Cheap chinese 10 MHz OCXO Frequency Reference Modules - Page 1
Forum section: electronics / projects

author: Transradio
author_rank: Newbie
timestamp: February 16, 2023, 01:55:04 pm
content: On various e-commerce platforms chinese 10 MHz Frequency Reference Modules with OCXO have recently been offered at a favorable price. These are mostly equipped with used oscillators that have been removed from decommissioned GSM/UMTS base stations. These surplus OCXO are in in most cases OSC5A2BO from chinese manufacturer CTI (a data sheet of a comparable OXCO from CTI is attached). These Voltage Controlled OCXO have an input for a tuning voltage with a span of 0 to 4V. With the help of this tuning voltage the Quartz Crystal can be adjusted by a few Hertz to the exact target frequency to compensate manufacturing scatter or the effects of aging.I ordered one of those black modules, branded as "sz-plaza.com Rev:0.0.2". Frequency adjustment is done by a 25 turn Cermet potentiometer. Unfortunetaly the OXCO could not be adjusted to 10MHz. The adjustment range of the tuning voltage was not enough to get the thing on frequency. To find a possible fix i reverse engineered the module.It turned out to be simple to extend the limited range of the tuning voltage. It needs just a shortcut of one resistor and removing of another resistor. Please check: only the inner connector of the SMA Connectors of my module were properly soldered to the PCB, the ground connector needed resoldering. Despite the typical chines quality issues, IMHO this modules are a good bargain, a new OCXO with the same performance would cost a lot more.The modules schematics with the proposed modifications is attached. The reverse engineering was done by best efforts, there is no guarantee for correctness.

author: CaptDon
author_rank: Super Contributor
timestamp: February 16, 2023, 02:59:54 pm
content: So it seems like it was 'returned from the field' as defective and resold as tested/working and yet could not be adjusted to the stated frequency. I guess if you paid over $10 with no assurance the unit could meet original specs you paid to much?

author: Transradio
author_rank: Newbie
timestamp: February 16, 2023, 03:10:46 pm
content: The OCXO is of high quality and works perfect, the module around the OCXO has deficiencies with regards to the voltage range of the tuning voltage. You need to know that in China and elsewhere many thousands of GSM/UMTS Basestations are going to be replaced by new 5G Stuff. The OCXO are taken out of those. Good example for recycling of electronic goods.

author: 807
author_rank: Frequent Contributor
timestamp: February 16, 2023, 03:23:33 pm
content: I'm waiting for one of these to arrive.What did you use to measure the 10MHz? How far off frequency was it before the mod?

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 16, 2023, 03:44:57 pm
content: For a 10MHz reference, you could buy a cheap GPS stabilized source. You don't need to adjust it for the drift, unless they shutdown the civilian GPS signals.

author: strawberry
author_rank: Super Contributor
timestamp: February 16, 2023, 04:26:08 pm
content: Quote from: 807 on February 16, 2023, 03:23:33 pmtwo channel oscilloscope and 10MHz referenceboth waveform wont drift if frequency is equal

author: 807
author_rank: Frequent Contributor
timestamp: February 16, 2023, 05:48:39 pm
content: Quote from: strawberry on February 16, 2023, 04:26:08 pmYep. That's how I used to do it.Then I got a Racal Dana 1991 frequency counter with an external 10MHz reference from a Leo Bodnar GPSDO. Can read down to 1mHz using that combo.

author: Transradio
author_rank: Newbie
timestamp: February 16, 2023, 06:28:12 pm
content: QuoteI used a tinyPFA against a good 10 MHz GPSDOCXO as Reference. A great tool:https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.HomepageQuoteTo to adjust to the target frequency of exactly 10 MHz a tuning voltage of 1.4V is required for my specific OCXO. The adjustment range of the Module's Potentiometer without Modification reaches only from 0V to 0,8V. So i was approximately 2Hz off. Because of aging, the tuning voltage to reach 10 MHz is a bit different for each OCXO specimen.For information:the control voltage range of a new CTI OCXO ist 2V ± 2V ( 0...4V)that voltage range corresponds to a total frequency variation of approximately ±10Hz max.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: February 20, 2023, 05:37:45 pm
content: had some play with ocxo itself, not the board, as it doesn't make sense to buy it.this is AC type of quartz cut, technically more deviation from manufacturer due to larger residue stress.i use lt1021 in plastic as voltage source for compensation, thermally glued to ocxo case, and isolate everything by heavy styrofoam insulation boxable to adjust to -11 precision, drift per year approx: -5-10 degree, quite sufficient as reference for most stuff.one ocxo die in a few month - the heater went off.

author: 807
author_rank: Frequent Contributor
timestamp: February 21, 2023, 11:59:01 am
content: I bought the same module as the OP, as it was the quickest way to obtain one in UK. There's 1 UK seller on ebay for just under £19. Could have got the OCXO itself cheaper from China, but then I don't want to wait.I want to use it to replace the internal 10MHz on my frequency counter, using it's 5v supply. I'll see what voltage I need to trim it to frequency before deciding on which precision voltage reference to use. Need to replace the LT1009 with something tighter, 5ppm or less.

author: Detlev
author_rank: Regular Contributor
timestamp: February 27, 2023, 07:10:12 pm
content: I had also ordered two such OCXO. Yesterday I had one matched the OCXO to the frequency counter (synced to a Leo Bodnar GPSDO).Today I ran a measurement over 5 hours (18000 measurements with a gate time of 1s). Before that I let the OCXO warm up for 3 hours. The oscillator was on the workbench and the average temperature was 20 degrees Celsius.In those 5 hours it has a P-P deviation of 16.09 mHz. The absolute deviation was 21.68mHz. For a 20€ OCXO I think that's OK. Now it comes in a nice case and gets an output driver.Best regardsDetlev

author: 807
author_rank: Frequent Contributor
timestamp: February 28, 2023, 05:16:31 pm
content: Been playing with my module past couple of days. Like you Transradio, I couldn't get it to trim to exactly 10MHz. As it came, it settled down very quickly to 10.00000313MHz (+3.13Hz high). The range of the preset set the frequency to +1.80Hz to +3.49Hz. Looking at the Vref pin on the OCXO, this corresponded to a range of 1.940v to 2.1085v. I was puzzled as to why the voltage didn't drop to 0v when the preset was fully CW as, according to your schematic, it should have grounded the Vref voltage. It turns out that the tuning arrangement on my module is different to yours. Rather than needing an increase in Vref voltage, I need to decrease mine.I've attached the schematic of my module. I was unsure about R2 & R6, as I thought they were marked 688, which is 6.8GOhms! Then I realised that the marking was actually 68B, which is the EIA-96 code for 4.99kOhms.Within 5 minutes of switch on, it was within 180mHz of it's final settled frequency (within around 30 minutes). I havent done extensive measurements, but 5 hours later it hadn't changed.

author: RCL
author_rank: Newbie
timestamp: March 01, 2023, 09:35:45 pm
content: Gentle Readers:I felt guilty just sitting on the side-lines and letting you solve my problems. So here is my contribution:1.945 volts at the V/C pin = 10,000,005.8 Hz2.114 Volts at the V/C pin = 10,000,007.4 HzThe temperature of the little TO-220 voltage regulator (12 Vdc applied). = 105° FMy calculations indicate that at 1.332 Volts we can achieve 10 MHz.

author: fourfathom
author_rank: Super Contributor
timestamp: March 18, 2023, 05:09:04 pm
content: Quote from: 807 on February 28, 2023, 05:16:31 pmI just got two of these boards. They match your posted schematic (thanks for that!), and they also needed a lower tuning voltage (about 1.89V for one of them). I ended up replacing R3 (it was 36K) with a 3.3K resistor, I didn't calculate an optimum value, I just had a 3.3K handy, but the tuning range calculates out to 0.947 to 2.125 (assuming no loading from the OCXO Vref input.) I put the OCXO output, and a Bodnar GPSDO output on the 'scope, and it looks quite stable.

author: rhb
author_rank: Super Contributor
timestamp: April 17, 2023, 05:07:38 pm
content: I'm currently playing with a pair of these with 3 more in transit and 10 bare modules. The lattr will be tested in a fixture with an LM399 voltage reference and low temperature coefficient trimmer pots in as stable a temperature oven as I can make. I've not needed to make any changes to the first 2.I'm not able to get better than +/- 0.01 Hz with it in an insulated craft beer six pack filled with fiber batting.Next step will be a simple thermistor and pot biasing the base of a 2N3904 with a 240 ohm resistor as a heating element to form a second oven inside an insulated box. The hard part will be finding the thermistors and a suitable trim pot in the chaos.I also need to load tinyPFA on a dedicated nanoVNA 4H. I'm alos using one of Leo's GPSDOs.Have Fun!Reg

author: radiolistener
author_rank: Super Contributor
timestamp: April 17, 2023, 05:12:52 pm
content: these OCXO were in use and desoldered from some equipment. There is some risk that they were stored in bad condition or improperly desoldered (with blowtorch or by frying PCB on the fire)

author: rhb
author_rank: Super Contributor
timestamp: April 17, 2023, 08:08:47 pm
content: The plane might get hit by a meteorite on the way.At this point I think I'm fighting the Vref on the board. If I trim it, it's very tight for 20-30 minutes and then it's off by the same 0.012 - 0.021 Hz. I've been through this exercise many times now. I think the Vref shifts when it reaches thermal equilibrium.I have some LM399 voltage references so I'm going to box one to use as the Vref for testing all the OXCO modules with TL082 followers to drive the trimmer circuits which will be thermally isolated from the OXCO. I'll also heat each OXCO to the point the internal heater turns off so that there are minimal heat gradients within the module itself.Reg

author: wasedadoc
author_rank: Super Contributor
timestamp: April 17, 2023, 09:19:56 pm
content: Quote from: radiolistener on April 17, 2023, 05:12:52 pmThe 5 that I have were still soldered to their PCBs. The PCBs had been cut a few millimetres from the edges of the OCXO can. Cuts were clean. No sign that they were crudely done with a large scissor-like tool.

author: 807
author_rank: Frequent Contributor
timestamp: April 18, 2023, 08:59:18 pm
content: Quote from: wasedadoc on April 17, 2023, 09:19:56 pmI have 2 like that, the other 4 I bought were desoldered. Need to get an idea of the Vref for each of them before deciding which reference voltage chips to buy.

author: rhb
author_rank: Super Contributor
timestamp: April 20, 2023, 02:25:42 am
content: Buy a good quality reference and use a TL082 and temperature stabilized foil trimmer and similar grade fixed resistor to trim the value for Vctl. Then put that in a thermally controlled enclosure.

author: artag
author_rank: Super Contributor
timestamp: April 22, 2023, 02:15:08 pm
content: I bought one mounted on a board (black solder resist, schematic approximately as 807's) and 5 unmounted (desoldered). I found I couldn't adjust the frequency at all (it settles to about 4Hz high in less than 2 minutes, vs a GPSDO). This seems to be because the adjustment pot - which is 200K in this example - doesn't seem to have the centre pin connected to the end, so it functions as a fixed 200k resistor,Linking 2 pins of the pot (the two nearest the adjustment screw : the pin near the edge of the board is ground, though I guess that would work too) got me down to a +2Hz error with the pot at 0 ohms so a resistor change was necessary. 18k in parallel with R3 got it in range though it's at the low resistance (somewhat sensitive) end of the travel.After adjustment to 0.08 Hz high it's drifted up to .15 Hz high in 2 days but is pretty solid there. It's in a small cardboard box full of polystyrene peanuts to let the voltage reference stabilise, heated by the oven and the linear regulator, which is supplied with 10V. However a couple of days to stabilise isn't much use for a portable instrument. This may just be settling out in the environment and after some time powered off (and probably abused mechanically). I'll have to see what it now achieves from cold.After some thermal cycles and resets but no adjustment the frequency had increased to 10M + 0.19. However it's stuck there (about 5x10^-10 variation) ever since, despite another 12 hour cool/heat cycle, a brief interruption and 2-3 days on test. After cooling the oscillator is stable in a couple of minutes but the entire board and enclosure has to warm up before the voltage source is at temperature.Very grateful for the schematic. Opaque solder resist is a crime.Interested to see what people come up with for an improved pcb and reference.

author: 807
author_rank: Frequent Contributor
timestamp: April 23, 2023, 11:47:07 am
content: Did they base this circuit on just 1 sample of the crystal & thought the rest would be the same? Seems like they didn't allow enough adjustment to cover the spread of Vref.I calculate that I need somewhere around 1.76v for 10MHz. Halving the values of R1 & R3 should give a range of 1.63v to 1.92v. Haven't got round to doing it yet. Those resistors are very small. Might need a digital microscope for my ageing eyes.

author: rhb
author_rank: Super Contributor
timestamp: April 26, 2023, 02:17:35 pm
content: The temp co on Vishay's *best* foil trimmer is 5 ppm/C. That will require temperature compensation of its own to get them to <0.01 ppb and a good LM399 reference.The last 3 finished boards are all several Hz high. Haven't checked on the 10 bare module shipping lately, but hopefully they will arrive soon and I can start working out how to thermally stabilize these more tightly.Reg

author: MathWizard
author_rank: Super Contributor
timestamp: April 27, 2023, 09:53:13 pm
content: How good/bad are the reference oscillators/clocks, that are found on common computer hardware PCB's, or say like a digital cable TV box ?

author: Gyro
author_rank: Super Contributor
timestamp: April 27, 2023, 10:03:05 pm
content: Once upon a time, digital TV boxes had reasonably decent 27MHz VCXOs, then the market cheapened, and skip and repeat became the standard way of maintaining broadcast synchronisation.

author: fourfathom
author_rank: Super Contributor
timestamp: April 28, 2023, 05:44:38 am
content: Quote from: MathWizard on April 27, 2023, 09:53:13 pmComputer hardware often has xtal oscillators with on the order of 20 ppm accuracy (initial plus over temperature and ageing). Gear that needs better might use a 5 ppm oscillator. Otherwise you are in OCXO or GPSDO territory, and no generic computer hardware requires that. There are of course exceptions.

author: rhb
author_rank: Super Contributor
timestamp: April 29, 2023, 01:03:59 am
content: Some stray thoughts on the topic:A well designed OXCO reference should have a 10 MHz reference input and circuitry to synchronize the OXCO automatically. Include a 10 MHz xtal filter TRF receiver as a backup phase reference.The Vref thermals are my biggest concern. A block of aluminum with active temperature control via Peltier junction may be essential to setting the Vref for the OXCOs.If you track the OXCOs for a few months to model their frequency drift over time, one could then reset all of them by finding the optimal L0 solution for the voltage shifts to make them all agree. How many references do you need to prevent divergence?The other big concern is the internal OXCO heaters. Those cause thermal gradients, so the units should be independently set to the required temperature to prevent that turning on.Reg

author: tmiller
author_rank: Contributor
timestamp: April 29, 2023, 06:57:01 pm
content: I put one of these OCXOs in an insulated foam block and measured the outside temperature of 50 C. Has anyone dissected one of these units? They look to be laser welded.

author: jimmc
author_rank: Frequent Contributor
timestamp: April 29, 2023, 07:39:59 pm
content: A few more data points for the bare oscillators, these were purchased 2 years ago on 'butchered' boards.Interesting variation in control voltage current between units.Jim

author: rhb
author_rank: Super Contributor
timestamp: April 29, 2023, 09:23:11 pm
content: Thanks. Would you post the details of your test set up? Your results suggest I'll need to test them before I build the fixture to test them.I think the discrepancies in tuning voltages are simply aging effects over many years moving the thresholds in varying directions.The most pressing question in my view is what's the dF/dV when the units are warm enough to not run their internal heaters. How tight does the voltage need to be to hold 0.1 ppb?Reg

author: 807
author_rank: Frequent Contributor
timestamp: April 29, 2023, 10:56:25 pm
content: Quote from: tmiller on April 29, 2023, 06:57:01 pmIMSAI Guy on youtube takes the lid off one of these in this video (from 1:45)...

author: tmiller
author_rank: Contributor
timestamp: April 30, 2023, 01:02:51 am
content: Note that there is no thermal insulation in the can except dead air.

author: rhb
author_rank: Super Contributor
timestamp: April 30, 2023, 01:32:47 am
content: Very good video. Thanks!Short term stability is given as 0.02 ppb/s and long term (>10 years) 0.4 ppb/yr.If you measure the frequency under stable conditions a dozen or so times over the course of a year, you'll be able to eliminate the aging error for a year. Your prediction will be "good enough (1-2% of the annual aging rate)" for as long in the future as you have data from the past.By carefully isolating them and externally heating them I think 0.1 ppb or better long term is doable.with periodic cals at ever longer intervals.I have a EMI enclosure I built. It still needs the Peltier junctions, insulation and thrus installed, but it will let me examine whether the 0.02 ppb/s is intrinsic or EMI.Suppose you combine 3 of these with provision to periodically attach a GPSDO, measure, correct and recalculate the aging rate. That leaves temperature and reference voltage control. Those pretty much go hand in hand already. Use an MSP430 to adjust voltages and temperatures as needed using latching DACs. Whenever the unit is started up, it calculates how many hours it's been operating, applies the appropriate control voltages and notifies the user when the frequency is stable. Realistically that's an hour or less.Cheap "well aged" LM399s and OXCOs are quite marvelous if the price allows junking the less than perfect ones or merely using them in less demanding roles.Reg

author: jimmc
author_rank: Frequent Contributor
timestamp: April 30, 2023, 04:27:49 pm
content: Quote from: rhb on April 29, 2023, 09:23:11 pmTest set up was nothing special, test clips were connected to the power and control pins, a Kelvin clip attached to the ground pin to to keep the main supply and control voltage grounds separate and a x10 'scope probe connected to the output pin.Al supplies, meters, counter and GPSDO were floating, only the 'scope used for phase comparison was connected to mains earth.I agree that the unit to unit variation in control voltage required for 10MHz is to be expected.My interest was in the current sunk (or sourced) by this pin.All of the units tested were well in spec. (Rin>100k), but the three lowest serial numbers are all similar and sink no current whereas the other two sink significant (and similar) currents.I wonder if this is a design change or is just coincidence.Jim

author: rhb
author_rank: Super Contributor
timestamp: May 01, 2023, 07:02:08 pm
content: Thanks. I'll plan on hooking them all up to power with dividers for each unit Vref and run them for an hour or two before making detailed measurements.I'll set up a fixture for 3 OXCOs and feed those and the GPSDO to a 4 channel scope. If things look promising I can measure periods on 8 channels with an 11801 and 4 dual channel SD-26s by triggering on the GPSDO using a delay line. The theoretical resolution is 10 femptoseconds. Though 100-200 fs is really the limit because of noise.Have Fun!Reg

author: comsec22
author_rank: Contributor
timestamp: May 21, 2023, 02:56:38 pm
content: Detlev, what instrument has been use for the picture below Your post ?Danke

author: Detlev
author_rank: Regular Contributor
timestamp: May 21, 2023, 05:08:11 pm
content: Quote from: comsec22 on May 21, 2023, 02:56:38 pmthis is the Tektronix FCA3000, identical in construction to the Pendulum CNT-90. What I don't like is that FCA doesn't have a web interface

author: mojoe
author_rank: Frequent Contributor
timestamp: February 16, 2024, 07:26:45 am
content: I didn't know about this thread when I recently purchased two of these OCXO modules. A kind member sent me a link.My modules are similar to the second schematic that was posted, with some different resistor values, and the trimpot is 200 K. One of my modules needed a resistor change, the other was good as-is.I'm using my HP counter, so that I can log data. The counter reference is my HP GPSDO. I set a 10 s gate time to get 11 digits (0.000 Hz). The modules are sitting on the bench, in the open air. The room temperature runs 70-76 F. So far, just watching over several minutes, the frequency stability is impressive, just a few mHz.Now that I have the first module at exactly 10 MHz, I'm logging data for the next 24 hours to see how it drifts. I'll log the second module later.At some point, I need to flash my NanoVNA H4 with the PFA firmware.For $18 each, I think these are a very good deal. Once in an enclosure, the stability should be a bit better, due to minimized temperature variations.I also ordered two of those UCT (Oscilloquartz) OCXO's being sold on ebay as "new". They are supposed to be double oven. It will be interesting to compare them with these CTI OCXO's. I ordered the UCT's to use in a DIY GPSDO.

author: rhb
author_rank: Super Contributor
timestamp: February 16, 2024, 12:52:16 pm
content: Send the OXCO & GPSDO signals to a scope triggered on the GPSDO. Use splitters if you have them available with a 50 ohm thru at the scope. Or a tee to the scope without a terminator. That will show you what the counter can't.Looking forward to your device comparison.Have Fun!Reg

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 16, 2024, 02:01:48 pm
content: “At some point, I need to flash my NanoVNA H4 with the PFA firmware”I have both a NanoVNA H4, and a TinyPFA. They are excellent and interchangeable with a firmware load.Use TimeLab to plot the frequency difference, it is surprising how much even an “ultra high stability” oven oscillator drifts… and how near impossible it is to put one on frequency to better than around 2 parts in 10^10. This was the 10 MHz output of my Racal counter which has the 04E oven option.

author: mojoe
author_rank: Frequent Contributor
timestamp: February 16, 2024, 03:21:10 pm
content: Quote from: rhb on February 16, 2024, 12:52:16 pmI already did the scope comparison. It didn't really get me anything better. At only a few mHz difference, the second trace was almost stationary. I guess if I waited minutes, I would have had some appreciable movement.

author: mojoe
author_rank: Frequent Contributor
timestamp: February 17, 2024, 10:20:53 am
content: I have some results, but I probably need to let the OCXO settle longer after adjustment, before I measure things. Over the entire 24 hours, there was a total difference of 24 mHz, but during the last half of that time, it was only a spread of 10 mHz. I'll let this cook for a while longer and repeat the experiment.Still, for sitting in the open air, the results are pretty decent. When I measure it again, I'll probably put it in a box.This is the same OCXO that is in the 2020 version of the BG7TBL GPSDO.

author: rhb
author_rank: Super Contributor
timestamp: February 17, 2024, 01:47:33 pm
content: Add some cotton or polyester batting when you box them. Not too much.I was timing half period times of 1-2 minutes on the scope when I was setting mine.I came to the conclusion that setting the exactly needed an MCU.Have Fun!Reg

author: mojoe
author_rank: Frequent Contributor
timestamp: February 21, 2024, 08:23:41 pm
content: Another 24 hour run. This time, I let the OCXO settle for several hours after my last adjustment. As before, room temperature from 70-76 F. I still haven't put it in a box.I had it set to exactly 10 MHz (at least for a while). The drift was much better than before. It went from only 1 mHz low to 8 mhz high, mostly staying close to 10 MHz. I'm impressed. I'm going to put a fork in it and call it done, except for finding a suitable box.Later, I'll probably see how long it takes to come back on frequency after sitting cold for a while.

author: cncjerry
author_rank: Unknown
timestamp: February 22, 2024, 02:08:56 am
content: The phase noise I measured on this "CTI" module would prevent me from using it just about anywhere. You can find a much more stable oscillator on ebay like a wenzel for not much more money that has 10 to 15dB or better phase noise performance. The biggest problem is the shared power supply that drew as much as 750ma while heating. You can still find Hp 10811s that have a split heater and crystal supply that are better. The thing that makes this module interesting is the packaging but there are PCBs that take wenzel and morion oscillators.Jerry

author: rhb
author_rank: Super Contributor
timestamp: February 22, 2024, 03:03:38 pm
content: Quote from: cncjerry on February 22, 2024, 02:08:56 amWhere are your measurements?Reg

author: cncjerry
author_rank: Unknown
timestamp: February 23, 2024, 06:01:53 am
content: I had started a thread after purchasing one and comparing it to other oscillators in roughly the same price range. I've never seen an oscillator draw such a perfect frown from it's phase shift given the room it was in was +/- 2 degrees of 72 while I ran the test. Phase noise attached.I don't know if these are CTI oscillators. I have other CTI oscillators and yes, they could be using a laser to etch them now, but the older ones I have had a different marking. For $20 more, sometimes less, you can get a Wenzel sprinter (500 or 501 series), that's maybe 4x the size (yes, that could be a factor), has much better PN and stability and uses half the power while warming up. The lower (lighter) line on the chart was the noise floor for that test. I was running the oscillator behind a stacked LT3045 regulated supply. There was a spur sticking up above the PN at 300hz. This is only one sample. But at -145, I wouldn't want this one in a radio. They advertise them as audio ADC clock replacements. That might be OK if you had one that took 10Mhz.

author: mojoe
author_rank: Frequent Contributor
timestamp: February 23, 2024, 07:56:54 pm
content: Your graph shows that it meets or almost meets the specifications. In the middle, it is just a bit worse. I don't have the ability to measure phase noise, but I've seen others post measurements of these OCXO's, and they show numbers better than spec. Considering that these are used and abused, and you've only tested one sample, I don't think that you can call them terrible.I agree that I wouldn't used them for most RF purposes. But that's not how they're spec'ed. Yes, there are OCXO's with better phase noise. In fact, I am awaiting some from ebay.

author: switchabl
author_rank: Frequent Contributor
timestamp: February 23, 2024, 10:51:45 pm
content: It looks ok to me for a low cost OCXO. Most new ones won't be significantly better unless they are explicitly specified for low phase noise ($$). I wouldn't get the PCB module, the designer either didn't know what they were doing or they didn't care. But the bare oscillators are pretty good value at 3$ (!) each.I'm pretty sure they are not fake. They are clearly salvaged, some of them are still soldered to (a piece of) the original PCB. I agree they are most likely from previous generation cellular base stations. And almost certainly a custom part with specs that are just good enough for that application.Yes, you can get (a lot) better; for >10x the price. No, you probably shouldn't derive the LO of your X-band transceiver from it. Still, if you just want to replace the oscillator in your frequency counter with something reasonably stable or want to build a budget GPSDO, it is totally fine. For a lot of ham projects as well.

author: cncjerry
author_rank: Unknown
timestamp: February 24, 2024, 07:02:16 am
content: It's hard to tell from a picture, but look at this one:https://www.ebay.com/itm/144769640308That looks like a read CTI impression. The one I received looks more jagged, like the anti-aliasing wasn't turned on.Granted they have gone up in price lately, but you can still find Wenzel 10Mhz (and other frequencies) in the 500 or 501 series, for under $50. I bought quite a few over the last few years and don't think I paid more than $45 for any of them. There were some 5Mhz versions around that had exceptionally good performance, really low PN and very stable. If you take a small solder protoboard, mount the Wenzel 500 series as they just fit, put a few bigs caps on the other side of the board and a few bypass, throw a on a regulator and if you are serious, a voltage reference and a 10turn pot you will have a decent reference for your counter that can also drive your SDR, etc. Depending on the 500 series you get, they generally are -163 or -173 at 2k. The Wenzel 500 series have a screw cap on a trimmer capacitor and you can generally get them really close. I have a pair of very low PN 26Mhz for my phase noise test setup.I plotted a frequency deviation chart on the thread I started. I can't figure out what caused the oscillator/board to do that arc. I'm going to put a thermometer on it and plot that and the current and rerun the test.Jerry

author: mojoe
author_rank: Frequent Contributor
timestamp: February 25, 2024, 12:22:50 am
content: It's habit forming. I bought two more OCXO boards. This time, designed by BG7TBL, but with the same CTI OCXO's. These boards are 5 V input. There is some circuitry on the bottom of the board. I'll have to trace it out. There is some nice filtering on the 5 V input, and what I assume is a voltage reference. On the output is the same LPF as on his GPSDO's. I'll post more when I've traced out the circuit and taken some measurements.The other boards that we've been posting about have settled down nicely to just a few mHz drift (I bought two of those, also). I did a test with one, where I powered it down, let it sit for hours at room temperature, then logged the frequency when I powered it up (1 s gate time). Here is the first 30 seconds:9:37:17 PM +8.46830085E+69:37:18 PM +9.99972502E+69:37:19 PM +9.99972567E+69:37:20 PM +9.99972580E+69:37:21 PM +9.99972704E+69:37:22 PM +9.99972869E+69:37:23 PM +9.99973077E+69:37:24 PM +9.99973325E+69:37:25 PM +9.99973602E+69:37:26 PM +9.99973915E+69:37:27 PM +9.99974254E+69:37:28 PM +9.99974625E+69:37:29 PM +9.99975016E+69:37:30 PM +9.99975430E+69:37:31 PM +9.99975858E+69:37:32 PM +9.99976309E+69:37:33 PM +9.99976774E+69:37:34 PM +9.999769840+69:37:35 PM +9.99977252E+69:37:36 PM +9.99977738E+69:37:37 PM +9.99978236E+69:37:38 PM +9.99978745E+69:37:39 PM +9.99979255E+69:37:40 PM +9.99979776E+69:37:41 PM +9.99980294E+69:37:42 PM +9.99980817E+69:37:43 PM +9.99981344E+69:37:44 PM +9.99981869E+69:37:45 PM +9.99982390E+69:37:46 PM +9.99982910E+69:37:47 PM +9.99983434E+6In about four minutes, it was within 10 mHz and getting better. Another minute, and only 2 mHz off.

author: mojoe
author_rank: Frequent Contributor
timestamp: February 25, 2024, 03:20:55 am
content: On the BG7TBL boards - It looks like someone did a nice job with the circuit. There is a Pi filter on the 5 V input, and lots of bypass caps all around. U3 is a CD431 adjustable voltage reference. I measured the output of U3 at 3.76 V. With the trim pot adjusted close to 10 MHz, I measured 1.86 V to the Vref pin on the OXCO.Unlike the other boards, both of these have plenty of adjustment range on the trim pot. I'm letting them cook for a while before I try to tweak the frequency any more.

author: mianos
author_rank: Regular Contributor
timestamp: April 04, 2024, 04:47:44 am
content: I also joined the club with one of these sz-plaza rev 02 OXCOs. (My eevblog mandatory broken 3478A membership card is incoming in the mail).Mine could not be trimmed anywhere near 10Mhz.I took the reference resistor network out and injected my home brew web controlled ESP32 DAC1220 based precision voltage source and found that I needed the following voltages to tune the XCO:1.8 999,999.701.83 100,000.0002.0 100,001.603So I pulled the whole network out and designed a ladder that would give me this range with SMD components I had on hand. (I don't have a book, just a little box of about 20 of the most common values). I am sure no one is interested in a dodgy python prolog solver to work this one out..Came out OK,It's been running a few months to age it, but since the mod yesterday it's averaging about .3ppb. At the moment there is some variance so I'll probably leave it as it is.I have a LEA-M8T so when I put a better antenna up I'll try and level all this up a bit more.

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: April 10, 2024, 01:46:15 pm
content: I think these are pretty good generators, especially considering the cost. Five of them cost me less than $10. I bought just soldered-out OSC5A2B02s without the regulation board. The seller honestly states that they are used.As for the board, except for the small range of the regulation voltage, it is incorrect to load the oscillator directly to the filter to get a sine wave. It is necessary to apply some kind of buffer at the beginning.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 02, 2024, 01:14:22 pm
content: Does someone have experiences in using thermal insulation around these modules?I don't want to increase stability, that´s absolutely fine for my purpose. But I´d like to build a battery operated device and it´d be great to reduce the oven power consumption by 30-60%.

author: bostonman
author_rank: Super Contributor
timestamp: October 02, 2024, 05:42:22 pm
content: I'm curious, what are you using to measure the reference to the oscillator in question?Unfortunately I don't have access to the strip chart recorders from my old job, so I've been interested in something to measure a known good reference to a test one; within a decent budget of course.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 02, 2024, 06:38:08 pm
content: Oh I don't have the oscillator in question yet, but the plan is to compare it to a GPSDO which is always on.The general idea is to put a battery buffered OCXO into an AWG to have a portable frequency reference. I just need 0.1ppm accuracy, so a state of the art TCXO would probably do the trick too.But if it´s possible to supply the OCXO with two 18650-cells for more than a day then it´d be best. With its naked package it would come close, but I´m curious if a thermal insulation could improve the buffer time without compromising the oscillators stability or reliability too much.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 02, 2024, 07:54:14 pm
content: Quote from: Phil1977 on October 02, 2024, 06:38:08 pmIf you insulate it carefully, that will also improve a TCXO too.eg you could try this VCTCXOhttps://www.lcsc.com/product-detail/Temperature-Compensated-Crystal-Oscillators-TCXO_KDS-Daishinku-1XTV10000MDA_C253701.htmland manually trim it as it ages. 0.1ppm over a day is probably realistic, if you avoid wide temperature swings.If you are battery operating, you could also look at NTC Crystals. (crystals with a NTC inside the case on the other two pins)That can either control a miniature oven, or a correction scheme.Does it need to be 10MHz ? That's large for modern TCXO, and the NTC Crystals are usually 26.00MHz

author: rhb
author_rank: Super Contributor
timestamp: October 06, 2024, 09:38:52 pm
content: They need thermal insulation in the enclosure to suppress air currents. Further insulation provides no benefit.The heater takes a good bit of current. But if properly adjusted with a bit of fiber batting in the case they will hit 1 ppb in less than 15 minutes from cold. I have one with SMA output and one with BNC in plastic enclosures.Have Fun!Reg

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 08, 2024, 08:25:03 pm
content: Quote from: rhb on October 06, 2024, 09:38:52 pmI do not expect better accuracy as benefit. I just tested that the steady state current consumption of such an OCXO and it goes from 250mA in free air down to around 160mA in some thermally insulating foam.Usually it´s a really bad idea to thermally insulate components with significant heat dissipation, but in this case the "controlled" oven should have no problem to keep all temperatures healthy. Are there any reasons not to insulate it? I think if thermal insulation only has advantages, then the manufacturer may not have chosen a metal package.Edit: According to a chinese datasheet of the CTI OCXO the allowed working temperature range is 0°C to 75°C. The metal package in my insulating foam reaches barely 60°C. For me that sounds okay.

author: rhb
author_rank: Super Contributor
timestamp: October 09, 2024, 12:44:21 pm
content: FWIW I did multi-day trials of accuracy with the OXCO in a 6 bottle beer box full of fiber batting. However, I did not examine the power consumption. My chief concern was accuracy as I observed that the frequency shifted when I tried various orientations without the internal batting. I’m getting better than 1 ppb, which for the $25 cost including case and external connectors is stellar.I’m using external power and had not considered battery power as the instrument it would be feeding also needs power. You have made an excellent case for additional insulation. I have some more PCB modules and will probably make one up with an internal LiPo battery and the insulation as you propose.Thanks for posting about it. I didn’t see your initial post, just follow-up and did not realize your concern was power consumption. As received the power drain was so high I never considered battery power. You changed my mind about that.BTW The only serious kit of mine that doesn’t have an HPAK OXCO is my 33622A AWG.Have Fun!Reg

author: EU1
author_rank: Regular Contributor
timestamp: March 23, 2025, 09:23:17 pm
content: Quote from: 807 on February 28, 2023, 05:16:31 pmThanks a lot for reverse engineering the Rev. 0.0.2 schematic! Your work saved me a ton of time. Attached is the updated schematic for Rev. 0.0.3 in case anyone finds it useful.

author: EU1
author_rank: Regular Contributor
timestamp: March 24, 2025, 02:43:44 am
content: The Rev. 0.0.3 schematic isn’t great, to say the least. I think it should be modified as shown in the attached image. This will ensure a stable current through the shunt regulator, a better adjustment range of 0-2.5V (which seems reasonable, as the frequency of these VCXOs tends to increase with aging), and will also partially compensate for the tempco of the trimmer resistor.

author: floobydust
author_rank: Super Contributor
timestamp: March 24, 2025, 04:16:17 am
content: Your Rev. 0.0.3 schematic is wrong, check the resistor values.Proof is when the trimpot is at minimum resistance, it's overloading the shunt reg and it will drop below 2.5V

author: Uunoctium
author_rank: Frequent Contributor
timestamp: March 24, 2025, 12:35:51 pm
content: My modest contribution to this. Since the Vc input works on an internal resistance of 100kOhm, the preceding voltage divider with 1/20 should be sufficiently stable. I reduced the 'fine' regulator (15 turn) from 200 Ohm to 20 Ohm - otherwise 1/10 turn was enough to let the oscillator run away.

author: EU1
author_rank: Regular Contributor
timestamp: March 24, 2025, 01:20:37 pm
content: Quote from: floobydust on March 24, 2025, 04:16:17 amThe original 0.0.3 schematic does. 0.0.3 with my modifications should work fine.

author: bingo600
author_rank: Super Contributor
timestamp: March 24, 2025, 03:33:47 pm
content: Quote from: floobydust on March 24, 2025, 04:16:17 amI just read my res values/labels on my (today) received Rev 0.0.3 boardhttps://kiloohm.info/eia96-resistor/96CCode:R1 : 30D - 200KR2 : 01B - 1KR3 : 242R4 : 332R5 : W 204R6 : 68B - 4K99R7 : 512R8 : 18R0R9 : 18R0R10 : 18R0Seems to correspond w. the above 0.0.3 schem.