Author Topic: Low cost <1 ppb 10 MHz OXCOs on ebay  (Read 20094 times)

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Offline rhbTopic starter

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Low cost <1 ppb 10 MHz OXCOs on ebay
« on: April 15, 2023, 08:24:09 pm »
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
 

Offline james_s

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #1 on: April 15, 2023, 08:37:10 pm »
I see the boards, but I don't see any bare oscillators. I wonder what these came from? Cell sites?
 
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Offline I wanted a rude username

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #2 on: April 15, 2023, 08:41:53 pm »


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.
 

Offline SCSKITS

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #3 on: April 15, 2023, 11:31:03 pm »
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
SCS, DIY upgrades for older test equipment
 

Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #4 on: April 16, 2023, 01:14:19 am »
 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

 

Offline ch_scr

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #5 on: April 16, 2023, 06:57:27 am »
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.
 

Offline 807

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #6 on: April 16, 2023, 11:06:24 am »
@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
 

Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #7 on: April 16, 2023, 05:29:35 pm »
@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
 

Online MIS42N

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #8 on: April 18, 2023, 10:09:58 am »
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.

 
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Offline james_s

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #9 on: April 18, 2023, 07:58:57 pm »
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.
 
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Offline Datman

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #10 on: May 02, 2023, 02:52:02 pm »
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.
 

Offline GigaJoe

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #11 on: May 03, 2023, 05:03:05 am »
"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.
« Last Edit: May 03, 2023, 05:20:40 am by GigaJoe »
 
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Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #12 on: May 04, 2023, 06:15:36 am »
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.
 

Offline Datman

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #13 on: May 05, 2023, 07:29:51 am »
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.
 

Offline 807

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #14 on: May 05, 2023, 10:52:00 am »
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.
 

Offline Datman

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #15 on: May 05, 2023, 12:09:45 pm »
0 to 4V -> -2 to +2 ppm:
 

Online MIS42N

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #16 on: May 05, 2023, 01:14:48 pm »
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.

 

Offline james_s

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #17 on: May 05, 2023, 07:47:21 pm »
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.
 
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Online MIS42N

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #18 on: May 05, 2023, 10:26:53 pm »
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.
 

Offline GigaJoe

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #19 on: May 06, 2023, 04:59:32 am »
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

 

Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #20 on: May 08, 2023, 04:50:57 pm »

[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
 

Offline Yrrah

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #21 on: May 08, 2023, 07:45:35 pm »
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?
 
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Offline Yrrah

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #22 on: July 25, 2023, 01:19:28 pm »
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.
 
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Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #23 on: July 25, 2023, 09:05:46 pm »
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
 

Offline Yrrah

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #24 on: July 28, 2023, 08:10:38 am »
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
 

Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #25 on: July 28, 2023, 12:48:45 pm »
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
 

Online WatchfulEye

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #26 on: July 30, 2023, 06:09:03 pm »
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.



 
 
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Online MIS42N

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #27 on: July 30, 2023, 10:53:50 pm »
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.
 
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Offline Yrrah

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #28 on: August 16, 2023, 06:57:10 pm »
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
 

Online WatchfulEye

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #29 on: August 20, 2023, 01:23:31 pm »
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.
 
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Offline rhbTopic starter

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #30 on: August 21, 2023, 03:18:06 pm »
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.
« Last Edit: August 21, 2023, 05:36:21 pm by rhb »
 

Offline tszaboo

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #31 on: September 13, 2023, 08:36:58 pm »
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?
 

Offline alligatorblues

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #32 on: September 13, 2023, 10:20:43 pm »

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.
 

Offline 807

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #33 on: September 14, 2023, 10:51:39 am »
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
 

Offline Kean

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #34 on: September 14, 2023, 01:22:57 pm »
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.  :-+
 

Offline tszaboo

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #35 on: September 14, 2023, 03:09:38 pm »
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.
 

Offline Kean

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #36 on: September 14, 2023, 03:13:32 pm »
Yeah, see that GPSDO forum topic I linked to
And https://github.com/ajcashin/budget-gpsdo
 
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Online MIS42N

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #37 on: September 16, 2023, 11:18:14 am »
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).
 
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Offline vindoline

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #38 on: September 17, 2023, 02:22:35 am »
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.
 

Offline Andrew_Debbie

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #39 on: May 23, 2024, 02:47:38 pm »

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.




« Last Edit: May 23, 2024, 02:50:08 pm by Andrew_Debbie »
 
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Offline David Hess

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #40 on: May 23, 2024, 08:32:54 pm »
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.
 

Offline Andrew_Debbie

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #41 on: May 24, 2024, 02:52:58 pm »
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. 


« Last Edit: May 24, 2024, 02:55:28 pm by Andrew_Debbie »
 

Offline ZhuraYuk

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #42 on: May 29, 2024, 03:01:58 pm »
Bought 5 pieces OSC5A2B02  at aliexpress,  https://www.aliexpress.com/item/1005006457029106.html.
Three had horrible jitter, were not usable. Avoid buying these.
2257690-0
2257714-1
« Last Edit: May 29, 2024, 03:05:43 pm by ZhuraYuk »
 
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Offline Andrew_Debbie

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #43 on: May 30, 2024, 01:01:27 pm »
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.   



« Last Edit: May 30, 2024, 05:48:03 pm by Andrew_Debbie »
 

Offline 807

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #44 on: May 30, 2024, 10:29:57 pm »
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/
 

Offline floobydust

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #45 on: May 31, 2024, 12:02:13 am »
807, they now ship sz-plaza boards (REV:0.0.2) with a 200kΩ (204) trimpot which gives a VCTRL 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.
 

Offline 807

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Re: Low cost <1 ppb 10 MHz OXCOs on ebay
« Reply #46 on: June 01, 2024, 12:31:51 pm »
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?
 

Offline KedasProbe

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Re: Low cost <1 ppb 10 MHz OCXOs on ebay
« Reply #47 on: June 16, 2024, 04:17:17 pm »
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.
« Last Edit: June 16, 2024, 04:40:19 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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