voltage to prevent it from resting at either ground or Vcc when not locked onto enough satellite signals. This time, I re scaled the resistors, including the bias resistor by a factor of 20 and left it to warm up without the GPS antenna connected to verify that I'd set the bias to somewhere in the correct ball park to get the OCXO running within 1Hz of the 10MHz target frequency.

 After about half an hour it had come to within half a Hertz and I left it running this way for another hour or so to see where it would finish. It finally settled to within 40mHz so I plugged the antenna back in and monitored the tuning voltage which oscillated up by 300mV then down by 200mV, slowly approaching the final target voltage of 3.315v with the voltage swings slowly reducing in amplitude before finally settling to within a mV of true after about 25 minutes with the frequency excursions disappearing into the 'noise' of the GPS system.

 I had prepped it up to this crude "Hold-over" state before letting it see any satellites which may have been why I had seeming success this time, so I powered it down for half a minute to give the filter caps a chance to discharge to less than a volt without letting the OCXO get too cold and fired it up to check it could repeat this 25 minute settling down trick that had failed on my first attempt with a 470 second filter time constant all those months ago. Rather pleasingly, it got back onto frequency after another twenty minutes of the same tuning voltage oscillation behaviour, confirming that my success this time had not been a fluke.

 TBH, I was a little surprised at just how swiftly it had converged to the lock value. Including the protracted OCXO warmup time (some 5 1/2 minutes or so), it had taken some ten minutes from a cold start to reach this point with the shorter 38 second filter TC value. Considering the massive twelvefold increase in the TC, I'd been  expecting a much more protracted startup time. I'm tempted to try doubling the TC on my MK2 version to see whether this can further tame the now muted phase modulations of the MK1 in response to the ionospheric perturbations on the GPS signals.

 There is a limit to how far you can go with filtering of a basic hardware PLL before you run into stability issues, let alone the fact of the rather protracted startup times. With the current filter TC value, the 25 minutes or so startup time is still quite acceptable for something that is intended to be run 24/7 year in, year out. Doubling this up to 50 or 60 minutes still remains acceptable (just!) even if that's a rather long startup time compared to microcontroller based GPSDO solutions but at least it's some two to three times faster than a few of the earlier DIY designs had required.

 A one thousand seconds filter time constant is probably as far you can go in practice to smooth out the short term (tens of minutes) variations of the raw GPS signals. Beyond that and you're looking at a microcontroller with Kalman filtering and ageing compensated hold over algorithms to overcome the deficiencies of the GPS system itself which afflict basic PLL GPSDO designs such as my current unit.

JBG

P.S. I've attached another copy of the circuit diagram (just because I can  ;) ).
 

Offline Labrat101

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Wow ,,
First I have to  give You  A++ on this Nice Home work  ^-^.
Joking aside.
The FFT I did on my HP old but faithful CRT scope that has a dedicated FFT
Module option card.  . which works really well shows that it can go as high as 10Ghz on the scale . But I have my doughs about that being correct.

I think maybe a missed read something during the 200 pages .
Where you are actually injecting to, on your circuit drawing . very nice . :-+
  "To Clk pin of 3N502 " is this the pin on the cyclone iv chip? (PLL )
were the original ocxo connects to ?? 
The out to the 3n502 you lost me were this is exactly going.

From what I see quote me if wrong .from the drawing.
your feeding 50mhz from the original Ocxo Brd  .  to the 10mhz Xtal Butterworth filter as a mixer. 
update:::
I flicked back over your earlier post . I think I did miss something.
I remember see a photo of your board layout but I could not find it again.
as you have so many posts  ;D .
You have to publish this all in 1 manuscript . A to Z .
...
  BTW way are you a professor or a lecturer as your posts seem to be inclined
this way .. Not being rude I hope . ;)
Its just the way you explain things and your insight to electronic problems .

This is really good

I think I will look in the lab see if I have an xtal 10mhz and see if I can reproduce your injection .
Can you give me the location of this 3n502 . sorry I could not find it on the main schematics .. OK call me dumbo .

update I  was rummaging though my parts box 1 found 10mhz but i only seem to have 74hc04 which is A NOT without the  Schmitt Trigger . :(  ..  I have found a CD40106 which is about the same :)
I could not find what there Max frequency rating is . Texas mentioned 1mhz


« Last Edit: May 19, 2020, 09:40:51 pm by Labrat101 »
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Offline Johnny B Good

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 Arthur Dent explains and posted a couple of pictures very early on in the FY6600 topic thread:

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1341056/#msg1341056

 You need to read through the first 15 pages at least of this thread if you want to follow what this injection locking project has been all about (I thought you'd already read all 88 pages of it  >:D).

 I've attached an earlier version of the reverse engineered circuit schematic of the main board of the FY6600 from Der Kammi's github pages (the later version didn't show the 50MHz XO chip (QG1) in that layout). You'll find it in the lower LHS of the schematic.

 When I first upgraded the ten a penny smd XO chip to a 50MHz TCXO, I removed the original chip from the board and connected an outboard 50MHz TCXO clock module to the vacated ground and output pads. Originally, I'd intended to cannibalise the clock module for its TCXO and plant it directly in place of the original smd part using wire stilts. That idea died very soon after I took some IR temperature readings around the XO location, just 10mm away from a trio of very warm LDOs (70 deg C!!!) - the XO was showing 60 deg C. No wonder you only had to blow gently onto it to send the frequency drifting off a few tens of parts per million (in this game, 1 part per million is nothing to be proud of, indeed imho, it's more something to be ashamed of).

 What Arthur Dent had been forced to do in order to use a standard 10MHz OCXO, was to replace that crappy XO chip with a NB3N502 clock multiplier chip configured to multiply the 10MHz fed into its CLK input pin fivefold to recreate the original XO's 50MHz clock on its output pin, now soldered to the pad used by the XO chip's output pin. The same requirement also applies to the FY6800 (but not the FY6900 which already uses a 10MHz XO clock chip).

 The chip layouts don't match so the usual way of dropping the NB3N502 in as a replacement for the XO is to fit it slightly cock eyed for best grounding with a minimum of additional wire links. With care and a craft knife, it's even possible to avoid additional wire links altogether if you get the angle of misalignment just right  :) .

 It may look a little 'ugly' but we're not Feeltech pretending everything was just perfect to start with by trying to disguise the 'cover up' - the presence of a hulking great OCXO rather defeats that idea of 'tidiness'. Indeed, I rather bask in the pragmatic bodging of this modification as an FU statement to Feeltech's bean counters.

 JBG
 
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Offline Labrat101

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Hi I must admit I had not read Arthur Dent,s blog .
I thought you were joking when I saw the Name ..  :phew: .

  I read them now thanks ..
I also did some research on the cyclone chip apparently it has built in PLL pins and a whole long thing
from Intel as to use these . These Pins located on the left & Right side of the chip . DAC sides.
and a describe how to deal with Jitter. To great length.
 Just blew my Brain to much info.
      Way over my Head . and out of my field .  (this might be a good place for injection . It might involve software as well . Not Sure .. I am not into Software unless its a Blond  >:D )
 You may Well understand it .  Its in the cyclone iv documents. Many Pages ..
 It Needs some one who knows How.
This is properly why Arthur Dent came up with a simpler work around solution. 3n502 PPL chip. OK  :-+

UPDATE:
In your schematic you are using 5Mhz oc where dent use a 10Mhz .so if you use 5mhz and then
inject 10mhz into 3n502 pll chip where is the 5Mhz going to ?? because its a multiplier .
I am getting confused . His method seem logical . unless you mixed them with the 5Mhz going
direct to the output  of the PLL and the injection to pin  of the 3n502 .
Can you please include pictures of your connections . I have got lost . on your injection .
I am sure it works . and you are correct but I can't connect it to gather in my mind.
and I have read your work over several times .
So some nice photos Please .
...
another Update.
According to the Manufactures recommendations of the 3N502. Use a 20MHZ x 2.5 =50Mhz
will reduce jitter due to the 48mhz internal clock of the chip.
Or as ArtherDent had also figured out. or use 2x  3N502  .  4Mhz X 2.5 =10mhz fed into the other  PLL to give the 10mhz x 2.5 =50mhz . Which runs the PLL at its optimum .
..  So I don't Get Why you have all those really good OCXO and then use a regular 10mhz Xtal
as per your circuit diagram . Sorry . If you already had the PLL installed .
 Two of those really nice ocxo with another PLL and a Buffer chip would have sufficed . (200PPb)
 This equipment will not last 1.8million years. Maybe 15,000hrs as the life time of the smd caps.

....

  I now really starting to think this project has Gone past the specs of the Big boys equipment.
  If feelelec or feeltech was to but all this info and produce a product of $150 we would have a
 Roles Royce engine in a cheesiness case. and a bigger screen  :-+
« Last Edit: May 27, 2020, 09:25:26 pm by Labrat101 »
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Offline Johnny B Good

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 Sorry for the delay in getting back to you. I've been embroiled with a rather weird "Theremin" issue with my GPSDO these past three days which has been driving me slowly round the twist. >:(

 When I first started this GPSDO project, I was making do with 3 1/2 digit DMMs to check voltages, including, once I got the whole thing soldered down onto veroboard and nicely boxed up, the EFC voltage which had started off around the 3.28 volt mark (as much resolution as a 3 1/2 digit DMM allows at this voltage). Reading to the nearest ten millivolts just wasn't good enough so I bought myself a 10000 counts DMM earlier this year which would at least resolve the EFC voltage in 1 millivolt increments.

 Just recently, I hit upon the idea of measuring the difference between the EFC voltage, now hovering around the 3.315 volt mark, and a fresh CR2032 cell (3.334v), allowing me to monitor voltage variations in tenths of a millivolt. The lithium coin cell is a remarkably stable voltage reference all things considered, showing less than a millivolt variation day to day over the 3 or 4 deg C room temperature variations and certainly stable enough to show the minute to minute and hour to hour tuning corrections being applied to the OCXO. However, flushed with my success at wringing another digit's worth of resolution out of my cheap chinese 10000 counts DMM, I thought I'd experiment with a high precision voltage reference, aka the humble TL431 typically to be found in almost  every cheap smpsu based wallwart that's been manufactured by the billion over the past two decades.

 I managed to find one in a jar of salvaged wallwart parts. A quick breadboard test confirmed it was still working and, as the data sheets implied, with a very small tempco over the 25 to 50 deg C range. The initial accuracy wasn't an issue, I was going to include a trimpot in the feedback network to raise its natural 2.495v to exactly 3.000 volts anyway. The real concern had been over how stable it would be over the temperature range inside my GPSDO which runs some 10 or 11 degrees C above room temperature (somewhere in the region of 30 to 40 degrees C, excluding heatwave conditions (coincidentally, the flattest part of the tempco curve given in all the datasheets - it's as if they'd set it this way by design).

 Right now, the tempco is the least of my problems since I seem to have stumbled upon yet a third "Theremin Fault". Just in case you don't know what a "Theremin Fault" is, it is the situation where you can effect an undesired change in an electrical gadget just by waving your hand near to said gadget or by touching it or by connecting a cable  to it even when it's just a connection to the ground terminal of the socket in question or even just the metal housing that's supposedly screening the innards from such external influences. ::) >:( :-// :wtf: |O

 Initially, I thought it may have been instability due to lack of either a 2.2nF or smaller or a 3.3uF or larger capacitor between the anode and cathode. I'd already included a 1nF cap to start with so swapped it for a 10uF ceramic but this made no difference whatsoever even after fitting a 330 ohm resistor and 150uH inductor in series with the connection to the negative reference connection socket which had originally just simply been a ground reference point for the meter connection.

 Since there is something like 70mV pk-pk of ripple and noise on the 5 volt rail (none of it being the 1.2MHz switching of the buck converter used to supply this rail - it's all TTL loading noise with components right up to 200MHz arising out of the use of veroboard construction), I figured I might be able to minimise its effect by rewiring the power feed to a quieter pick off point (the additionally filtered feed to the OCXO and the tuning voltage buffer amp) but this also made no real difference. The only other thing I've left to try (more out of desperation) is to filter the REF terminal of the TL 431 with a couple of ceramic caps going to the anode and cathode. Hopefully, this will kill off the HF noise ingress that's presumably overloading the high gain opamp part of this bandgap reference and generating this unwanted DC voltage shift (or it may make it even more unstable).

 My very first experience of this theremin effect was, unsurprisingly, during the solderless breadboard testing phase after having tested with the 13MHz square wave output OCXO with no such issue, when I started trying out a newly acquired batch of 10MHz sine wave OCXOs. I'd only had to place my hand near the wire link from the 10MHz OCXO's output to the 74HC14 inverting buffer input to detune it. Being a temporary breadboard layout, I could accept that as simply the consequence of such construction.

 However, when I experienced my second theremin fault, it was with the initial final build on veroboard mounted inside a nice screened box just when I'd thought I'd see the last of these theremin faults. Basically, it involved the separately buffered EFC voltage which would shift depending on the length of the connecting wire going to my DMM. Initially, placing a ferrite clamp around the wire was enough to eliminate the 10 mV or so shift in the reading. The actual EFC itself wasn't being effected, just the buffered feed to the external meter test point. The more compact solution was simply to place a 10uF ceramic across the output after the 100 ohm stopper resistor I'd already included to eliminate such instability issues - clearly the stopper resistor on its own had not been enough.

 Out of curiosity, I retested this buffered EFC meter test point using my newfound extra resolution courtesy of that lithium coin cell trick to see whether this was also being effected by external connections (there seemingly hadn't been any such effect other than for my TL431 reference creating errors in the the EFC readings). Close examination, at the tenth of a millivolt resolution that my trustworthy coin cell allows, did reveal a small effect of around one twentieth of a millivolt change by placing and removing a hand on the case or by plugging the cable into the 10MHz output socket. So, there seems to still be some issue of theremin effect on the buffered EFC voltage meter test point. The actual EFC voltage is not necessarily effected in this case but it might be, it's difficult to say at this stage since the effect of a twentieth of a millivolt error is very difficult to detect on the output frequency of the GPSDO - the 1 millivolt error with the 3.000v offset reference otoh, is of rather more significance since even a 0.2mV change in tuning voltage can produce a detectable shift in frequency against the FY6600's 10MHz test reference.

 Anyway, that's the story explaining my slow response. As for your thinking that I'm using a 5MHz OCXO in my FY6600, close examination of the circuit diagram on my part suggests you had misread the "SMAf" just to the left of the OCXO box as "5MHz". I'll admit to it not being too clear but that is what it actually reads when you examine it very closely. I apologise for the confusion but that's one of the hazards of posting a picture of a hand drawn circuit diagram. The image does contain ample detail such that if you scale it to match the screen pixels, it will become obvious as to what I'd actually written on the diagram.

 Like Arthur Dent, I'm using a 10MHz OCXO to drive a 3N502 chip sat right where the original 50MHz XO chip used to be on the main board. This programmed to multiply the 10MHz up to the required 50MHz of the original XO chip it replaces, exactly as per Arthur's OXCO mod.

 Where I've differed from Arthur's mod is with regard to the way the external 10MHz 'lab reference' is used (and the powering of the OCXO modules). I've used a separate 12v half amp smpsu board which maintains power to the OCXO whilst the FY6600 is plugged into a live wall socket regardless of whether it is switched on or off on the rear panel switch whilst Arthur relies on a beefed up replacement smpsu to power his OCXO from the +12v rail only whilst the whole generator is switched on.

 He uses a simple CO switch to select between the extl socket or the internal OCXO module whereas I've elected to use a frequency injection locking module to automatically lock to an external 'Lab Reference' by the action of it being plugged into the Extl socket alone without the need to manually switch between one or the other clock frequency source. The only switch in mine is to choose through or terminated operation and is purely optional - it can be left out if deemed an unnecessary luxury where your 10MHz lab reference is distributed via a star network of feeder cables.

 You mentioned 48MHz which isn't, AFAIK, a clock frequency used anywhere inside of the FY6600. It is however, the frequency of the XO or TCXO used by the various models of u-Blox GPS modules (the M8N uses a 48MHz TCXO for example) so I'm wondering if you're getting confused with GPSDO jitter and 'sawtooth' issues in this case. BTW, I'm assuming you mean PLL in those places where you've used 'PPL'  ;)

 As for the FPGA used in these signal generators, as far as I'm concerned, that's just a 'magic black box' I'm never going to live long enough to learn how to program and therefore, no point in wasting time on its gory details when there's more than enough elsewhere in the guts of these FY6*00 generators to be put right without discovering yet more things to fix in the FPGA itself. I know my limitations, thank you very much!  ;)

 As for FeelElec making a much better version for a modest price hike, the problem is exactly where do you draw the line between quality and end price? In hindsight, it's easy enough to see where a one dollar cost increase could have provided a ten dollar price hike that their target demographic would have happily swallowed, or even a two dollar cost increase for a twenty dollar price hike. The problem is at what point do you, as a manufacturer, decide to call a halt on such 'creeping featurism' and fix your costing and pricing limits?

 Perhaps if FeelElec where to properly assess the feedback from these EEVBlog fora, they might produce a more upmarket version without any of the gross bean counteritus defects, which plagues even the latest FY6900 model, at a still affordable price. You never know but, going on their record so far, it doesn't seem all that likely. :(

JBG
« Last Edit: May 24, 2020, 02:08:33 pm by Johnny B Good »
 

Offline Labrat101

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ok
So I misread SMAf  as being 5Mhz .. Ok  SO What is a SMAf  ???.

 Also I think you need to use Tantalum caps on both sides of your 1117 .regulator .
 Ceramic capacitors do have there limits .
Also as you said your SMPS is remote and these do put out Harmonics . long wire . will pick up
stray frequencies . . 200Mhz is a harmonic ..
Sorry. it was mentioned in one of the spec sheets for the 3n502 that Curtain multiples can cause
problems .
That's why I went for 20Mhz x 2.5  as per one of the manufactures stated this ..

My friendly supplier has found me 2.  CTS 20MHZ 0.02PPb OCXO 3 volt. New old stock 2015 still sealed in the original packing .  ;D, should be arriving in the next 48hrs.. :D
Spent 4 hours building a dedicated power supply for these beasts which require 3.300 volts
to hold stable during warm up. as per spec sheet says can be up to 3.8 watts.
used all Tantalum caps and tested .. second attempt got it to less than 1% .
BTW you really need to treat your self to a good 8+ digit meter . there are some good
S/Hand out there going really reasonable price . I found a few years back GW Instek GDM 8246.
fully calibrated $120 .I have been very happy with it  its accurate to +_ 1 uv .
But I am sure there may be better. came from a local tech collage sale.

I will let you know how my project works  >:D  .. The Jitter maybe my hand shaking  :-DD




« Last Edit: May 24, 2020, 02:08:17 pm by Labrat101 »
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Offline Johnny B Good

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 Good question re the "SMAf". It's simply an SMA female socket for the short male to male 15cm SMA patch lead to plug into which links to the OCXO input SMAf socket on the injection locking module. I had originally intended to simply solder an SMAm flylead to the OCXO board but changed my mind when I realised it would be neater to simply solder an SMAf PCB mount socket to the OCXO board (I just happened to have a suitable SMAm plug ended patch cable to hand).

 As for that sketch of the 117 pin outs, I'd added that to the diagram when I'd been planning on adding the injection locking circuitry to the existing OCXO board. It became redundant when I decided to build the injection locking circuit as a separate module, powered directly from a handy 5v connection on the main board (I only had the single 12v rail available on the OCXO board itself, hence the pin out sketch for a 117-5 LDO that the original plan had called for).

 Using a 20MHz OCXO with a 3n502 multiplying it by 2.5 might allow the resulting jitter to be minimised but I don't think the minimal 20 or 40 ps of jitter makes any difference to the FPGA's performance in this application. In any case, if you wish to add an external 10MHz reference socket, it will add a little more complexity in the form of another 3n502 to multiply your 10MHz reference to the 20MHz needed to drive that on-board 3n502's clock input line. However, in this case of a very precisely fixed 10MHz frequency, you could probably double it up with a simple 'XOR gate clock doubler' tuned to give a reasonably even mark/space ratio output to reduce costs (see below).

 Still, despite all that, it could work out a cheaper solution if those 20MHz OCXOs are considerably cheaper than the more in demand 10MHz (with price premium) variety. Mind you, those 3n502 clock multiplier chips aren't particularly cheap items of inventory (circa five quid a pop - about 7 or 8 dollars each at the UK/USA exchange rate) so it might still be a 'close run thing' cost-wise.

 I'm planning on rebuilding my GPSDO 'dead bug' style on a copper clad ground plane board using one of my 12v 10MHz sine wave output OCXOs to eliminate most of the "TTL power rail hash" that's presently generated by two 3n502s, an Old Skool 74193 modulo N counter (divide by 13 stage) and a 7427 triple 3 input nor gate (to even up the resulting 8:5 ratio 2MHz to a more squarish 7:6 ratio) clock input signal to drive the final five times multiplier stage which drives the 74HC14 inverting buffer which drives the LPF converting the rather jittery 10MHz square wave into a low jitter sine wave at +11.5dBm.

 Since I'd like to hang onto the current 7 to 24 volt PSU requirement, I'll have to obtain a 5 to 12v boost converter module which will nicely eat up the 200 to 300mW savings afforded by the elimination of the four highest energy consuming of the existing total of eight ICs in the current design.

 The new layout on ground plane construction and simplified circuitry of this MK II version using a proper 10MHz sine wave output OCXO should eliminate most, if not all, of the sins of veroboard construction compounded by needlessly complex circuitry. My noise and ripple concerns over the use of a 5v buck converter to supply the 5 volt rail proved to be baseless - the minuscule level of its 1.2MHz switching operation and associated switching transients had been completely submerged by the ocean of noise generated on the power rails by the processing logic in the FFT plots I'd made of the noise and ripple on the 5v rail.

 Although the use of a boost converter means I'll have to deal with higher levels of noise and ripple on the +12v rail, I don't think this will be too difficult to tame with LPF components mounted onto an effective ground plane. The OCXO will be its only 'consumer' and I'm confident that the ripple on the 12v heater supply won't matter and the built in filtering of the LDO used to power the 14mA consumption of the oscillator itself will deal rather effectively with any 12v supply ripple anyway.

 A noteworthy side benefit of employing a 12v OCXO in this case being that I get a temperature stable reference voltage from the OCXO for free - no need for a separate TL431 voltage reference in this case to generate a more stable 3.0000v (or 4.0000v) meter test point reference connection to monitor the EFC to a resolution of 100uV with a cheap MESTEK DM91A 9999 Counts Digital Multimeter I'd purchased last July for a mere 13 quid and some pennies - I notice they've gone up in price by over two quid since then  :) .

________________________________________________________________________________________________
[EDIT 2020-05-25]

CORRECTION!!!  That price increase is actually for a Chinese supplier :wtf: The original UK based supplier has actually dropped his price down to a mere £10.58 delivered postage free to UK addresses within just 5 to 7 days of placing the order. Contrary to what I stated above, the price has actually dropped by just over two quid. :)  :palm:

 For a 9999 counts DMM, that's an absolute bargain for us Brits (almost a fiver cheaper than the slow boat from china option). Mine reads 0.4% higher than the 25 yo ex BT Fluke MMF 1A FIG 84/1 I inherited as a parting gift from my former employer way back in '92 and due its next calibration March '93. :-DD

 Although it's way past its next calibration check, it compares closely to a UNI-T UT58A. Since it remained largely unused and kept stored in an office filing cabinet for all of that time (and Fluke being Fluke), I don't doubt that it's as good a reference against which to compare that Chinese cheapy as anything else I have to hand. I did open the Mestek up to locate its calibration trimmer so I could align it to my Fluke but it simply doesn't have one!

 That's both a "Good" and a "Bad" thing - good because there's no damned cheap trimpot to introduce errors and bad because there's no simple trim tool means to recalibrate it. Presumably, it's just a question of soldering the correct value of trim resistor across one the two potentiometer arms of the high precision bandgap voltage reference circuit (wherever the heck that lives!).

 However, if consistency and stability is of over-riding importance, mine seems to possess these in abundance regardless of temperature or the state of its two AAA cell battery pack voltage right down to the low voltage warning level after some 400 plus hours of continuous use ( monitoring voltage with the auto-switch off disabled - end point cell voltage, afaicr was circa 1.1v not the industry standard 0.8 to 1 volt per cell).

 I highly recommend this as a cost effective 9999 counts DMM that's both stable and consistent and very cheap to run. The only foible being that it jumps from a plus or minus 0.3mV reading straight to zero on a slowly reducing in magnitude test voltage whether manually or automatically set to its millivolt range  :wtf:. It's a strange behaviour but at greater voltage magnitudes, it functions perfectly ok. Since I rarely want to check for voltages in the +0.2mV to -0.2mV range, I can live with this idiosyncratic behaviour. In any case, there are ways and means to get around this issue if needed. ;)

 The auto-shutoff feature can be disabled, unlike that damned UNI-T which shuts off without any warning beeps just as you're trying to record your next reading :palm: The time-out is 15 minutes with a triple warning beep a minute before it actually switches itself off with a rapid series of beeps. When the auto-shutoff is disabled, it still emits these warning beeps which can be regarded as either (or even both!) an 'annoyance' or a useful reminder feature (take your pick - glass half empty/full PoV sort of thing). Personally, I find it slightly irritating but can see the benefit of not disabling the associated warning beeps.

[END_EDIT]
=============================================================================================

 I'd like a 6.5 digit (or better) lab bench meter but at ten times the price of that 9999 counts handheld DMM for a 49999 counts bench meter, let alone the several hundred quid for a 6.5 digit model, I'll stick with my Chinese cheapy and a precision offset reference voltage source for now, thank you very much! I'll hang fire on such an expensive acquisition until I can find sufficient justification for much higher precision. Just keep in mind that I'm making do with an FY6600 signal generator and you'll understand my reluctance to splash all that cash on a "Voltmeter". ;)

 A major consideration in my choosing to use the "Five Volt" 13MHz OCXO along with all the additional complexity of converting its output to a precision 10MHz sine wave was the elimination of a +12v supply rail (besides which, I'd already proved it could be used to generate a precise 10MHz reference source - in essence, it was "Because I could." :)). The exercise did provide a valuable lesson in how not to build a GPSDO so it hadn't been a complete waste of my time. ::)

 At the time when I was first trying to verify what voltage this 13MHz OCXO had been designed to run off (I was unable to track down any data sheets for this specific model of OCXO), I didn't have a handy variable voltage lab bench supply to test with and all the evidence had suggested a very real possibility of it being a five volt part that wouldn't take at all kindly to a dose of 12 volts on its Vcc pin.

 Since it seemed to function just fine (admittedly with a rather protracted 7 or 8 minute warm up delay), I decided to 'play safe' and assume, until I could gather sufficient evidence to the contrary, that it was actually a 5 volt part and avoid the risk of releasing its 'magic smoke' before I'd gotten any use out of it (4 quid might be chump change but it's still 4 quid spent on an item that I could still experiment with using just a 5 volt supply).

 Now that I have seven in total of its 12 volt 10MHz brethren, I can now well afford to, literally blow this 4 quid investment away in a voltage probing test accident which I now have some reason to think is a risk worth taking since I have a new found suspicion that it might actually be a 12 volt part after all. Obviously, this is a test scheduled for after I've rebuilt my MK II version GPSDO. ;)

 The initial warm up current demand (280mA in the case of both the 13MHz and the 10 MHz CQE OCXOs - just one reason amongst others for my suspicion that the 13MHz unit might be a 12 volt unit after all) was the reason why I opted for a 50MHz TCXO as my very first XO upgrade (just 28mA off the 5v supply - exactly the same as the relays and my 5 volted 40mm square 12v add on cooling fan!).

 The TCXO had been a vast improvement over the original XO chip but I was never going to be able to calibrate it to stay within better than +/-30ppb of 50MHz so when I lucked out during my search for datasheets for the 13MHz OCXO by finding a cheap source of its 10MHz brethren and got hold of a life time's supply (seven in all), I changed my mind with regard to Arthur Dent's seemingly OTT OCXO upgrade and followed him down the rabbit hole. ::)

 Since I'd merely modified the original smpsu board rather than replace it with a better one, as Arthur had done with sufficient current rating on the +12v rail to power an OCXO upgrade, I had no choice but to shoehorn the innards of a Linksys 12v half amp smpsu wallwart into the box to satisfy the additional power requirement.

 The upside of this arrangement being that I could wire it direct to the C6 mains inlet socket, bypassing the rear panel on/off switch meaning that whilst it remained plugged into an outlet, I could switch the generator off, leaving the OCXO undisturbed, ready for immediate use the next time it was switched back on - no warm delay and only some 200ppt of warm up drift over the next hour or so's run time rather than the several minutes it would otherwise require to get within a few ppb of frequency.

 Warmed up to operating temperature inside of some foam rubber insulation, these OCXOs only draw some 800mW or so of power which equates to some 1.3 watts at the mains socket after taking into account the losses in the 12v smpsu board. Relying on using the front panel on/off standby button only saves around 2 watts at most, reducing the consumption from around the 7 or 8 watt mark to around the 5 or 6 watt mark so the split mains supplies provided a handy energy saving feature without unduly stressing the OCXO with thermal retrace issues to compromise its accuracy and ageing drift rate.

 BTW, that requirement for supplying precisely 3.300 volts to those 20MHz OCXO modules may not be quite so critical as the datasheet states. The at temperature current demand is likely to be in the ballpark of 300mA at the specified 3.3v peaking at some 1150mA during the warmup phase.

 I suspect that as long as the supply voltage can be held above the three volt mark until the heater current drops down to half an amp, allowing the supply to come back onto its 3.3 volt setting, the worst you're likely to experience is a slightly longer warm up time. That maximum power consumption figure of 3.8 watts is remarkably similar to the 3.36W of those CQE 10MHz OCXOs of mine which on test were still able to reach operating temperature with a 5.2 volt supply and reach their intended frequency despite the sine output voltage being a little on the low side.

 The main symptom had simply been an even longer delay before the oscillator started showing signs of activity compared to the 10 to 15 seconds delay with the 13MHz unit when powered from the same 5.2v supply before eventually getting to temperature after some 8 minutes or so versus the more typical 3 minutes warmup of the 10MHz units when powered off a 12 v rail. Indeed, the 12v wasn't critical, I sometimes ran my breadboard builds off a 9v wallwart feeding the OCXO directly whilst feeding the 5 and 3.3v LDOs on the plug in breadboard's psu board, the only effect of this reduced voltage being an additional minute or so of warmup time.

 Of course, with 3.3v OCXOs, the exact voltage level does tend to be rather more critical than for a 5 volt version which, in its turn is a little more critical than the 12v versions. but as long as the voltage can recover to its stated requirement of 3.3v at a heater current level say some 50% greater than its final at temperature current demand, apart from a protracted warm up delay, it's likely to be just fine once it has warmed up.

 The main concern with these low voltage high current OCXOs being the greater risk of an LDO overheating and failing catastrophically even when fed off a 5v rail, with the risk of overvolting your precious OCXO with a fatal voltage surge. You might want to create a crowbar protection module using an LT431 set to trigger an SCR or triac at the 3.4v threshold to place in parallel with the OCXO (a fuse is optional - personally speaking, I'd rather blow the offending LDO to smithereens for its treachery than offer it any token gesture of protection with a fuse (Transistor :- a ten dollar device designed to protect a ten cent fuse)  :-DD ).

 Well, I think that's covered the points you raised and I hope my observations have been of some use.

JBG
« Last Edit: May 26, 2020, 12:47:53 am by Johnny B Good »
 

Offline Labrat101

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Thanks for that reply .
I found another problem .. but I'm sure some else may have noticed . I was running some voltage
drop tests was loosing 0.5 volt . I was still using the original ribbon cable with the plug to the
Board .. when examined it . each wire was made up of 5 strands of very thin wire only 3 of the five were actually connecting . So dismantled the plug and re soldered 6 new wires . into the crimps.
OK that was boring . but solved my power lose . also made some mods to my linear power supply
my 7805 were making my bridge rectifier hot.  I am using 16-0-16 & 12 volts this is what I had.
16-0-16 is for the -12 + 12  & the 12v winding for the 5v . so 12v going though the bridge + cap
was 16v and was a little high for the 7805 so I added a LM317 before to drop 16v to 9v better
arrangement for 7805s.
 The FY6800 draws 450ma  . and on standby 350ma . (real energy saver) :phew:.
So using the front button on standby saves a whopping 100ma . So 350ma is still used  :-DMM
Don't ask no I never measured the power usage before.  Sorry I did as well.
I was hoping to add another power out from the large transformer for my Ocxo  when it turns up.
 I had ponder about using a buck from the 16v to 4v LM317 to the final 3.3v. and use the LM317
as a safety device .  :blah:
I wont be adding the GPS part for me I don't require. I am aiming for just Zero Jitter   :-DD

 BTW Johnny can you give me some of your schematics and a few photos  :popcorn:
 



« Last Edit: May 25, 2020, 06:36:05 pm by Labrat101 »
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Offline Johnny B Good

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 It looks like you've discovered the very bad consequence of FeelElec's knee-jerk response to the "Feedback" they got in spades from the FY6600 topic thread over the half mains voltage ESD hazard to the more delicate DUT items when they redesigned the FY6800 to be blessed with a C14 3 pole mains receptacle to earth the ground rail to eliminate this ESD risk.

 They committed two cardinal sins. Firstly, they stole one of those six wires in that PSU to main board ribbon cable (one of only two ground return wires) as a very quick and shabby fix to connect the ground return directly to the PE tag of the C14 socket, thus compromising the ground rail noise rejection performance, and secondly, they introduced an earth loop problem that just simply hadn't existed in the FY6600 model by making a low impedance connection between the BNC grounds and the rather noisy mains earth with its random DC voltage offsets from galvanic and thermocouple effects in the mains earth wiring. Further, the stolen low voltage, low current rated single insulation wire passed very close to the mains live connection on the psu board, creating a potential fire and electrocution risk.

 All that was required to fix the original ESD risk in the FY6600 and its predecessor was an upgrade from the 2 pole C8 socket to a 3 pole C6 or C14 socket to provide access to the safety earth to allow a 4K7R to be installed between the PE tag and a handy ground return reference on the main board or the PSU board to short out the 1.5M ohm impedance circuit created by the 1nF Y cap down to ground potential attenuating the 90 odd volts in the case of 220 and 240 volt mains supplies down to a mere 250mV ac, whilst attenuating the unwanted earth loop interference effect by some 50 to 60 dB. They are still using a class II smpsu which simply doesn't require any such hard connected safety earth connection.

 Luckily for you, and every other proud owner of an FY680 or FY6900 function generator, all the hard work of the mod required by FY6600 owners has been done for you (the welcome presence of a C14 socket in place of the C8 used in the FY6600 and earlier models. The gross wiring errors (you've already dealt with one of them) are trivial to put right.

 Make good the damage to that ribbon cable connection and insert a 4K7 resistor between the PE tag and any convenient ground return connection on either the main board or the smpsu board (after undoing FeelElec's original "earth wire connection" bodge job) which takes you from a "Worst of both worlds" to a "Best of both worlds" situation.

 Quite honestly, it looks to me like FeelElec's response to their FY6600 owners' requests to fix the half live mains voltage ESD hazard was made out of pure spite rather than as a properly considered solution. Quite frankly, what they did, as with that cockamamie 85 ohm 20dB attenuator network, was an insult to the intelligence of all their customers.

 It seems to me that what FeelElec need is a Bean Counter in chief with a more balanced view of their primary function rather than the insane idiot that's currently in charge of the whole operation. Either that or employ a marketing guru who can veto such insane cost cutting decisions. That's my tuppence worth on FeelElec's recent bodgery activities for what it's worth (tuppence seems about right for all its effect on FeelElec's recent downward spiral into mediocrity).

 Regarding the assembling of an 'analogue' PSU replacement, the use of R-core transformers has been recommended as high efficiency candidates. I'm eyeing up this 30VA 115/230vac primary with 2x18v 0.6A and 2x9v .45A secondaries example here:

 https://www.ebay.co.uk/itm/115V-230V-30W-R-Core-Transformer-F-Audio-Amplifier-DAC-Output-9V-12V-15V-18V-24V/293120578266?hash=item443f5912da:m:mnHeM7YF_xVLtflXRAfuUfQ

 For a hybrid analogue transformer with switching buck regulators to provide the 5 volt and +/- 13v rails with minimal waste heat and minimal switching noise and ripple using the mini360 1.3A rated 24vdc max input to variable output voltage (5 and 13v settings) 7805 sized positive output buck regulators, utilising isolated rectified and smoothed 22v max from the 18v secondaries to allow one of the 13v positive buck converters to be connected 'backwards' onto the common ground rail (positive output connected to ground with its 0v 'ground' pin supplying the -13v rail. This would also be suitable for an analogue regulator based version provided you provide sufficient heatsinking and air cooling for those energy wasting 7805, 7812 and 7912 (or another 7812 wired 'backwards' as per my idea of using a positive buck converter fed from an isolated DC source).

 As I've implied, I'm hanging fire on actually ordering one of these 30VA R-core transformers since I've yet to test with battery power to confirm whether replacing the original smpsu board will offer any real improvement over the issue of power supply noise and ripple. It probably will but I don't want to just ASS-U-ME this is actually true since I don't want to make an ASS out of U and ME (well, ME, mostly).

 Since there'll plenty of waste heat being dished out by the analogue regulators, the last thing you want is a low efficiency transformer in that mix adding to your heat stress woes, hence the advice to choose a suitable R-Core transformer (and a 30VA rating seems the optimum choice in this case).

 I've never, afaicr, measured the actual current draw off the smpsu board's voltage rails (however, I can use my planned battery power test as an opportunity to examine this in detail). I've known about this rather poor energy saving of the front panel standby button almost from day one through my power consumption monitoring with that rarest of Unicorn droppings test kit, aka, an analogue watt meter showing the consumption from the wall outlet. If I want to be able to keep the OCXO continuously powered whilst the function generator is switched off if I do 'upgrade' the existing smpsu board with an R-Core transformer based alternative, I'll probably have to do away with that half amp 12v smpsu board to maximise the reduction in noise and ripple effects that could leak into the main circuit via the OCXO board's connection.

 Those 30VA R-Core transformers are fairly compact but I doubt I'd be able to squeeze a smaller 10VA version into the box with all of the current add-ons I've already stuffed it with (at least not without a radical rearrangement of its current contents). If I do go for the PSU upgrade, I'll probably have to re-shuffle things just to squeeze the 30VA transformer into the box anyway. At least with dc-dc buck converters, I don't have to also find accommodation for some ghastly heatsinks as well. Emulating my current power saving scheme is probably going to involve some switching control circuitry on the low voltage secondary side of the transformer with that rear panel mains switch used to control a low voltage signal instead of switching the mains voltage on and off. That R-core transformer will have an unswitched connection to the C6 mains socket just like the dedicated OCXO smpsu board is connected.

 The idea of building an all analogue psu doesn't appeal to me. I make enough "Rods for my back" as it is and this, with all the issues of the additional waste heat, this just seems like one rod too many for my liking, hence the hybrid of analogue transformer with rectifiers and smoothing caps feeding dc-dc buck converters instead of a bunch of analogue regulators on heatsinks.

 Incidentally, feeding an analogue regulator from a higher voltage one is a fairly standard trick to keep the dissipation down on the lower voltage one when fed from a higher than ideal rectified and smoothed supply voltage, usually done when there is a need for the higher voltage anyway such as 12v to feed a low current device which can be used to feed a 5v regulator that would otherwise have to handle the much higher voltage coming directly from the higher voltage raw rectified and smoothed supply optimised for the 12v regulator. It doesn't alter the overall energy consumption (and waste heat), it just helps balance the heat loading on each of the regulator ICs.

 In the case of those buck converters, optimising the raw rectified and smoothed voltage source doesn't matter so much, just as long as it stays below the maximum input voltage rating at all times (and typically, stays 2 volt above the set output voltage). Assuming those 18 and 9 volt secondaries are exactly matched by their turns ratio, I should be able to put the 9v windings in series and parallel the resulting 18v secondary with either or both of the 18v secondaries.

 That choice of secondary voltages does give me some flexibility in how I use them. I could use one of the 18v 0,6A secondaries to power my 'backwards' negative buck converter and create a 1.05A rated 18v secondary from the remaining 18v paralleled with the two 9v in series windings to power both the +13 and the +5 v buck regulators which can share a common zero rail connection. This will give me a beefed up 18v supply to handle the additional loading of a separate 12v buck converter (also sharing the same common ground return) for the OCXO supply.

 With dc-dc converters, there's nothing to be gained by cascading a lower output voltage converter from a higher voltage buck converter as there is with analogue regulators. The exception to this being a means by which to safely supply a 24v max input converter from a raw 35v supply which happens to be feeding a 40v max input rated converter providing a voltage that's below the 24v limit but at least 2 volts higher than the required output of the lower voltage rated converter.

 Most FY6600 modders started by replacing the original smpsu board but I've left this one till last simply because there seemed little point in making such an investment until most of the other improvements had been applied and proved worthwhile. I've always considered such a radical modification as being 'a nice final touch', hence it's being put on the back burner (along with that all too critical battery test required to validate the potential benefit of such a PSU upgrade).

 The main problem with such analogue psu designs (and the main reason why their efficiencies are little better than 50%) is that you have to account for the worst case scenario at maximum current demand which means allowing for the voltage regulation of the transformer and the variations in the mains supply voltage (-10 to +6 percent since the UK and European supply voltages became 'harmonised') as well as making additional allowances for the effects of capacitor ageing on the level of ripple voltage which eats into the drop out margins of the analogue regulators ( and, to a lesser extent, buck converter modules but only because more generous voltage margins can be applied without the heat penalty that applies in the case of analogue regulators). As I said, designing an analogue PSU is rather like making a rod for your own back.  :(

 Incidentally, when it comes to making up a 5v supply based on the classic 7805 or higher power equivalent, the general wisdom is to specify an 8vac secondary voltage. No wonder you were having overheating problems with your 7805 off that 12vac secondary. You wouldn't have had any problem using one of those buck regulators for the 5v rail which only supplies the digital components of the main board which would regard the switching ripple as 'Light relief' compared to all the noise generated from the switching operations of the logic chips themselves.

 If you do decide to use a dc-dc buck converter instead, the trick to avoiding pollution of the other power rails is to use a separate ground return connection to the mainboard's ground return rail from your 5v buck converter to prevent crosstalk via a ground return shared with the analogue supply rails. If possible, try to avoid running these analogue and digital supply ground returns in parallel as much as you possibly can to minimise any electromagnetic coupling between them (assuming the use of separate secondaries and rectifier/smoothing packs for the digital and analogue transformer supplies). If you have no choice but to use a common grounding point at the transformer end, the best you can do is use as short and as heavy a gauge of wire for the ground return link between the main board and the PSU to minimise resistive and reactive volt drop cross-coupling effects between the supply rails. It's all too easy to undo all your efforts at creating a low noise PSU with careless wiring layout.

 Regarding the use of a buck converter to drive an LM117-33, you can buy such readymade concoctions from the likes of Banggood for less than the cost of the separate components. I bought myself a couple of the 40 volt max input to 5v output versions (there's also a 3.3v version) to (eventually) try out one of these days. I'm not entirely convinced that the mere addition of an LDO to a buck converter in this way is as effective as most people seem to think, hence my sampling a couple to try for myself (when I have the time and the inclination to do so).

 The use of an external reference such as a GPSDO is probably overkill for most usage cases for these 'toy' function generators but it rather depends on what you're using it for. Even an OCXO upgrade would seem to be a matter of overkill by most owners of FeelElec's finest but, again. it depends on what you plan to use it for.

 In my case, I'm using it as a sanity check on my homebrewed GPSDO's performance. The frequency stability is so good now with the OCXO that it readily reveals just how good or badly my GPSDO is performing, revealing the limitation of the GPS system itself in its effect on a basic GPSDO that isn't blessed with a microcontroller to effectively smooth out the hour to hour phase shifts with a Kalman filtering algorithm and gather OCXO ageing frequency drift data to both assist the smoothing out process and provide an effective hold-over function to paper over any outages of service that might arise for any number of reasons. IOW, my GPSDO is so basic, it reveals all the shortcomings of a single frequency GNSS, "Warts and all". You'll be surprised at just what you can cut, given a sharp enough tool.  :)

 The OCXO upgrade will improve frequency stability and accuracy but I don't think it will add much improvement jitterwise with regard to the almost jitter free sine based waveforms. There seems to be around 300ps of random jitter on the Sinc pulse waveform which may, or may not, be better than it had been with the original XO (I never thought to check this until recently so couldn't offer a valid observation in this matter). This is vastly better than the systemic 4ns of jitter typically seen with square and rectangular waveforms (amongst others with an intrinsically high speed transient). TBH, I'm surprised that this random jitter is as low as it is, all things about this function generator considered. You might want to get some screen captures of the jitter effect on the Sinc pulse waveform before doing your OCXO upgrade to gather some "Before" (the upgrade) to go with your "After" (the upgrade) results.

 It's useful to have a target to aim for but I don't think you'll ever hit your "Zero jitter" target in this lifetime (even if you spent thousands on a high spec unit)  >:D

 As for your request for more pictures and diagrams, I don't have an organised collection I can dip into. It's mostly stuff that I'd downloaded from Der kammi's github repository and hand drawn circuit sketches on various scraps of paper. The only other (hand drawn) diagram I have to hand that's respectable enough to photograph and post to an EEVBlog topic thread is the one I drew up for my DIY GPSDO which I don't think is appropriate to this thread. I do plan on posting a picture of that diagram but to a GPSDO related thread, either my existing u-blox gps module thread or else a freshly started diy gpsdo topic thread, I haven't decided which.

 Most of what you're after can (eventually) be found in the original FY6600 topic thread if you search long enough. Sorry but that's the best I can offer.

 Meanwhile, in breaking news, I did manage to fix the "Theremin fault" that had afflicted my 3.000V dc offset reference for the EFC voltage monitoring meter connection. I was going to add a couple more of those 10uF ceramic caps between the Ref input terminal and the anode and cathode of the TL431 but only had space to fit the one between the anode and the ref terminals but this proved more than sufficient to immunise it against the RFI flying around inside the box (quite possibly from the adjacent buck regulator module's inductor).

 The voltage has been stable throughout all of yesterday (at least to within half a millivolt of its initial setting) so does seem to be operating over the flattest part of its tempco curve as the datasheets had implied would be the case. The residual theremin effect on the actual EFC voltage (the buffered version used to drive the meter test point) seems to be no more than half a tenth of a millivolt which may require nothing more than the addition of a 330 ohm 'stopper resistor in series with the feed going to the meter test socket at the junction with the 10uF ceramic cap and the 100 ohm 'stopper' resistor connected to the buffer amp's output.

 I'm not quite certain that this is actually another 'theremin' effect so it might make no difference whatsoever. I can only try it out and see if it works in eliminating the slight but observable shift in voltage that I'd witnessed.

 Also, I should mention that I've edited reply #14 to correct what I'd said in regard of that cheap Chinese 9999 counts DMM that I've been using to monitor the EFC voltage with. I think you may be interest in what I had to say about this DMM.  :)

JBG
« Last Edit: May 26, 2020, 08:13:38 am by Johnny B Good »
 
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Offline Labrat101

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My original power supply that came with my FY6800 lasted a whole hour and then gave off the
Magic Smoke and self destructed   :wtf:   that was last year .
So cutting a long story short .
I built a new linear power supply from parts salvage from the dumpster  ^-^
But I used the original ribbon cable with there plug . STUPID ..
..
My CTS OCXO 20Mhz 0.02 PPb turned up today .. So I just had to try it . the photo are below.
Look Dad its a Square wave .. . Rock solid .. on both of my scopes .
..
I also Re checked my replacement Gold Chinese TCXO 50Mhz that was supposed to be less than 0.01ppm
  Well its now got the Jelly wobbles .. "I am surprised Because!!"
I think that the cheesiness think that ppm means " Pretty Poorly Made "   :-DD
...
My supplier said he should have my 3N502 in at the begin of next month.
..
I took my transformer out of an old duel tape cassette player dumped . 16-0-16  + 12v nice haa. :-+
That transformer looks horrible .on that ebay link. half the winding are outside the loop . If that was me I would leave it .
It looks like an the old line transformer we had on a 500w tube PA 45 years ago. it gets HOT but it was not noticed as the tubes were Hotter. it was used to feed 100v to the speakers .The coils work loose and buss.
Another cheesiness dig up . There is a few youtube videos  Sorry I was not impressed ..
you would be better to look for a toroidal transformer..  Use to be able to get the 12v lighting ones.
12v ac by the time its rectified & caped it will be 16v . and the small ones are about 50w or 100w and they are made in the UK.
Remember  require 450ma . on the 5v side.  so you require x 2 at least and then it will power you Ocxo as well . all in 1 box.
I guess yours is about the same .
The 12-0-12 only powers the out put op amps so that is small .plus any load you have connected I think the Max 250ma if you changed the 2 out put op's.
...
Also you mentioned you want your ocxo to run all the time .. Why? . The ones I got were fully stable after
2 mins. Mind you it is a bit warmer here than the UK. 
The jitter is easy to measure on my HP as it has a Glitch mode . and it shows 4ns very nicely .
This one thing that is missing on my Digital. . But the HP Agilent has the TV /Frame/ Glitch/  addon board.
Maybe 25 years old but its still reads true . and way faster response time.
Also have an even older Tektronix Steam powered under the desk.
Just save to memory the jitter but that would mean pushing a button ..

 I now found another problem were the old xtal sits there is a track that goes past another chip
and then to a 330 ohm smd resistor then to pin 24 of the cyclone iv the track just broke off on its own and my signal went . With my ninja soldering iron repaired it . when I put the piggy back in
with the PPL I will redo all of that section .
I have this feeling by the time I get it work perfectly the board will fail ..  :palm:
An the thought of doing all this over again .  :scared:

BTW I think I have found you the ideal Transformer ..    (bottom photo)  >:D

RNS.
« Last Edit: May 26, 2020, 10:08:53 pm by Labrat101 »
If it's Gets Hot its Working. If its Getting cold! it's your Coffee.
 

Offline Johnny B Good

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My original power supply that came with my FY6800 lasted a whole hour and then gave off the
Magic Smoke and self destructed   :wtf:   that was last year .

 That was damned unlucky :( Mine has not only survived a year and a half but it has done so with plenty of modding abuse from yours truly (including adding, then removing, an extra two turns on each of the 12v windings ::) )

So cutting a long story short .
I built a new linear power supply from parts salvage from the dumpster  ^-^
But I used the original ribbon cable with there plug . STUPID ..
..
My CTS OCXO 20Mhz 0.02 PPb turned up today .. So I just had to try it . the photo are below.
Look Dad its a Square wave .. . Rock solid .. on both of my scopes .

 That looks dead on a perfect 1:1 ratio square wave. The typical spec for OCXO square wave outputs is a 45 to 55 % mark/space ratio.
..

I also Re checked my replacement Gold Chinese TCXO 50Mhz that was supposed to be less than 0.01ppm
  Well its now got the Jelly wobbles .. "I am surprised Because!!"
I think that the cheesiness think that ppm means " Pretty Poorly Made "   :-DD
...

 The usual spec for TCXOs is 0.1ppm (100ppb). If they actually claimed 0.01ppm (10ppb) then it was either a fabrication or a typo on the seller's part. The best you can wring out of these TCXOs is some +/- 30 to 50ppb as I discovered about a year back with my first XO upgrade.

My supplier said he should have my 3N502 in at the begin of next month.
..
I took my transformer out of an old duel tape cassette player dumped . 16-0-16  + 12v nice haa. :-+

 That explains all the Mu-metal shielding then. Those 3n502 clock multiplier ICs aren't cheap, are they? :(

That transformer looks horrible .on that ebay link. half the winding are outside the loop . If that was me I would leave it .
It looks like an the old line transformer we had on a 500w tube PA 45 years ago. it gets HOT but it was not noticed as the tubes were Hotter. it was used to feed 100v to the speakers .The coils work loose and buss.
Another cheesiness dig up . There is a few youtube videos  Sorry I was not impressed ..
you would be better to look for a toroidal transformer..  Use to be able to get the 12v lighting ones.
12v ac by the time its rectified & caped it will be 16v . and the small ones are about 50w or 100w and they are made in the UK.
Remember  require 450ma . on the 5v side.  so you require x 2 at least and then it will power you Ocxo as well . all in 1 box.
I guess yours is about the same .

Perhaps a little higher on account of the fan and a few extra milliamps for the injection locking module (it rather depends on where you're powering that fan in yours from).

 I'm not quite sure what you find so horrible about that transformer. It looks no different to every other 30VA R-core transformer I've seen pictured on Ebay. The R-core transformer is a close cousin to the toroidal kind, sharing the same low external flux leakage characteristic. The main difference is the sacrificing of some of the tight coupling between the windings of the toroidal design to reduce manufacturing costs.

  The bobbins are a split type designed to be clipped over the limbs of the core and taped, allowing the coil winding machinery to spin the bobbin on the limb of the core to effect loading of the turns of wire without any need for a complicated shuttle winding mechanism that requires a complex handling sequence by human labour to thread the wire onto a toroidal core.

 The more compact version of these 30VA transformers look like they may fit into the space vacated by the original smpsu board. If this proves to be the case, that will neatly avoid the need for a radical repacking of my add-ons. I can tuck the rectifiers and smoothing caps into almost any available free space as I can do with the buck converter modules which don't require being mounted onto bulky heatsinks (just kept apart and in the cooling flow of air from the fan to prevent being 'slow cooked' by their own modest level of waste heat in a location poorly served by said cooling fan).

 Going by the 10W maximum draw when outputting 20MHz square waves into 50 ohm loads (about 3.5W average drawn off the 12v rails from a PSU I've reasonably assumed  to be around 80% efficient), I'm guessing the other 4.5W was being drawn off the 5v rail (around 900mA or so). I'd be inclined to assume a worst case loading requirement of 1100mA to future proof it against any additional add-ons and also assume the worst case of double the loading on either one or the other 12v rail at any one time in the event of outputting a plus or minus 10v DC on both channels simultaneously into 50 ohm dummy loads, representing the possibility of a sustained 550mA draw from either one or the other 12v rail at any one time, worst case (for the individual 12v buck converter being so abused in this rather extreme scenario).
_______________________________________________________________________________________________
[EDIT 2020-05-28]

 Oops! I did it again :palm: I forgot (Yet Again!) that the 20V pk-pk setting gives a 10V peak open circuit which is halved when driving a 50 ohm load down to a 5V maximum plus or minus voltage (whether DC or the peak amplitudes of a bi-polar square wave).

 In this case, I was trying to estimate the wattage used by the 5v logic from my worst case 20V pk-pk setting with a square waveform into 50 ohm loads on both channels. The peak current (5V/50 ohms) works out to be 100mA for each channel (200mA total) for 50% of the time on each of the 12v rails, Add in the 17mA vampire loading of each THS3491 opamp, then the 25mA for each of the opamps driving the 3491s plus another 16mA or so on top to account for their vampire loadings and we arrive at an average of 100+25+17 +16 mA per 12v rail (158mA). Round up to 160mA and double up to 320mA from the 12.7v rails to calculate a total of 4.064W and round it down to 4W to subtract this power from my 8W estimate that isn't accounted for by the 5volt rail to get another 4W @5v which works out to an 800mA demand upon the 5v rail.

 The aim of these calculations is to inform you of the worst case maximum sustained loadings you can expect your voltage regulators or buck converters to handle (the same polarity DC output at max voltage into 50 ohm loads from both channels simultaneously or ditto for square waves at very low frequencies (say 100mHz or lower).

 The total power from both 12v rails remains the same regardless as far as calculating a minimum VA rating for the mains transformer is concerned. Calculating this requirement for a buck converter based solution is much simpler than for the analogue voltage regulator case since the 5 to 15% lossess remain almost constant over the full allowable voltage difference range between rectified smoothed output feeding each buck converter and its set output voltage.

 For example, the buck converters I plan on using will be the same 1.3A max (1A continuous) Mini 360 module I'm using in my GPSDO for its 5v rail. Testing over an input voltage ranging from 7 to 24 showed a consumption that stayed within 50mW of the 1.8W it consumes after the OCXO has reached operating temperature. A pessimistic estimate of just 90% efficiency for these synchronous rectified buck converters will get me very close to the total loading on the transformer's secondary winding outputs. Of course, the additional capacitor smoothing ripple current will increase the I squared R losses in the windings but a reasonable 'de-rating' estimate can be made to allow for this effect by assuming a peak current of twice the average for 50% of the time to get a RMS figure.

 I reckon as a reasonable rule of thumb, that using a transformer with a VA rating double that of the original worst case demand (10W in this case) for a buck converter based replacement PSU  (I'm planning on using a 25 or 30VA transformer to account for the OCXO's demands) and triple that for an analogue regulator based one, are just about the optimum choice of transformer rating. If space permits, err on the larger size rather than the smaller since this will reduce I squared R losses due to smoothing cap ripple current.

[/END EDIT]
---------------------------------------------------------------------------------------------------------------------------------------------------------------

 I was about to mention the additional loading on the +13v rail to power the OCXO during its warmup phase but I'm planning on using a separate buck converter (fed by the same +18v rectified secondary winding) for this task simply to provide the OCXO with its specified 12 volts whilst providing the extra volt of headroom on the THS3495s' (or the original  THS 3002i dual opamp's) supply rails to avoid the risk of clipping with a modest +/-1v DC offset applied.

 Powering the OCXO's buck converter from the same rectified and smoothed secondary as the +13v buck converter feeding the opamps' positive supply rail might seem like a bad idea but the full heater current loading will, at worst, be a short term 3 minutes or so affair that the transformer is more than capable of handling. The much lower 'at temperature' demand is unlikely to represent much above an extra watt's worth of loading alongside of the worst case demand by the opamps on the positive rail being presented by the buck converter as a maximum in the region of 5 watts, comfortably within the 10.8VA rating of that 18v 0.6A secondary which, in this extreme scenario, won't be having to cope with the heating effect from the other 18v winding used to power the negative buck converter.

 In the interests of minimising pollution of the analogue supplies' ground return from the 5v logic supply's ground return current via a common ground return rail, I've decided to reserve the two 9v windings for a bi-phase rectified supply to the 5v buck converter - hence the use of one of the 18v windings as a common power feed for the OCXO and the positive 13 volt opamp supply rail. Using a single mains transformer to power everything means that I'll have to incorporate switching circuitry to allow the OCXO to remain powered up whilst the rest of the function generator's DC rails are disabled if I wish to keep the same standby power saving scheme as my current setup.


The 12-0-12 only powers the out put op amps so that is small .plus any load you have connected I think the Max 250ma if you changed the 2 out put op's.

 Unless you want to completely forego the option of using "DC waveforms driving into 50 ohm loads", I'd say your estimate of the opamp supply rail's requirements are a little on the low side. You need to figure out the actual absolute worst case scenario, power demandwise, on the +/-12v rails lest you be caught short later on when trying to utilise the DC waveform options. You need to make conservative estimates of your power requirements when attempting to size up the power supply unit. It's far better to overestimate by 30% than to underestimate by 3% when calculating these requirements.

 The individual analogue regulators might be ok when the loading is being shared equally between them in the case of actual waveforms but when using the "DC Waveform" (or a square wave at an extremely low frequency - say 100mHz or lower) where the total demand is concentrated on one or the other for any length of time, this might be the 'Last Straw' for the regulator in question, especially when they're mounted on individual heatsinks. This is why it's a good idea to mount the 12v regulators onto a single large heatsink to mitigate any such potential overloading effects.

...
Also you mentioned you want your ocxo to run all the time .. Why? . The ones I got were fully stable after
2 mins. Mind you it is a bit warmer here than the UK.

 The warmup delay, whilst something of a minor irritation in this case isn't really the issue (it's normal practice to power up function generators and the like as soon as you start your "day in the lab", well in advance of the time you'll be running your first test and measurement sessions). The problem, quite apart from the extra stresses imposed by such daily thermal cycling on the equipment concerned, is this business of retrace and ageing of OCXOs subjected to such power cycling abuse.

 You need to keep in mind that the target temperature for the C cut crystal resonators used in OCXOs is anywhere from 65 to 85 deg C which is quite a wide temperature excursion from room temperature that, given enough such cycling, can result in thermal stress induced fatigue failures.

 That and, mostly, the resulting erratic ageing effect and retrace issues from such maltreatment is why those who take accuracy seriously, avoid needlessly power cycling their OCXOs. A quality OCXO is rather like a fine wine in that, given a stable environment, it will age gracefully to eventually remain within a few dozen ppt, or better, of their calibrated frequency after a good six months to a year. Like a properly stored fine wine, they generally just get better with age.

 Since, like many fine wines, they also represent an expensive investment in both time and money, taking such a cavalier attitude in their treatment tends to be regarded as a cardinal sin by anyone with the slightest interest in the fine art of metrology. Daily power cycling, let alone hourly power cycling in some cases, is something to be avoided if at all possible, especially if you wish to get the best out of your investment.

 
The jitter is easy to measure on my HP as it has a Glitch mode . and it shows 4ns very nicely .
This one thing that is missing on my Digital. . But the HP Agilent has the TV /Frame/ Glitch/  addon board.
Maybe 25 years old but its still reads true . and way faster response time.
Also have an even older Tektronix Steam powered under the desk.
Just save to memory the jitter but that would mean pushing a button ..

 The main difference between venerable high quality T&M kit from decades ago and today's modern T&M kit that equals or exceeds the performance of such kit for a fraction of its original cost in dollar terms even before the correction for inflation has been applied is essentially and quite literally its 'gravitas'  ::) A quick 'n' dirty way to estimate the original price of a twenty year old equivalent of a modern day DSO is to compare their weight and multiply the price of the current  item by their mass ratio. I reckon you wouldn't be too far of the mark with this method of assessing the price of high spec vintage kit.  :)


I now found another problem were the old xtal sits there is a track that goes past another chip
and then to a 330 ohm smd resistor then to pin 24 of the cyclone iv the track just broke off on its own and my signal went

 I suspect that that "330" ohm resistor is, in fact, a 33 ohm resistor (I do remember there being one right at the XO's output pin on the FY6600's mainboard). If it was marked with the digits "330", that's the equivalent of an orange, orange, black colour coded wire ended resistor expressed by the numerical equivalents of that colour coding scheme where the third band or digit represents the power of ten multiplier for the 1st two digits (33 times ten to the power of zero, aka 33 ohms - any number to the power of zero being "1").

 33 ohm resistors are a commonly used series damping resistor value at the driven end of high speed circuit traces. If that resistor was marked "331", then I've been completely off the mark and it is a 330 ohm resistor after all, in which case I haven't. offhand, got any clue as to its function in the circuit. ::)

. With my ninja soldering iron repaired it . when I put the piggy back in
with the PPL I will redo all of that section .
I have this feeling by the time I get it work perfectly the board will fail ..  :palm:
An the thought of doing all this over again .  :scared:

 That's normal. I've been living with that feeling for the past 18 months or so ever since I purchased mine. ;D

BTW I think I have found you the ideal Transformer ..    (bottom photo)  >:D

RNS.

 Yeah, well it would certainly lend considerable gravitas to our 700 gram weakling.  :-DD

JBG

P.S. I've attached a few photos for your viewing pleasure.  >:D

P.P.S. Those 10MHz spectra (SDS00232 and SDS00236) are my "Before" (the 10MHz XTAL upgrade to the GPSDO's LPF filter) shots. I'm planning to record repeat spectra to check the effect of the XTAL add-on which had significantly reduced the jitter on the 10MHz sine wave output from my DIY GPSDO. I'm anticipating a significant reduction in the level of those close in sideband artefacts lying just under +/- 1.5KHz away from the carrier.

[EDIT] I've pulled the 1.2MHz noise spike picture (it was the wrong image) and replaced it with the correct image, now last in the sequence of attached images.
« Last Edit: May 28, 2020, 03:48:59 pm by Johnny B Good »
 
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Offline Labrat101

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Yup.
I replaced that resistor yes i know it was a 33ohm . I just used a 1% 33ohm 1/8w cut one wire to about 1/4inch
bent it at right angles and soldered it onto the chip leg and the the remains of the track going to the were the old xtal was . and left the resistor vertical. going to my tcxo . temp job .. it works fine  ^-^
..
Also your board layout is a bit different to my one nothing major .
Did you noticed those empty pins on the cyclone they are all clock inputs to the internal PLL . I was reading
though some of the manual for this chip .. Then I suddenly realized its a Clone on your photo it shows the same number as far as i can make out .
There should be 4 banks of PLL with xtal switching incorporated I was hoping to see if I could use one of the
other inputs. the input that is used now is clk 1 n0 the  next one up is switchable with a 180 phase shift .
I am not sure you can see it on your scope . in glitch mode I can see the 4ns jitter is Negative so we need a
positive to cancel .  In the documents it says you can have 2 xtal inputs and the internal DAC will flick
between the inputs . they are mark n & p
This is a little out of my field of knowledge . 
 I might try it .. What can Happen ..  Rub lamp .. Get 3 wishes ... Poof ...
1. Magic Smoke ...
2. It will work ..
3. Does nothing. ..
...
My power rails are all showing no noise even on the scope lowest settings. I have Tantrum caps on the 78xxs
 ...
Your SMPS looks so clean after a year or so .. My one looked more crispy . Morning toast..
...
 Nice photos .  I am glade you liked my transformer recommendation ,I thought that might put a smile on your face ..  I was born in Kingston Apon Thames. there are a lot of good transformer manufacturers around
in the UK I would go for a toroidal . The R core that come from Japan are good . the one you are looking at
is from china there is a big difference  Q factor. and it was 18 quid .. buy local.
...
I am getting 4x  3n502 @ $5 each  I have notice that the price vary from country to country only the price symbol changes. and not getting clones . which are hard to spot by eye .
...
The OCXO i must admit I don't remember ever using one before . always used the regular xtals  & tcxo.
...
With regards to the Buck DC DC . I have the one which is CC CV . so it can have the amps set . works really well and also I measured the noise on the HP  dv/dt @ 20ns  got 10mv small peeks .
at that level it could even be my plug connection to scope.  on the Digital its a flat line .
I use one of these in my bench power supply as well 5A which also has a 12A dummy load my last project.
It mark as HW-083 5A CC CV DC DC converter Ebay. they are really good. and the Amp trip is fast.
...
You ask about the fan its a 6v running from the 5v line . I have no power noise. I used this as I opened the
side dummy vents so I get Laminar air flow across the whole broad surface. Nice @ Cool.
...
I think that I have wasted my time .. but I have a lot. .. If I had got the Siglent i would have got bored ..
But save money in the long run  :popcorn:  :-DD..
..
UPdate  Johnny look at the Siglent SDG2000x series they show the jitter @ 1.000001mhz 1 clock
and also there noise reduction is worse than mine after that small mod I did 10pf . I have no top or bottom
noise on the square wave it was caused by the relay contacts and the op amp . and up to 8.4ns .. on others.
so maybe we should patent some of our ideas .. :popcorn:  ;D  :-+

RNS


« Last Edit: May 27, 2020, 09:18:31 pm by Labrat101 »
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Offline Johnny B Good

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Yup.
I replaced that resistor yes i know it was a 33ohm . I just used a 1% 33ohm 1/8w cut one wire to about 1/4inch
bent it at right angles and soldered it onto the chip leg and the the remains of the track going to the were the old xtal was . and left the resistor vertical. going to my tcxo . temp job .. it works fine  ^-^
..
Also your board layout is a bit different to my one nothing major .
Did you noticed those empty pins on the cyclone they are all clock inputs to the internal PLL . I was reading
though some of the manual for this chip .. Then I suddenly realized its a Clone on your photo it shows the same number as far as i can make out .
There should be 4 banks of PLL with xtal switching incorporated I was hoping to see if I could use one of the
other inputs. the input that is used now is clk 1 n0 the  next one up is switchable with a 180 phase shift .
I am not sure you can see it on your scope . in glitch mode I can see the 4ns jitter is Negative so we need a
positive to cancel .  In the documents it says you can have 2 xtal inputs and the internal DAC will flick
between the inputs . they are mark n & p
This is a little out of my field of knowledge . 
 I might try it .. What can Happen ..  Rub lamp .. Get 3 wishes ... Poof ...
1. Magic Smoke ...
2. It will work ..
3. Does nothing. ..

 I'd been a little concerned that you might have misidentified that resistor. I was just a little bit puzzled that it had been placed so far from the XO's output pin when I looked at those photos since they're often used as a 'stopper resistor' to prevent unwanted feedback or instability issues (I found I needed to connect to those 3N502s's output pins with a 100 to 330 ohm resistor on my solderless breadboard layouts to stop them oscillating at hundreds of MHz).

 That Cyclone FPGA IC is a closed book as far as I'm concerned (I'd had a look at its data sheet and my eyes glazed over (MEGO) after just a few dozen pages of a hundred or more page document). That's way too much complexity packed into just one LSI chip for me to get my head around these days (or even back in the good old days of Z80 cpus and their support chips when I still had sufficient motivation to study their inner workings).

 Kit like that is normally programmed/configured using software tools (I don't have) to do all the donkeywork. I doubt even those who are programming them (FeelElec for one) fully understand their inner workings so I see little point in trying to nibble away at the edges of this technology at an amateur level whilst there are plenty of other aspects of the FY6600 that I do understand and can do something about.

...
My power rails are all showing no noise even on the scope lowest settings. I have Tantrum caps on the 78xxs

 Well, decoupling caps around these Old Skool voltage regulator ICs are an essential requirement (tants or ceramics) and, considering the heat penalty you're paying for the privilege of low noise, I should bloody well hope you're not seeing any noise on their outputs. ;)

...
Your SMPS looks so clean after a year or so .. My one looked more crispy . Morning toast..

 I'm surprised you think so after all the experimental mods I've subjected it to over its first 12 months of my stewardship. That last and final (I'm almost sure it's the final mod  ::)) with the single turn buck winding to effectively reduce the 5v secondary by one turn to efficiently boost the 12v rails without cooking the logic circuitry and the three LDOs close to the XO chip location was done some six months ago. I don't think there's much more I can do now to improve it. Any further improvements I'll be attempting will be along the lines of a replacement PSU.

...
 Nice photos .  I am glade you liked my transformer recommendation ,I thought that might put a smile on your face ..  I was born in Kingston Apon Thames. there are a lot of good transformer manufacturers around
in the UK I would go for a toroidal . The R core that come from Japan are good . the one you are looking at
is from china there is a big difference  Q factor. and it was 18 quid .. buy local.

 After reading your comments on R-Core and toroidal type transformers, I did an Ebay search to check pricing and availability of toroidal transformers. I found a UK supplier selling various 30VA for just £18.00 and free postage but, as with all the other toroidal transformers I'd checked out, none of them with more than two secondary windings on offer.

 Since I need three separate secondaries so I can use a positive buck regulator in reverse for the -13v rail and keep the 5v buck converter's ground rail separate from the analogue supplies' (the +/-13v and the OCXO's +12v) ground return, it seems I'm stuck with an R-Core transformer solution since these are commonly available with up to 4 separate secondary windings.

 However, I'm only weighing up my transformer options right now since I've yet to test with battery power to verify whether there's any point in replacing the original smpsu board with a quieter psu.

 BTW, I owe you an apology over the estimated psu requirements. It turns out your estimate of 250mA on the +/-12v rails wasn't quite as far out as I'd miscalculated (by overlooking the fact that the 20V pk-pk is the open circuit voltage with a peak amplitude of 10 volts in each direction which halves when driving a 50 ohm load :-[ :palm:).

 This is a peak current of 100mA per channel for 50% of the time with most alternating waveforms on each rail with a further 25mA of drive from the preceding opamps, plus 17mA vampire current from each THS3491 and, at a guess, another 8mA vampire loading for each of the two driving opamps and a further 25mA allowance for other odds and ends powered from the 12v rails, a grand total of 325mA or so peak on one or the other rail when using both channels to generate a DC voltage of 5 into 50 ohm dummy loads at the same polarity, leaving the other rail ticking over with just 75mA or so of vampire load.

 With a +/-13v supply, this represents a total worst case power demand between the two rails of 5.2W whether concentrated onto just one or the other rail or shared equally between them. I have since edited my previous post to correct my miscalculations. :-[

...
I am getting 4x  3n502 @ $5 each  I have notice that the price vary from country to country only the price symbol changes. and not getting clones . which are hard to spot by eye .
...
The OCXO i must admit I don't remember ever using one before . always used the regular xtals  & tcxo.

 That $5 price is less than the £5 or so I'd paid for each of a pack of three last year. That trick of just swapping the $ sign for the £ sign was typical of the Tandy Stores (aka Radioshack) pricing policy back in the day before their over-priced operation went deservedly bust some thirty years ago here in the UK. I still have my Zaks  "Programming the Z80" book with its $9.99 price sticker that I'd been charged £9.99 for by Tandy as a bitter reminder of that sharp practice.  >:(

 Until I tried the game of "Chasing Will of the Wisp" trying to match the FY6600's frequency against regular XOs both before and after upgrading to a 50MHz 0.1ppm TCXO module, I hadn't really appreciated the true worth of an OCXO for its supreme stability. The TCXO upgrade had made this game a little easier to win and the OCXO a little more easier again when the only player in the game remained the rather unstable XOs I'd been playing with (a bunch of metal canned DIP XOs).

 Testing against another of my stock of 10MHz OCXOs to determine the true cause of the jitter between my GPSDO and the FY6600 was a whole new ball game where my aim went from trying to stop the drift from degenerating into a jumbled mess on the DSO's screen to trying to keep it within one cycle of drift for more than ten or fifteen minutes at a time in order to examine the jitter with a 1ns per div timebase setting.

 The main issue with TCXOs, apart from the three orders of magnitude difference in stability, is that of the 'retrace' effect upon the temperature compensation circuit's ability to hold it on frequency. If there is a large temperature excursion from low to high and back to low, the TC circuit mitigates the detuning effect of the change in temperature but not perfectly and, what's worse, when it returns to its original temperature the crystal doesn't retrace this change exactly leaving it slightly off the frequency it had started from with the tuning compensation that the TC circuit had been using at the time which it would have restored since it can only respond to the temperature changes. A TCXO is an improvement over the ordinary XO but it's a very much imperfect solution.

 The OCXO gets round this retrace issue by not allowing the crystal to suffer any changes of temperature once it has warmed up and reached a stable temperature somewhere around the 65 to 85 deg C mark. I'm not sure just how tight a temperature control is applied, possibly as tight as +/-0.1 deg C or, since a C cut crystal has an inflection in its tempco curve at around the 65 to 85 degree mark, a slacker +/-0'5 degree may suffice at this temperature curve inflection point. Once an OCXO has had a few days to settle out any retrace effect from the last time it had been allowed to reach room temperature,what largely remains is ageing drift which, in a GPSDO or a Rubidium standard, is disciplined out or else manually re-calibrated against a standard reference on a routine basis.

 Since the crystal is isolated from the slightest of changes in temperature once fully warmed up, it never has to suffer retrace except for those occasions when it is powered down and back up again. That's why it's considered bad practice to subject them to regular power cycling events since it prevents them from attaining the supreme stability and accuracy they'd otherwise be able to achieve. Of course, even abused in this way, they're still an order or two of magnitude better
than the humble TCXO in stability and accuracy which might be all that is called for.

...
With regards to the Buck DC DC . I have the one which is CC CV . so it can have the amps set . works really well and also I measured the noise on the HP  dv/dt @ 20ns  got 10mv small peeks .
at that level it could even be my plug connection to scope.  on the Digital its a flat line .
I use one of these in my bench power supply as well 5A which also has a 12A dummy load my last project.
It mark as HW-083 5A CC CV DC DC converter Ebay. they are really good. and the Amp trip is fast.
...
You ask about the fan its a 6v running from the 5v line . I have no power noise. I used this as I opened the
side dummy vents so I get Laminar air flow across the whole broad surface. Nice @ Cool.

 That sounds like a reference to those buck converter kits for building a DIY bench supply using a suitable fixed voltage source (battery or 24 or 36 volt 5 or 10 amp smpsu) which include a display screen and voltage and current control knobs. I came across a bunch of them with various voltage and current capabilities on the Banggood website which looked a rather appealing way of building a modest DIY variable voltage bench supply, particularly if you happened to already possess a suitable fixed voltage smpsu and enclosure to build everything into.

 They were quite cheap for the 5A 15 volt units but, by the time you were looking to build a 32V 10A bench supply, the price wasn't far short of one of the Longwei 32v 10A ready made bench supplies before you'd even included the cost of a 36v 10A smpsu to power it from. I landed up buying a Longwei KW-K3010D bench supply with 4 digit voltage and current displays for just under 40 quid.

 Having seen a few youtube review videos, I knew I'd have to open it up to check (and remedy) the push-pull pair of HT switching transistors leaning towards each other and threatening to short out the hot ends of the switching transformer and go bang in a big way just as some other Banggood customer had described his letting out its magic smoke just an hour or so after he'd started using it (a review I didn't come across until a few months after I'd purchased mine).

 I'd taken the precaution of researching the product so as to be forewarned of such all too common examples of careless Chinese construction of their smpsu powered kit so had neatly neutered this particular time bomb before it had any chance to cause me any grief. Whilst I had the thing apart, I also disconnected the 120/240 volt selector switch wiring which links two points in the rectifier/smoothing circuit which converts it from a fullwave bridge with the two 200v rated smoothing caps in series into a fullwave voltage doubler for use with 120v mains since I had no immediate plans to move lock stock and barrel to a country where the domestic electricity supply is based on a 120v standard. Kit fitted with such mains voltage selector switches destined never to leave UK shores are simply a disaster waiting to happen.

 You might think the little smpsu board in the FeelTech/FeelElec function generators are low quality but compared to most Chinese smpsu product it's a model example of safety and (IME at least) reliability. Also, worthy of note, the design has inherent parity in the plus and minus 12 volt rail amperage ratings, perfectly matching a design requirement for powering opamps from bi-polar supply rails. You try and find any dual 12 or 15 volt rail smpsus that have such a feature (and in the unlikely event that you do succeed in this "Holy Grail" quest, please let me know).

 Every single one I've ever seen being offered on Ebay and Amazon and elsewhere have, without exception claimed a higher current rating for their positive 12 or 15 volt rail compared to that of the negative rail, typically in the ratio of 2 to 1 and 3 to 1 and often with the proviso that the positive rail have a minimum loading before the negative rail starts producing any voltage that comes within the claimed half a volt lower than the positive rail.

 That 6 volt fan mustn't be a whole lot quieter than normal with such a tiny reduction in voltage. I don't for one moment doubt it keeps everything nice and cool. ;) The little 40mm square fan I'm using is a 12 volt axial fan which I'm running very quietly off the 5 volt rail. Cutting a 38mm diameter hole in the base to accommodate it means I can use all of the existing vent slots as exhaust vents (including the rear panel vent slots covered with clear plastic ducting to force the air flow from the fan to go the scenic route before it eventually exhausts out of those rear panel (and side) slots.

 There's no nonsense with thermostatic fan speed control since even at reduced speed it upgrades the original, almost non existent, airflow to an actual flow of cooling air between the outside and the inside of the case, vastly reducing the otherwise excessive interior temperature it had suffered through reliance on only the barest hint of thermosyphonic effect which was completely nullified when propped up on its bail stand.

...
I think that I have wasted my time .. but I have a lot. .. If I had got the Siglent i would have got bored ..
But save money in the long run  :popcorn:  :-DD..
..
UPdate  Johnny look at the Siglent SDG2000x series they show the jitter @ 1.000001mhz 1 clock
and also there noise reduction is worse than mine after that small mod I did 10pf . I have no top or bottom
noise on the square wave it was caused by the relay contacts and the op amp . and up to 8.4ns .. on others.
so maybe we should patent some of our ideas .. :popcorn:  ;D  :-+

RNS

 I downloaded the datasheets for both the 1000 and 2000 series some time ago and, for the money, I wasn't particularly impressed. The reason why I chose to spend my money on the FY6600-60M was because the 5 to 7 fold price hike for a product that was in some respects inferior to the Feeltech had seemed rather too much for what Siglent were offering, especially as the 40MHz SDG1000 was only a fiver cheaper than their SDS1202X-E which had 5 times the bandwidth, rather more controls, and a much higher resolution display panel. I just couldn't see why generating a signal could be so much more expensive than examining it (especially in view of FeelTech's achievement). Maybe someone will explain it to me one of these days. :popcorn:

 Since this is a hobby activity for the pleasure of learning more about electronics and modifying a cheap bit of kit into something with better functionality than the bean counters had allowed along with other little side projects, rather than an attempt to meet a commercial deadline.

 That FY6600 has been a much wiser investment than an over-priced ready to go function generator from Siglent. Their SDS1202X-E DSO, otoh, has been an excellent and surprisingly cheap investment by comparison.

JBG
« Last Edit: May 29, 2020, 03:04:07 pm by Johnny B Good »
 

Offline Labrat101

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Hi Johnny .
A question was your OCXO a sine or a square wave outPut ?

Because my ocxo is a square wave can I feed it directly into the 3n502 or will I have to do what you did run it thought the 74hc14 . I don't have a 74hc14 but I have its equivalent cd40106 just the voltage the voltage range differs .  :-+
I am going to make your circuit any way as it looks good . and not to complicated .
Was that the final drawing you up loaded ?
you used 3x 150 ohm loading on your output to the 3n502 PLL  to give the Y connection 50 ohm  :-+
 the only difference is that my OCXO is 20Mhz so I will set the PLL to 2.5x instead of 5 .
every thing else should be good to go .. I have some 10MHz xtals so that part is the same .
the isolation cap that's a ceramic 1uf correct as the drawing was a bit smudgy in places
and 27pf .. not sure I have that odd value .
That choke you used 4.6uH  I can only find 4.7uH .. It will have to do I can't find a listing for 4.6uH or you made it??
But I am read to go for the build ..
Still waiting for my PLL chip will be another week so that will give me time to make Magic smoke.

Thanks RNS


« Last Edit: May 29, 2020, 08:07:19 pm by Labrat101 »
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Offline Johnny B Good

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Hi Johnny .
A question was your OCXO a sine or a square wave outPut ?

 The very first of these CQE OCXOs (which I'd blagged from a stall holder displaying this 'find' amongst a collection of 'tat' for just £4 at the Blackpool radioham mobile rally just over a year ago) was a 13MHz unit with a square wave output. It wasn't one of the 10MHz units I'd hoped to see on sale at this event but, in spite of this (and out of some frustration), I felt it would be worth taking a punt on it at the 4 quid price I'd managed to negotiate.

 Heck! At least it was an OCXO, even if was the 'wrong frequency' since, even if I couldn't use it to generate a 10MHz signal locked to a GPS, I could at least gain some useful insights. It turned out I wasn't at all wrong and even managed to figure out a way to use it as a precision ovenised 10MHz source to start playing with experimental GPSDO test setups.

 The other seven 10MHz CQE OCXOs (definitely 12v versions - I still have doubts over the voltage requirements of that first "5V" 13MHz example) are all sine wave output and this is what I'm using in the FY6600-60M. It's rather handy that these are of the sine wave type since I suspect it may have been more of a struggle to get my injection locking module to lock a square wave type via its output pin.

 There are two types of square wave output OCXOs, 'clipped sine wave' and the full blown square wave attained with a separate internal 'squaring' gate drive' IC to give the most perfect of square wave output possible with 50.00% duty cycle as opposed to the former, typically specced for a 45 to 55% duty cycle square wave. Both types, incidentally use dc coupled outputs, allowing them to be directly connected to a logic gate input without any need for biassing the logic gate input to the mid point and adding a DC blocking cap (often not required with sine wave oscillators which typically include such a dc blocking cap anyway - a difference that had left me scratching my head for while when I first started using the 10MHz sine output OCXOs in my GPSDO test builds on solderless breadboards).

 The 'clipped sine wave' type will probably be more amenable to injection locking via their output pins than the fully buffered type which you seem to have. I would suggest you run some experiments (carefully! Use a coupling cap, 100nF should do the trick, to prevent any 5/3.3 volt accidents) before committing to anything based on my design.

Because my ocxo is a square wave can I feed it directly into the 3n502 or will I have to do what you did run it thought the 74hc14 . I don't have a 74hc14 but I have its equivalent cd40106 just the voltage the voltage range differs .  :-+
I am going to make your circuit any way as it looks good . and not to complicated .
Was that the final drawing you up loaded ?

 Since both parts are 3.3v, you can directly connect the OCXO to the 3N502's clk input since, afaicr, it's powered off the same 3.3v supply as the original XO IC.

 The drawing is pretty much the same. All I did was add a note pointing to the 27pF cap to remind me to replace it with an actual trimmer cap (33 or 45pF) so I can trim the optimum value in circuit rather than select on test outside of the module itself. It's obviously not trimmed exactly to suit the actual circuit conditions compared to my select on test setup.

you used 3x 150 ohm loading on your output to the 3n502 PLL  to give the Y connection 50 ohm  :-+
 the only difference is that my OCXO is 20Mhz so I will set the PLL to 2.5x instead of 5 .
every thing else should be good to go .. I have some 10MHz xtals so that part is the same .
the isolation cap that's a ceramic 1uf correct as the drawing was a bit smudgy in places
and 27pf .. not sure I have that odd value .

Using the 3N502 which is taking the place of the original 50MHz XO ic on the main board to multiply your 20MHz OCXO by 2 1/2 to recreate the original 50MHz clock signal to the Cyclone is perfectly fine but since it's now a 20MHz OCXO that needs to be influenced with an injection locking signal, you'll have to double up your external 10MHz reference to match the OCXO's frequency. That's the main departure between mine and your version of this injection locking module before we start considering whether it's actually possible to inject the locking frequency (20MHz in your case) via the output pin route as I did with mine.

 The internal buffer/squaring amp inside your 20MHz OCXOs may offer too much protection against such (normally undesired) external influences for this to work effectively, or even at all. You might have better luck injecting via the Vref pin, the EFC pin or even via the Vcc pin. In view of the filtering on these pins, you'll probably have to use a low impedance drive via a stepdown transformer which will not only reduce the impedance but also provide dc isolation from potentially damaging voltages.

 Given enough drive current into whatever filtering circuit is inside the OCXO on these lines, you may be able to brute force sufficient levels of EMC inside the can, bypassing any such filtering and thereby achieve your goal of influencing the actual oscillator itself.

 The isolation cap to the right of that 27pF cap (a 'preferred value', btw) is actually a 1nF cap. The component itself looks like a green bodied 1K resistor (1000pF), It's not overly critical and I suspect a 10nF might be a better choice (it's just that I had plenty of these 1nF caps to hand ;) )

That choke you used 4.6uH  I can only find 4.7uH .. It will have to do I can't find a listing for 4.6uH or you made it??
But I am read to go for the build ..
Still waiting for my PLL chip will be another week so that will give me time to make Magic smoke.

Thanks RNS

 A 4.7uH inductor is probably close enough. I didn't have any 4.7uH inductors so took an 8.2uH or some such inductor and removed enough turns to drop its value to what the filter calculator had actually called for using my trusty Banggood LC tester (what a Ghodsend that has been!  :) ).

 If you have an LC tester and a small collection of 4.7uH inductors, you will very likely find a 4.6uH in amongst them (the tolerance on such inductors is very slack indeed as I discovered when I started testing a bunch of them that had been lurking in my now rather neglected basement radioshack / workshop for well over thirty years.

 Of course, this won't be relevant at an injection locking frequency of 20MHz :( Even if you were using a 10MHz sine wave output OCXO, you could probably, in view of the 10MHz series resonant Xtal's presence, do away with that inductor and the 2nd 100pF capacitor. The 150 ohm with 100pF RC LPF filter should still be kept to protect the Xtal from being hammered with odd harmonics which could excite a strong third overtone (with associated spurii) response from a Xtal operating in its series resonant mode.

 I reckon you've got quite bit of testing to do with those 20MHz OCXOs of yours before you can figure out the best way (if, indeed there is an actual way) to inject your reference frequency into any of these OCXOs. I've never tried testing this with my one and only 13MHz square wave OCXO so I don't really know just how difficult (or easy) a task this will be. I wish you all the best in this endeavour.

JBG
« Last Edit: May 30, 2020, 04:10:22 am by Johnny B Good »
 

Offline Labrat101

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Hi JBG

I build it as per diagram without the last stage ie the transistor.
This is what I got without any alterations ..
I have not got the PLL yet ..
What do you think is it correct ?? 
The cd40106 was on the 3.3v for test But I think it should go to the 5v . its will operate 0.9 - 15v as per spec sheet .
The time between the Pip & the valley is 4ns exact .
It Had only been running about 20 mins so it ocxo was still stabilizing a bit
There is copper stripping underneath for ground plain .
there are 2 more pics but I got a MAX error  :palm:

i found this but it does not tally with your calculation maybe I'm missing something . (yup a few of my screws )  >:D
http://www.calculatoredge.com/electronics/bw%20pi%20low%20pass.htm
What calculator did you use ??
« Last Edit: May 30, 2020, 03:01:05 pm by Labrat101 »
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Offline Johnny B Good

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 It's difficult to see exactly what you've built onto that 0.1 inch matrix board, so I can only assume that you've assembled a cutdown version using a dog slow cmos version of a 74HC14 to do some initial testing whilst awaiting that pack of 3N502 ICs you've had on order from your supplier.

 The 20MHz pulses coming out of the CD40106 you're using look like just what you'd expect to see out of Old Skool cmos crap substitutes for TTL logic chips. You should be using more modern cmos versions such as the 74HC or 74HCT range (or even the original 74 series if needs must - example: the 74HC193s just couldn't cut the mustard with a 26MHz clock signal in my GPSDO and I was forced to use "The Real Thing", aka an actual 74193, for this task).

 It's well worth downloading and studying the datasheets on any ICs, especially old cmos ICs before soldering any into your test boards (in particular, look at any timing specs - hint: scan down the extreme right hand column of each table to hunt down units mentioning ns or MHz  ;) ).

 I had enough concerns over propagation and transition delay timings at just 10MHz (the 26MHz clock example was just an inescapable consequence of dividing a 13MHz OCXO' square wave output by 1.3 requiring just one "Special IC" in the circuit). You're dealing with a clock speed of 20MHz which makes such dynamic performance of the logic gates used literally twice as important.

 When I was looking for datasheets for a CD40106 IC, all I could find were datasheets for the much slower buffered output versions (B suffixed) quoting typical and max delays at a Vcc of 5v of 140 and 280ns for the TI parts (Intersil only quoted the max values, not bothering to tease its customers with vague promises of a faster typical performance). It looks like there may never have been an unbuffered version and I can't locate where I've hidden my CMOS Logic data book to check on this.  :(

 TBH, I can see you struggling to persuade these 20MHz OCXOs to respond to the injection locking method. That's not to say you won't find a way since injection locking by accident is one of the designer's worst nightmare scenarios, requiring careful consideration to avoid this, including the use of extremely well buffered oscillator outputs to minimise this risk.

 However, you might find it easier to use a PLL to feed a trimming voltage to the EFC pin normally controlled only with a well padded out multi-turn trimpot that's normally used to facilitate manual calibration of test equipment blessed with an OCXO to provide it with an internal highly accurate and stable free running clock oscillator reference.

 In this case, you'll need to effectively disconnect the PLL output's disciplining control voltage feed from the EFC circuit in the absence of a valid external reference signal. This assumes that you don't want to just give in and go for the "Simple Change-over switch and never mind the glitch!" technique. ;)

 I may have needless concerns over this glitchy way of simply using a changeover switch to go between the internal and an external reference but, if nothing else, this injection locking module does obviate the need for such a switch, automating as it does, the whole change-over process to a simple matter of merely connecting and disconnecting the external reference to seamlessly effect the change-over.

 There is a pushbutton switch in my circuit but this is only to effect a change-over between terminated and unterminated mode which would normally be a once in a blue moon operation rather than a regular chore to switch between the external and internal reference clock sources.

 That PLL suggestion does have the merit of allowing you to phase lock an "Injection Locking Immune" OCXO to an external reference, retaining all the benefits of injection locking (glitchless automatic change-over to and from an external reference) so may be a more rewarding avenue for you to follow with these 20MHz OCXOs.

 Anyway, have a think about this before you commit to what might prove in the end  to be an utter folly. By all means experiment with the injection locking idea but be prepared to check out other options.

JBG
 


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