Low cost <1 ppb 10 MHz OXCOs on ebay

[rhb]

There are a slew of references based on the CTI OSC5A2B02 10MHz 5V Square Wave OCXO Crystal Oscillator very cheap (~$20 USD).  After placing in an enclosures to protect against drafts, the two I am testing are holding <0.1 ppb day to day stability once trimmed to the thermal environment.  Bare modules are less than $3, though I don't yet know what I'm going to get.

The one shown  lacks fiber fill to damp airflow and is very stable lying flat, but shifts frequency quite a bit if placed long edge vertical.  Lay it flat again and it's back where it was.  Another filled with cotton balls doesn't care about orientation.

This one will get a mat of fiber insulation and a temperature controller.  The dramatic change in frequency from convection makes keeping a copy of this pointless except as an example of what not to do.

The yellow trace is one of Leo Bodnar's GPSDOs.  The other trace is the OXCO output.  I attached the two screen dumps so you can calculate the frequency difference independently of my 5386A.  I know from experience that when the error is <0.01 Hz I can't possibly get it better.

One of the great virtues of packaging them in a box is the ability to use it with any T&M kit that takes an external 10 MHz reference via a backpanel  port.

Have Fun!
Reg

[james_s]

I see the boards, but I don't see any bare oscillators. I wonder what these came from? Cell sites?

[I wanted a rude username]

They tend to be "gently reworked" off various PCBs as you can see in this photo from an AliExpress listing. The thought of saw-induced vibrations in such a precision part gives me the screaming abdabs.

[SCSKITS]

I have bare boards for these low cost OCXOs here: : https://www.ebay.com/itm/155419526549 if anyone is interested.

Also re-did the 53131A OCXO module (which was originally from the HP design/schematics) but changed out the expensive and sometimes hard to get AD7243ARZ DAC with a less expensive 5V DAC.

ed

[rhb]

 Limited to a 10 s gate, the 5386A is  really not  much more accurate than ~0.1 Hz.  So for serious study I need to develop an appropriate instrument by feeding a GPSDO clock to the timer inputs of a fast MCU dev board.

At the moment I'm leaning towards putting aluminum plates thermally bonded to Peltier devices with old CPU  heat sinks and fans attached for precise temperature control.  The optimal temperature is just high enough to keep the OXCO oven from turning on, avoiding generating  transient thermal events generated by the OXCO heater.

I rather fear I am among the lost as I'm about to see if the fabled <$150 rubidium standards exist.

Pray for my salvation and that I shall be delivered from the debauchery of becoming a Time-Nut. ;-)
Reg

BTW this is the board design I bought though possibly not this vendor.

https://www.ebay.com/itm/144978139139

[ch_scr]

Limited to a 10 s gate, the 5386A is  really not  much more accurate than ~0.1 Hz.  So for serious study I need to develop an appropriate instrument by feeding a GPSDO clock to the timer inputs of a fast MCU dev board.
[...]

If you don't want to have to invent the wheel again (or as a second source sanity check), there is this project on here, just a heads up in case you haven't seen it.

[807]

@rhb...were you able to tune the xtal to 10MHz without modifying the resistors?

As from this previous thread, the module bought by me & others wouldn't tune to exactly 10MHz without modification...

https://www.eevblog.com/forum/projects/cheap-chinese-ocxo-frequency-reference-modules/msg4728044/#msg4728044

[rhb]

@rhb...were you able to tune the xtal to 10MHz without modifying the resistors?

As from this previous thread, the module bought by me & others wouldn't tune to exactly 10MHz without modification...

https://www.eevblog.com/forum/projects/cheap-chinese-ocxo-frequency-reference-modules/msg4728044/#msg4728044

I had no trouble with either of mine.  We'll see when I get the other 3.

The bare modules need power and control voltage.  I can set the two I have to within 0 002 Hz but it still drifts despite batting inside and the unit in a beer box filled with batting.  Generally 0.03 Hz  or less over 24 hrs.  I need to attach an AR488 to log data.

I also need to make a test fixture for the bare  modules with the ability to select modules and automatically set them.  A single LM399 with TL082s for feeding each OXCO a stable Vref.

I'd like to close this thread and shift to the other one.

Reg

[MIS42N]

The bare modules need power and control voltage.  I can set the two I have to within 0 002 Hz but it still drifts despite batting inside and the unit in a beer box filled with batting.  Generally 0.03 Hz  or less over 24 hrs.  I need to attach an AR488 to log data.

The stability of these is more dependent on the stability of the control voltage than the case temperature. The sensitivity to control is around 0.1V/Hz (or about 1 part per million per volt, whichever way you like). So a change of 1 part per billion only requires 1mV change. If the control voltage is around 2V (most are) and the supply is 5V that equates to a supply change of 2.5mV. Most run of the mill regulators like the 7805 change output 1 or 2mV per degree C.

Also from a cold start they drift significantly for an hour then a bit for two days. After two days they are pretty stable. May take a week if just installed (maybe heat from soldering or something?).

For a square wave into 50Ω I use a 74HC04 buffer - see the details around the OSC5A2B02 at https://www.eevblog.com/forum/projects/budget-gpsdo-a-work-in-progress/msg4329907/#msg4329907 - the output of the OCXO is HCMOS so not designed to drive into test leads.

[james_s]

It's pretty well known that crystal oscillators take a while to stabilize after not being used for a while, IIRC it has something to do with the crystal wafer itself outgassing or something. I agree about the control voltage, from looking at the picture my first thought was the cheap little pot used on those boards probably has a lot more drift than the oscillator.

[Datman]

The stability of these is more dependent on the stability of the control voltage than the case temperature. The sensitivity to control is around 0.1V/Hz (or about 1 part per million per volt, whichever way you like). So a change of 1 part per billion only requires 1mV change. If the control voltage is around 2V (most are) and the supply is 5V that equates to a supply change of 2.5mV. Most run of the mill regulators like the 7805 change output 1 or 2mV per degree C.

I made a TCXO using a OSC5A2B02 and a TL431.

[GigaJoe]

"Limited to a 10 s gate, the 5386A is  really not  much more accurate than ~0.1 Hz. "

that not true , this type of counters are second generation, able to measure phase shift between signals, with minimal jitter and 10M source usually are, it perfectly measure extended 11 digits.   in practice im able to compare with 100 and 1000 sec  period with other counters, with the same result.

CETC institute has a lot of documents in PDF  publicity available but i think around 2016 access to the web site was blocked.  as it basically close to military.  i may mistake but as far as remember  OSC5A - AT cut , OC5SC - SC cut, with better long therm.

12volt OC12SC36 - has better volt sensing circuit, in my practice approx 0.3mV to adjust greater accuracy. and that as well force to use very well stable source of adjusted voltage.  the best result i got  when voltage source thermally connected to OCXO case,   basically thermally stable,  with some additional thermal isolation i had drift in -2-10 \Y (really no. remember, but perfectly fine for 8d direct counter) as well it help in  1-decrease power consumption. 2-much better temperature control. 3-decrase jitter due to temperature deviation.

"cheap little pot" - use the same, not affecting at all,  in a correct circuit   adjustment has to be a small fraction of total regulated voltage,  so ideal rough adjustment inside the heated chamber, and superfine outside.

[rhb]

The stability of these is more dependent on the stability of the control voltage than the case temperature. The sensitivity to control is around 0.1V/Hz (or about 1 part per million per volt, whichever way you like). So a change of 1 part per billion only requires 1mV change. If the control voltage is around 2V (most are) and the supply is 5V that equates to a supply change of 2.5mV. Most run of the mill regulators like the 7805 change output 1 or 2mV per degree C.

I made a TCXO using a OSC5A2B02 and a TL431.

Pray tell, tell us more.

[Datman]

It's very simple:
The ATtiny85 makes the LED flashing at three different frequencies according to the temperature. When it is stable, the working temperature has been reached.

[807]

It's very simple:
The ATtiny85 makes the LED flashing at three different frequencies according to the temperature. When it is stable, the working temperature has been reached.

Why did you increase the TL431 reference voltage to 4v? Did you find that you couldn't adjust the xtal to 10MHz using 2.5v?

Most of the results on here for the xtal ref voltage seem to be less than 2v.

[Datman]

0 to 4V -> -2 to +2 ppm:

[MIS42N]

I made a TCXO using a OSC5A2B02 and a TL431.

I looked at the specs for the TL431, it did not seem to be any better than a run of the mill LDO regulator but used for a different purpose. Might as well take the divider straight off the +5V supply. Or did I miss something.

If the OSC5A2B02 has been used frequently, it takes about 15 minutes from cold start to reach some form of stability. The first 3 minutes it can be in error by more than 10Hz. After 15 minutes it is less than 1Hz out, usually around 0.1Hz. It will change frequency if its orientation is changed. Tip it upside down and then right way up, it can settle at a different frequency. So once it is set up it is not a good idea to move it.

[james_s]

The TL431 has been around for ages, and it's a shunt regulator which is designed as a voltage reference. If you use a power rail as a reference then your reference is affected by other loads on that rail.

[MIS42N]

The TL431 has been around for ages, and it's a shunt regulator which is designed as a voltage reference. If you use a power rail as a reference then your reference is affected by other loads on that rail.

Of course!! I made that comment late at night without too much thought. In fact I had the problem with my GPSDO design, and solved it by running the OCXO and its control voltage off a separate LDO. The OCXO provides a fairly constant load so using its +5V also for the control voltage source is OK with the advantage that the OCXO has a stable +5V supply. I also made provision for a precision voltage reference but it didn't yield much improvement so usually left off.

[GigaJoe]

TL431 can change output voltage up to 50 millivolts by internal ageing process ... it basic, extremely cheap reference. you not get maximum potential from OXCO using this type of reference.  I had some LM336 -5  thermally connected , as better version of TL ,  and even after 3-4month that has not enough stability , the frequency shifting as LM336  drifting ....   for a best result overall drift should be as low as possible.

I suggest something LT1021 . LT1027 ,  or similar  thermally connected to OCXO,   plasic  ok, used one ok  ... 
https://www.ebay.com/itm/324030185416

[rhb]

[snip]

I suggest something LT1021 . LT1027 ,  or similar  thermally connected to OCXO,   plasic  ok, used one ok  ... 
https://www.ebay.com/itm/324030185416

The voltage reference should be in complete thermal isolation  from the OXCOs as should be the voltage dividers for each OXCO.  These should be TL08x or similar voltage followers so there is no discernible load on the reference.

Each OXCO should be in its own oven set so the internal heater never turns on.  That will minimize thermal gradients.


Have Fun!
Reg

[Yrrah]

For those interested: this weekend my ready made board with a CTI 10.0 MHz OCXO by BG7TBL arrived. It looks all brand new but I guess the OCXO is salvaged from an obsolete system. I made some phase noise measurements with my home brew PN system (DG4RBF, UKW Berichte and Audiometer by DG8SAQ). In all cases the reference oscillator is a HP10811A as it is EFC controlled. All components are battery fed. As a sanity check I measured a Wenzel 501-08772 first. Then I measured an Isotemp 131 OCXO and the CTI (OSC5A2B04). Warm-up time > 30 min. The results are attached. The Wenzel is my "gold" standard: PN as per datasheet: @ 100Hz = -155 dBc, @1kHz = -165 dBc and at 10 kHz also -165 dBc. The HP10811A measures: @100 Hz -154 dBc , 1 kHz -163 dBc and 10 kHz -164.5 dBc. From brand reputation: both are probably even better than the specs. There is not much difference between the two. Pretty much in agreement with HP spec. I am not claiming accuracy within 1 dB. And if the difference is small no distinction is possible. The Isotemp measures: @ 100 Hz -149 dBc, @ 1kHz -155 dBc and @ 10 kHz -156 dBc. The CTI: @ 100 Hz -143 dBc, @ 1 kHz -154 dBc and @ 10 kHz -158 dBc. Quite close to one another and the distance to the 10811 is large enough for the numbers to be ok. Any one to confirm or to dispute these figures?

[Yrrah]

A couple of weeks ago I got 4 more CTI OCXO's (5A2B02), nicely removed form whatever system. Time for some additional noise spectra measurements. I made a test-fixture to accommodate the DUT's. No good looks but effective. Power (+5V) is provided by a 7806 followed by an RCRC filter (R=2.5 ohm, C=1000uF, 105C). In UKW Berichte (4/2022) I have shown that a good filter behind a mediocre (noise point of view) voltage regulator can give quite good results. The EFC voltage is generated by a LT3045 set at 5V. You need a range of about 1.5 - 2.2 V so I took a 500 ohm multiturn and about 1 kohm to ground and 2.2 kohm to +. The DUT is embedded in some sort of foam for thermal stability. Not quite good visible at the picture. Between cover and OCXO is also foam. This way the current draw drops to about 170 mA, once warmed up. Some additional caps here and there and that's it. No output filter, just the square wave. Before the noise measurement some basic tests were performed and the spectrum was observed. Just some soldering to exchange the DUT.
The photo shows the measurement set-up. Everything is battery fed. Exactly the same as described in previous post. The DUT is followed by a 5 dB attenuator.
The results are shown in the third picture (S1P files from Audiometer fed to Octave script to generate graph). No 5 is the 5A2B04 (on ready made pcb, refer to previous post). You clearly see some statistical variance between DUT's but they are all pretty good. No1 is best but the differences are small. The reference (HP10811-60111) can be seen in the previous post still better than any of the CTI's. Out of curiosity I measured no3 with a Minicircuits LPF: no difference. Now I'd like to see Adev measurements, well that's possibly for the future.

[rhb]

Thanks for taking the time to post these.  I'm hoping to buy a tinyPFA and run Adevs as soon as R&L stocks them.

For $3 each I think they are fantastic deals.  Every test that I've seen shows that they are quite good.  Not the best,  but likely much more stable long term because of aging.

Reg

[Yrrah]

Well, I think this kind of info/data is easier to retrieve here. Over the last two days I measure about 20 mHz drift (max) of OCXO no3 in test fixture. Measured with my HP5345A counter (always on, internal HP10811 clock). Nice stuff indeed. 
Harke

[rhb]

Do you have a GPSDO?  My testing over several days with a pair of the PCB versions, the OXCO in my HP5386A and  a Bodnar 2 output GPSDO viewed on a DSO triggered on the GPSDO showed the CTIs were as good and possibly better than the OXCO in the 5386A.

I've been testing RF cables from bydpete on ebay.  I've got 10x $ value in additional cables coming.  My 2nd batch of 10 CTI units is making its way slowly in my direction.  I also ordered a bunch of multiturn dividers.  I am going to attempt to build a fixture that will let me run 5-10 units at once and switch between units automatically over a long period of time.

I have never been able in any of my attempts to set an OXCO to exactly match the GPSDO.  If I have an instrument open I usually attempt to retrim the OXCO as almost all my HPAK kit has the OXCO option installed.

That experience over the span of 5-6 years has convinced me that without an electronic means of setting the control voltage it is impossible to set exactly to 10 MHz.

If  the phase noise is Gaussian, combining 4 OXCO outputs *might*  cut the phase noise in half.  No idea yet if that is possible, much less how.  Just an interesting idea at present.  At normal OXCO prices it would be cheaper to add  a GPS receiver.  But  at $3 that changes.  If it's possible to cancel phase noise adding a GPS receiver might yield a significantly more stable reference with 3 dB lower phase noise than a single OXCO for very little additional cost.

Have Fun!
Reg

[WatchfulEye]

I've found the CTI OCXOs really impressive for the cost.

The 2 main things that separate them from more expensive OCXOs are:
unpredictable retrace (can restabilise at up to 5 ppb from where they stabilised before) as well as severe frequency drifts over the first 12-24 hours, gradually stabilising over the next few days.
High temperature coefficient (the one I've best characterised has a -500 μHz/K coefficient).

Once stabilised, the performance is very impressive, however.

Here are 2 examples of stability against my reference of another free-running OCXO, a trimble 73090 off aliexpress. This also gives excellent performance and this particular one is in a thermally isolated box and has been running for months, and shows essentially zero aging against GPS.
One is with the OSC5A2B free running, and the other is with EFC temperature compensation.

Note to the eagle eyed - the TC does not appear to be -500 μHz/K, but that is because the ambient temperature is plotted, not oscillator enclosure temperature. Because the OCXO is temperature controlled, it has a stabilising effect on the temperature in the enclosure, typically reducing temperature swing amplitude it by about 50% compared to ambient.



 

[MIS42N]

The OSC5A2B02 is more sensitive to variations of the control voltage (EFC) than more expensive OCXOs. I've characterised quite a few and they are around the specified 1ppm/V. Which is 1 part per billion per millivolt. Most run of the mill regulators are in the 1mV/C range so for better results the source of the EFC becomes important. Some design is required to avoid small voltage variations in the earthing system. The reference for the EFC source needs to have the same earth as the OCXO. I made a PCB with a layer of copper as the common earth, there was enough stray current to create small voltage differences (microvolts) between the OCXO earth and the EFC source earth. It had a noticeable effect.

[Yrrah]

Already some nice work done. Kudos! I had OCXO no 3 running for several weeks (24/7) in my test fixture and I just noticed the frequency did not change within 20 mHz. This on my HP5345A counter with a HP10811 OCXO. Always plugged, of course. No scientific accuracy claimed of course but indeed good evidence these OCXO's are really good.
Br,
Harke

[WatchfulEye]

I've had a chance to do some additional measurements, and I was a bit surprised by the results.

The measurements shown are my OSC5A2B02 based GPSDO vs a freerunning OSC5AB202 and a rather more expensive, freerunning trimble 73090 DOCXO.

In green is the OSC5A2B02, and in black is the 73090. Noise floor of my frequency counter is shown in blue. The OSC5A2B02 clearly has substantially better short term stability.

The medium (500-2000 s) tau are not reliable on this plot, because the GPSDO was locked and GNSS noise in my setup is substantial. However, at very long tau, the drift and temperature sensitivity of the OSC5A2B02 is clearly visible compared to the double oven trimble.

[rhb]

I've not been following EEVblog lately, but it confirms most of my observations.

I received  a tinyPFA from R&L and will set that up soon.  I don't have proper environmental control or monitoring and won't for some time while I set up a new lab space.  I'm building a 7 bay rack!  Bit of a TEA binge :-)

A very limited error budget analysis from mains to OXCO shows that PS noise is  a significant limiting factor.  The 20 uVrms noise of an LM399 is 0.02 ppb/s.  That figure requires *no* noise on either the LM399 or OXCO supplies.

I've moved posts of my work to the qex@groups.io list as I had mentioned these on several lists and it became too confusing.

My immediate focus is the PS as that is critical to my goals.  At 0.001 ppb/uV sensitivity getting to 0.01 ppb/yr is going to require very careful environmental and EMI control in addition to active compensation for aging of 4 OXCOs.  Ultimately I plan to heterodyne the OXCO outputs and use a zero crossing detector to get <0.001 ppb resolution.

I'm going to visit an HVAC shop today to have a desktop box made which will get insulated with Peltier thermal stabilization and shielded feedthrus, etc.

Have Fun!
Reg

Edit:  BTW before someone decides to jump up and down about the brutally difficult voltage stability problem that 0.01 ppb/yr implies I'd like to note that after following Ken Thompson's "When in doubt, use brute force." rule I plan to throw everything I know about DSP at the problem. I'll also be selecting 4 OXCOs from a batch of 20 with the intent of deliberately exploiting variations among 4 devices.  For example, if I know that each OXCO has a different response to uV level changes I intend to exploit that as a means of estimating the voltage variation and adjusting system.

In short, this is a very difficult project which I expect to span several years and may end in failure.  Were that not the case it really wouldn't be very interesting.  The only thing I know well is empirically estimating the aging rates and basic knowledge of the relevant factors.

[tszaboo]

So I got a few of these OCXOs because I clearly have a mental issue doing all the projects at the same time.
Does anyone have a PCB design for this?

[alligatorblues]

I rather fear I am among the lost as I'm about to see if the fabled <$150 rubidium standards exist.

Pray for my salvation and that I shall be delivered from the debauchery of becoming a Time-Nut. ;-)
Reg

BTW this is the board design I bought though possibly not this vendor.

https://www.ebay.com/itm/144978139139

For USA buyers, I have 2 rubidium standards. I'll put them in FS if needed. But no nation permits importation of radioactive substances through the post. I can only ship them in the US.

[807]

So I got a few of these OCXOs because I clearly have a mental issue doing all the projects at the same time.
Does anyone have a PCB design for this?

This guy designed a PCB, but didn't provide the files, or put his design in the shared section of PCBway:-

https://www.pa7elf.nl/en:projects:10_MHz_ocxo_frequency_reference

As I have a few Racal Dana 199x frequency counters, I bought a few of these PCB's from OSHPark. They are specifically for the 199x counters though:-

http://syncchannel.blogspot.com/2016/02/ocxo-upgrade-for-racal-dana-199x.html

[Kean]

So I got a few of these OCXOs because I clearly have a mental issue doing all the projects at the same time.
Does anyone have a PCB design for this?

What type of PCB design?

I've been playing with this GPSDO that uses this same OCXO, and I bought 10 extra ebay OCXO modules for some reason (well they were pretty cheap).
https://www.eevblog.com/forum/projects/budget-gpsdo-a-work-in-progress/

As I have a few Racal Dana 199x frequency counters, I bought a few of these PCB's from OSHPark. They are specifically for the 199x counters though:-

http://syncchannel.blogspot.com/2016/02/ocxo-upgrade-for-racal-dana-199x.html

Oh, nice!  I also have a pair of the 1992 frequency counters, so that is 2 of my extra OCXOs accounted for. 

[tszaboo]

So I got a few of these OCXOs because I clearly have a mental issue doing all the projects at the same time.
Does anyone have a PCB design for this?

What type of PCB design?

From what I've seen you need a reference voltage, a potentiometer or a DAC+MCU to make the control voltage and maybe a buffer for the output?
I think I can throw this together in a hurry, but I was just wondering if someone has PCB for it. Probably even breadboards would work.

[Kean]

Yeah, see that GPSDO forum topic I linked to
And https://github.com/ajcashin/budget-gpsdo

[MIS42N]

Yeah, see that GPSDO forum topic I linked to
And https://github.com/ajcashin/budget-gpsdo

You remind me, I really should clean that up. If anyone is up for it, the PCB could do with a redesign as there is some interaction between the OCXO circuit and the PIC/other bits circuit. I thought giving each its own LDO would be sufficient, but it appears having a common ground plane is a problem. And since places like JLCPCB can populate a board as well an SMD/through hole version would be nice - SMD for the common bits and through hole for the CPU and OCXO (and whatever uncommon bits not in JLCPCB's catalogue).

[vindoline]

Thanks to Reg for pointing these OCXOs out! I wanted to let people know that I've used one to make an easy GPSDO reference https://www.eevblog.com/forum/projects/yet-another-diy-gpsdo-yes-another-one/msg5064550/#msg5064550 as well as add high stability options to my Racal Dana 1992 and HP 3325B. The GPSDO was used to calibrate the 1992 and 3325B.

[Andrew_Debbie]

The stability of these is more dependent on the stability of the control voltage than the case temperature. The sensitivity to control is around 0.1V/Hz (or about 1 part per million per volt, whichever way you like). So a change of 1 part per billion only requires 1mV change. If the control voltage is around 2V (most are) and the supply is 5V that equates to a supply change of 2.5mV. Most run of the mill regulators like the 7805 change output 1 or 2mV per degree C.

I have the OSC101 variant.   It works.    It uses a 78M05. The thing is sensitive to input voltage.  As you might expect, small changes to the input voltage will change the frequency by several tenths of a Hz.   

For my purposes the OSC101 is often good enough, but it isn't a good design.

[David Hess]

You remind me, I really should clean that up. If anyone is up for it, the PCB could do with a redesign as there is some interaction between the OCXO circuit and the PIC/other bits circuit. I thought giving each its own LDO would be sufficient, but it appears having a common ground plane is a problem.

A single point ground to remove return currents from the signal ground may be enough.  This is one of those cases where depending on the level of precision required, a ground plane is not a panacea.

Alternatives include using using a difference/instrumentation amplifier to remove the common mode (common/ground) error voltage, or driving the control signal using a current with local load resistor to convert the current into a local voltage.

[Andrew_Debbie]

I've been running mine for about 30 hours  connected to my Racal-Dana 1998.    The 1998 is uncalibrated but has  Option 04B, the high-stability ovened oscilator. 

For the past day or so it has been ±4 counts of 10.00000200MHz.     Not bad considering the set up.  I have no idea how stable the 1998 is.  I see a GPSDO in my future.   I just ordered 5 of the OSC5A2B02 pulls from a seller on AE. 

[ZhuraYuk]

Bought 5 pieces OSC5A2B02  at aliexpress,  https://www.aliexpress.com/item/1005006457029106.html.
Three had horrible jitter, were not usable. Avoid buying these.

[Andrew_Debbie]

I just recieved the sz-plaza dot com rev.0.0.2 OXCO module.   At first glance it is better than the OSC101.  I paid $12.59+VAT (uk tax) for the complete module.


The LDO regulator + LT1009 reference makes the board far less senstive to input voltage changes and alows a wider operating range.   

[807]

I just recieved the sz-plaza dot com rev.0.0.2 OXCO module.   At first glance it is better than the OSC101.  I paid $12.59+VAT (uk tax) for the complete module.


The LDO regulator + LT1009 reference makes the board far less senstive to input voltage changes and alows a wider operating range.   

Could you set the pot to get it to oscillate above & below 10MHz? I, and a few others, had to modify the resistor network, as in this thread...

https://www.eevblog.com/forum/projects/cheap-chinese-ocxo-frequency-reference-modules/

[floobydust]

807, they now ship sz-plaza boards (REV:0.0.2) with a 200kΩ (204) trimpot which gives a V_CTRL 1.95-2.15V span.
But it did nothing, that I could measure to change frequency for the board I have.
*Note my freq. counter(s) are uncalibrated until I get the GPSDO finished, hopefully it is reading a bit high as you will see below.
Bypassing the trimpot, I get around 31Hz adjustment span for 0.14Hz/V:

Code: [Select]

10,000,048 4.543 V +48 Hz 1.6ppm up from 032
10,000,032 2.1556 V trimpot max. +32 Hz
10,000,032 2.125 V
10,000,032 1.9596 V trimpot min.
10,000,022 0.4006 V +22 Hz
10,000,017 0.2017 V +17 Hz

I'm not sure if the offset is my counters' cal or an issue with the module. CTI OC5SC25 (17022)
OSC5A2B02 module spec. is nominal 2.0V +/-2.0V for -1.0ppm to +2.0ppm

The LDO LM2940CS-5.0 is shit quality, line regulation is poor 4.75-4.85V finally up to 5V with 10V in but then it runs warm. It has terrible line regulation, not a great clone. Next I'll try disconnect the sine-filter and see if it is loading things.

[807]

Bought 5 pieces OSC5A2B02  at aliexpress,  https://www.aliexpress.com/item/1005006457029106.html.
Three had horrible jitter, were not usable. Avoid buying these.
(Attachment Link)
(Attachment Link)

Did you try connecting decoupling capacitors directly on the Vcc & Vref pins to GND on the module?

[KedasProbe]

I bought 2 of these via amazon, different sellers.
I also read that people had to change a resistor to get it in range but I had no such problem with mine. One had a red led and the other a blue led, one with a low OCXO serial number and one with a high one.

I power both with 6V (5V is too low, spec is min. 7V but uses a little more power)
Changing from 7 to 13V has an impact on your fine-tuning so decide on your power supply voltage.
Also the 50ohm load has an impact on your fine-tuning so make sure you have the correct load attached.

[Electro Fan]

I bought 2 of these via amazon, different sellers.
I also read that people had to change a resistor to get it in range but I had no such problem with mine. One had a red led and the other a blue led, one with a low OCXO serial number and one with a high one.

I power both with 6V (5V is too low, spec is min. 7V but uses a little more power)
Changing from 7 to 13V has an impact on your fine-tuning so decide on your power supply voltage.
Also the 50ohm load has an impact on your fine-tuning so make sure you have the correct load attached.

If you feed them into a counter what does the counter say for the red unit and the blue unit?

[metrologist]

Bought 5 pieces OSC5A2B02  at aliexpress, 
Three had horrible jitter, were not usable. Avoid buying these.

That's terrible. I bought several off ebay years ago, put one in the Lars GPSDO setup. I should test the raw ocxo

[floobydust]

I'd noticed a 25kHz sine amplitude-modulation (envelope) at the 10MHz output- but thought it's just my scope aliasing.  It's on my list to see if this is a scope artefact due to lower sweep speed, or if the module has a parasitic oscillation.

Those pictured modules,
The one on the left has newer 200k trimpot, red LED, possible better NS LDO.
The one on the right 100k trimpot, blue LED, crap quality LDO.

I've got a 200k trimpot, blue LED and crappy LDO. They'll use any parts in these as some are not critical.

[Electro Fan]

Thanks to the comments in this thread I thought to re-look the power supply setting for the Amazon OCXO.  Previously, I had the PS set at 12V and had tried various trimpot settings but could never get the counter to show better than about 10,000,000.7 Hz. 

After reading this thread I decided to try around 5V while also twiddling the trimpot.  The BG7TBL FA-2 counter is taking it's ref from a BG7TBL GPSDO (same as it was when I was operating the OCXO at 12V).  It's hard to know what exactly is causing what, or more specifically, it's hard to know what's accurate and what just looks good, but by dropping the voltage on the power supply to 5V or somewhat lower the Amazon OCXO was able to improve it's performance, at least according to my particular testing configuration.

Main point is that the voltage feeding the OCXO can have an order of magnitude or more impact on the OCXO's performance, I think.  The spec printed on the board says DC7-13V@1A; at 4.64V and 292mA it seems happy.

[GigaJoe]

ah ...   you have a board ....   I assume it was just that metal can only.
about that thingi  i can not comment , honestly ...   as it unclear how it constructed ..

i build a while ago , like 4 years ago ,F ref , on the same OCXO can,  it was significantly thermally isolated, consumed 25 ma
after a while, year or so in ON state , drift was ... hm ... in 4 month approx. , from  precise 10 ...  to around 9.999 999 998 5
sooo  basically 5 10-8  per year  around  ... ( i'm right?)

received today OSC5A2B02, was curious about jitter .... seems nothing ...
I may consider , super duper high jitter was incorrect measurement :
i'm wait 60 seconds , till snapshot , that 7th rise from the trigger


forgot to say .... that high P-P,  due to GPSDO, reference , as the circuit truing to constantly push-pull OCXO adjustment , if you run fa-2 for at least a week , internal oscillator would be reasonable steady, and hook gps to input, you may see as 2 last digit constantly jumping up or dowm,   merely depend on gpsdo algorithms adjustment  ...

[Electro Fan]

forgot to say .... that high P-P,  due to GPSDO, reference , as the circuit truing to constantly push-pull OCXO adjustment , if you run fa-2 for at least a week , internal oscillator would be reasonable steady, and hook gps to input, you may see as 2 last digit constantly jumping up or dowm,   merely depend on gpsdo algorithms adjustment  ...

I think the GPSDO does constantly adjust up and down but I'm pretty sure what you saw above for Pk-Pk with the Amazon OCXO is primarily from the Amazon OCXO/board.

Below is the same FA-2 counter (getting it's ref from the GPSDO) taking a 10 MHz input from an Agilent generator (also ref'd to the GPSDO).  Not so much Pk-Pk.  I think this indicates that the GPSDO can be reasonably steady.  If need be I can probably find similar results from measurements made over longer durations.

This stuff can seem like an endless rabbit hole, especially if you don't have a rock solid reference point but after lots of rabbit hole experimenting, I think the BG7TBL GPSDO and counter make for some pretty decent measuring.  Having said that I'm open to figuring out how to measure more accurately and how to be more certain of the accuracy.

Slightly off topic, but one of my motivations (reasons for making and posting the measurements) is to persuade any observers from Siglent that as great as their oscilloscopes are they could be even greater if they offered more models with a 10 MHz Ref in.  When a $14 retail OCXO board can provide 1-2 orders of magnitude better than what comes with a $1k-$3k oscilloscope why not provide a Ref in?  And with a decent GPSDO the performance could be even better.


- no doubt the last 3 digits (as in the 012 7 Avg) will jump around but at this point I think maybe it's good enough; if I could persuade myself that these frequency numbers are accurate at this level of precision I'd be ready to move on to trying for better measuring of amplitude , and of course phase

[Andrew_Debbie]

My LBE-1420 GPSDO arrived today.   I'll be checking my "blue light special"  soon.    It does not appear to be overly sensitive to input voltage.   Maybe this one has somewhat better parts.

[GigaJoe]

i fry one one of my counter ..   and looking around got BG7TBL FA-2 with 6 buttons.

FA-2 design: in use ATmega328P microcontroller. 
this is 8-bit microcontroller with 2K RAM,  no float operations in hardware
to calculate float value, you need a library that can simulate float on 8bit integer ...  float 4 bytes
for a precision of 7 decimal point to show on display ;  you need double float  in calculation ;  double float 8 bytes

connection OUT to IN - i do observe flickering in LSD  - I may assume it errors in calculation. as the rest are constant. and error due to 8bit INT to FLOAT library

in averaging mode we see 7 decimal point, but even with OUT to IN mode,  everything after 5th digit are random ...  basically noise

so  looks like , there no double float precision, limited memory means no room for precise calculations.
consider that , a may assume that precision for single measurement as calculated value would be 5 decimal point ±2 LSD. 

averaiging: my guess averaging window somewhere 10 numbers,  so running N 500 - no value ( and no space in memory) , as it shows last 10 averaging.
with 5 decimal points,   the rest basically noise  ....

on opposite side , if we have reference 10Mhz , to measure with precision .00000  we need to detect phase shift  better then 100nS / 100000  = 0.01nS , 10pS , I have no any experience with intel altera MAX II EPM570 CPLD  that in use for this counter ....

I may wrong in my conclusions ....  but atmega ...  really?

[Electro Fan]

i fry one one of my counter ..   and looking around got BG7TBL FA-2 with 6 buttons.

FA-2 design: in use ATmega328P microcontroller. 
this is 8-bit microcontroller with 2K RAM,  no float operations in hardware
to calculate float value, you need a library that can simulate float on 8bit integer ...  float 4 bytes
for a precision of 7 decimal point to show on display ;  you need double float  in calculation ;  double float 8 bytes

connection OUT to IN - i do observe flickering in LSD  - I may assume it errors in calculation. as the rest are constant. and error due to 8bit INT to FLOAT library

in averaging mode we see 7 decimal point, but even with OUT to IN mode,  everything after 5th digit are random ...  basically noise

so  looks like , there no double float precision, limited memory means no room for precise calculations.
consider that , a may assume that precision for single measurement as calculated value would be 5 decimal point ±2 LSD. 

averaiging: my guess averaging window somewhere 10 numbers,  so running N 500 - no value ( and no space in memory) , as it shows last 10 averaging.
with 5 decimal points,   the rest basically noise  ....

on opposite side , if we have reference 10Mhz , to measure with precision .00000  we need to detect phase shift  better then 100nS / 100000  = 0.01nS , 10pS , I have no any experience with intel altera MAX II EPM570 CPLD  that in use for this counter ....

I may wrong in my conclusions ....  but atmega ...  really?

Thanks for the info based on your examination of the counter and GPSDO designs.  Sounds like there are extra digits that are random.

I don't have a good way (that I know of yet) for measuring or comparing against a baseline that is known to be accurate.  So I'm on the lookout for something that could help determine what's what.

I happen to have a Leo Bodnar miniGPS that I use to provide a 49,152,200 Hz clock signal to a radio, or at least I that's the designated frequency.  I fed that signal to the FA-2 (which is taking it's 10 MHz ref from the BG7TBL GPSDO), and got the results shown below.

If I understand you correctly, maybe anything over 10 samples is really just the average of the most recent 10 samples?  And you think 5 places to the right of the decimal might be relevant?  Thanks for any help in clarifying this. 

Attached are the LB specs.

PS, slightly off topic, but the more I look at the designs of all sorts of stuff (from clocks to AI) the more I appreciate the power of floating point and the need to use it appropriately

[GigaJoe]

the second though that  atmega role not as calculator , but display and buttons manager only,   then all measurement and calculations fall to  intel altera MAX II EPM570 CPLD chip. so my conclusion is incorrect ...

in this case how precise it ....  i cant tell ..

[Electro Fan]

the second though that  atmega role not as calculator , but display and buttons manager only,   then all measurement and calculations fall to  intel altera MAX II EPM570 CPLD chip. so my conclusion is incorrect ...

in this case how precise it ....  i cant tell ..

I appreciate and admire the ability to have second thoughts and to keep exploring, not to mention your newest idea is more encouraging regarding the likely efficacy of the architecture

- further into the rabbit hole we go 

[Electro Fan]

Nothing like OCD in the rabbit hole.

I recorded 29 consecutive measurements (with 10 second gates); #350 within the series is shown below.  I entered the 29 consecutive current reads ("Fin") and the average reads as shown in the attached spreadsheet.  I can't tell how many reads go into the average calc but I think it's more than the most recent 10.  Maybe someone with a FA-2 can figure it out.

[Electro Fan]

The previous post used several short BNC cables (with inline connectors) plus a couple BNC to SMA adapters.

This one connects the LB GPSDO to the FA-2 with a single 15' SMA to SMA cable.  Much less Pk-Pk variation.

Might have been some reflections at the several adapters in the prior configuration?

Another variable is the ambient temperature as the AC cycles on and off.

All that said, I think this shows that the BG7TBL FA-2 with a ref in from a BG7TBL GPSDO and the Leo Bodnar MiniGPS as the signal input are pretty happily working together to produce what I think are reasonable results.  I realize "happily" and "reasonable" are ("substantially") more qualitative than quantitative - but if anyone wants to suggest some other tests, please feel free to do so.  Thx

[GigaJoe]

doesnt work on random ..

so it def. simple averaging, my calculation match with device , N=10, N=20 , then i give-up

and my has gate 10mS
now only last 2 digits changing ...


with N 1000 or more , it def. not atmega
fun thingi :

Gate 0.01S  N=32000  .994 486 3
Gate 10S     N=10       .996 288 8

if gave possible do variable , it would be really awesome
and seeems yes, averaging not equal precision ..

[Electro Fan]

Update:

I tried a couple more Amazon 10 MHz OCXOs.  One happened to have a blue Led, the other a red Led like the first one I tried (see previous posts).

If you try these, I think it would be handy to have a counter that gives you some reasonable confidence and that has more digits than less to the right of the decimal point (even though we know resolution does not = accuracy; presumably your confidence inspiring counter is reasonably in the ballpark and the extra digits will help you see the rate at which things are going up or down - kind of like having an analog DMM but here we don't have a needle on a dial so we're just watching the digits go up or down and the rate at which they are moving).  For this process I find that a 1s gate gives you a feel for what's happening at what rate. 

When you first set up the OCXO it will take some time to warm up and settle down (maybe a half hour or more).  Once it seems to have settled on your counter, experiment with the trimpot to determine which direction adds resistance vs removes resistance - just give it a turn or two and see which way the counter moves.  After you are sure you know which direction adds resistance/decreases resistance and which way the counter moves accordingly as you do that, quit playing with the trimpot.  If you turn the trimpot too far you will run out of scope.  So after your direction confirming testing you want to start the dialing-in process from near the midpoint of the trimpot.

The next step requires a decent power supply where you can control voltage, and current to at least a milliamp.

At this point, you can experiment with some safe but clearly sufficient constant current (1 amp per the board, or less) while changing voltage from about 4.5V to 12V (the board says 7-13V).  Changing the voltage is unlikely to have much if any impact on the performance you see on the counter, at least that I observed but my tests were all pretty short term. 

Now that you have the the voltage set (maybe at 5V or even less) it's time to adjust the max current.  If the counter shows less than 10 MHz, add a milliamp or two and the OCXO will run faster, as you should see on the counter.  If the counter shows more than 10 MHz reduce the current by a milliamp or two and the OCXO will run slower.  You have to be patient with this process or you will overshoot the mark.  You might/probably won't be able to get the counter within much more than a 0.1 Hz of the target 10 MHz by just adjusting the power supply.  I found that 1 mA moves the frequency by more than 0.1 Hz.  So once you get the counter reading as close as you can with the PS adjustments then you will have to start adjusting the trimpot.  (EDIT:  I think the mA to 0.1 Hz relationship might change the longer the OCXO has settled in.)  In any event, the trimpot adjusting process is not the most confidence inspiring thing but it's pretty much all that's left other than the PS.

My main learning (or at least what I think I learned) is that regulating the current is pretty important to being able to control the OCXO's frequency.  Another thing that I'm sure adds a variable is the ambient temperature in your room.  I know from previous experiments that a degree C or F can be enough to change resistance in a resistor by a a few milliamps.  (I learned this by experimenting with a short piece of copper wire and doing some 4-wire Kelvin clip readings).  The point here is that when trying to dial-in a milliamp you could be chasing more than the milliamp of frequency-varying current if the resistance of your circuit is changing due to the ambient temperature changing.  Every time you touch the board to steady it while adjusting the trimpot you will probably heat up the board, which can add some confusion to the trimpot adjusting process.

Feel free to ask questions or point out any thing I got wrong - it's possible I missed on some of this - it's all a learning journey.  Happy metrologying.

EDIT:  After spending more than a couple hours trying to dial-in 10 MHz by adjusting the current coarsly with the PS and more finely but without much luck on the trimpot, I came up with two ideas:
1. Buy a new PS that can set current to at least a tenth of mA (within 100 microamps) - but a quick look-see indicates that would be expensive, so I moved on to:
2. Turn on the air conditioning and within two minutes I can lower the temperature and the frequency sufficient to drop 0.2Hz.  I think idea #2 while not easy to control overshoot is going to be the more cost-effective approach.

[KedasProbe]

I compared my two OCXOs to each other.
It wasn't very repeatable so I added two curves B and D
the timelab files are attached.

Conclusion is what we already knew, below 10 sec the cheap OCXO is more stable than the leo bodnar GPSDO.

I checked power supply influence but it's below 2mHz per volt.
That is basically how much change there was in 1 hour. (keep in mind I compared them to each other)

[Andrew_Debbie]

I just recieved the sz-plaza dot com rev.0.0.2 OXCO module.   At first glance it is better than the OSC101.  I paid $12.59+VAT (uk tax) for the complete module.


The LDO regulator + LT1009 reference makes the board far less senstive to input voltage changes and alows a wider operating range.   

Could you set the pot to get it to oscillate above & below 10MHz?

Yes, I can get it to oscillate on either side of 10MHz.       I connected my Racal-Dana 1998 counter to a Leo Bodnar LBE-1420 and let it run over the weekend.   After a day my counter settled at 10MHz +.04Hz.

I am not going to adjust my counter.  I might make it worse.

Now that I have verifed the counter, I'll start doing some check tests on my "Blue Light Special".     

Input voltages between 6V and 7V don't make any short-term change to output frequency within the resolution of my counter.      This one must have a halfway decent LT1009 voltage reference.     

I'm going to let it run for a few days.   

[Electro Fan]

I'm probably far down the knowledge and experience curve from most or all of the posters here but fwiw, I find that adjusting the Power Supply voltage between 4.25V and 12V is only somewhat interesting and impactful; more interesting and impactful is directly controlling (by limiting) the PS current available to the eBay OCXO board.  More current causes the OCXO to run faster, less current slower.  Also, the current seems to impact the OCXO board temperature, and the ambient temperature further impacts the OCXO board.  As temperature increases (due to either increased current or increased ambient temperature) the counter shows the frequency increases, as temperature decreases the counter shows the frequency decreases.  And of course there are time lags everywhere, especially with temperature changes but also with current changes.  No doubt the current and temperature changes are impacting resistance which together with the voltage impacts the current.  It is a lot of around and around and back and forth.

EDIT:  a challenge with the temperature measurement is that while the sensor sits close to (is touching) the OCXO board it is hard to know if the temperature is due to changes in the current drawn by the board (which is limited by how much current the PS makes available), or if the temperature is due to changes in the ambient temperature (if the Air Conditioning is on cooling occurs, if the AC if off heating occurs).  Likely the sensor is showing some cumulative effect of the current and ambient temperature.

[Andrew_Debbie]

I'm going to let it run for a few days.

48 hours later. . .

My counter is reading 10.00000001 MHz.    That is .03Hz lower than on Monday.    I don't know what the spec. is for the OC5SC25.    Perhaps the observed drift is due to variations on the adjust pin. 

A real LT1009 from Analog/LT is spec'd 20ppm/kHr @ 25C  typical.  There is no min or max.   Thermal drift over the temperature range in my office is perhaps a few mV.



It shouldn't be hard to swap in an LT1019A which is 3ppm/℃ typical.    One from Digikey would cost more than I paid for the entire board.   Maybe worth it for boards that came with "bad" LT1009 clones?

 
I'm using the internal Option 04A Ovened Oscillator as a reference.      The spec is 3x10^-9/day after 3 months continous operation.   My over the weekend check with the LBE-1420 found it to drift less than 1x10^-9/day.   When possible I will check the internal timebase drift over several weeks.  weeks.  I might / should change the 35 year-old power supply capacitors first.

I can't use my GPSDO on my desk.  Not yet.  I'm looking into a way to get the antenna a good view of the sky.

[rhb]

It’s hard to say which I find more amazing, the performance or seeing them for $13 as a complete module.

Reading people’s recent comments I find the claims by some that they are junk laughable.  I wish I could find more such “junk”.

Have Fun!
Reg

[Electro Fan]

It’s hard to say which I find more amazing, the performance or seeing them for $13 as a complete module.

Reading people’s recent comments I find the claims by some that they are junk laughable.  I wish I could find more such “junk”.

Have Fun!
Reg

+1

I have tried several of these and while they vary, if you get a good one it can be impressive for the price.  This is from a $13 unit with no adjustments to the trimpot.

[Electro Fan]

fwiw, the Min-Max variation might be somewhat due to the temperature variation.  The sensor is sitting near/touching the OCXO module but it is no doubt measuring not only the module temp but also the ambient temperature which fluctuates with the air conditioning going on and off.  I'm guessing the temperature variation is also due to some power supply current fluctuation.  Point is that for not much $ it's possible to get pretty good accuracy and stability even without much if any attention given to packaging.

(One of the GPSDO's is providing a 10 MHz ref to the counter.)

[GigaJoe]

in average, the oscillator minimizing drift after 2-3 weeks.   

[rhb]

Since when is  0.37 ppb “pretty good”?  Stick it in a box with some polyester batting and I expect it will do near the 0.1 ppb of my first two.  I have checked them a few times since and they stabilize to the measurement limits of my 5386A referenced to one of Leo’s dual channel GPSDOs within 20 - 30 minutes.  It’s quite a bit better than the OXCO in my 5386A.

Of the next 3, one had a cap busted off in shipping and the other two wouldn’t adjust to 10 MHz.  Stability was good, just the correct tuning voltage was out of range of the trimmer. I’ll fix that eventually.

I have 10x too many projects which means only a few get completed. But I have fun and that’s all I care about at 71.  Life is getting short. After learning I would need to drive 75 miles 5 days a week for 8 weeks to get radiation treatment for a recurrence of prostate cancer, I ordered a Toyota GR86.  If I’m going to drive that much I decided I should finally buy a proper sports car.  The 2nd new vehicle in my life.  I still have the first, a 1993 base model Toyota pickup.

Have Fun!
Reg

[Andrew_Debbie]

It’s hard to say which I find more amazing, the performance or seeing them for $13 as a complete module.

Reading people’s recent comments I find the claims by some that they are junk laughable.  I wish I could find more such “junk”.

Have Fun!
Reg

The OSC101 variant I have isn't nearly as good as the sz-plaza rev 0.2 module.     

The OSC101 powers the adjust pin from a generic 78M05.     It drifts with input voltage.   It drifts with ambient temperature.     Connected to an HP linear bench power supply, observed drift in one hour is about 400x  the sz-plaza drift per day.

[Electro Fan]

Since when is  0.37 ppb “pretty good”?  Stick it in a box with some polyester batting and I expect it will do near the 0.1 ppb of my first two.  I have checked them a few times since and they stabilize to the measurement limits of my 5386A referenced to one of Leo’s dual channel GPSDOs within 20 - 30 minutes.  It’s quite a bit better than the OXCO in my 5386A.

Of the next 3, one had a cap busted off in shipping and the other two wouldn’t adjust to 10 MHz.  Stability was good, just the correct tuning voltage was out of range of the trimmer. I’ll fix that eventually.

I have 10x too many projects which means only a few get completed. But I have fun and that’s all I care about at 71.  Life is getting short. After learning I would need to drive 75 miles 5 days a week for 8 weeks to get radiation treatment for a recurrence of prostate cancer, I ordered a Toyota GR86.  If I’m going to drive that much I decided I should finally buy a proper sports car.  The 2nd new vehicle in my life.  I still have the first, a 1993 base model Toyota pickup.

Have Fun!
Reg

Reg, Thanks for all the insightful info in your posts.  Hope you are enjoying the GR86 and most importantly that the treatments are going as well as possible.  EF

[Electro Fan]

When stuck in the rabbit hole, keep measuring

Here is the most recent addition to the $13 OCXO module collection.  Unlike the others I tested the trimpot behaves in a consistently predicable manner.  (The trimpots on the other units barely seemed connected to their circuit - adjustments made very little impact and sometimes the impact was unpredictable.)  With this unit I was able to dial in something close to 10 MHz.  According to my GPS disciplined counter it is reasonably accurate and stable even though it is not shielded in any way.  I have some cases so next I'm going to see if I can protect the OCXO module from the ambient temperature swings.  But even without any improvement my main conclusion is that any piece of test equipment over several hundred $ should have at least comparable performance, or a 10 MHz ref in.