cti ocxo low in freq - Page 1
Forum section: electronics / beginners

author: ME
author_rank: Frequent Contributor
timestamp: February 16, 2025, 11:01:13 am
content: I have a chinese 10Mhz cti ocxo ,It is running at 99999861Hz not 10MHz as per spec, this is after doing the mods as per pic and after running for an hour, any ideas what to try next to raise the frequency to 10Mhz?

author: 807
author_rank: Frequent Contributor
timestamp: February 16, 2025, 11:37:55 am
content: My reverse engineered circuit is different to the one provided by Transradio. I had to reduce R1 & R3 in my case, as my oscillator was running high, rather than low. In your case you may need to increase R1 or R3 (or both), or decrease R2 to provide more voltage on the Vref pin.

author: SteveThackery
author_rank: Super Contributor
timestamp: February 16, 2025, 02:14:05 pm
content: Out of interest, what is the accuracy spec for that oscillator?Another question: what are you measuring its frequency with, and are you sure of its accuracy?

author: ME
author_rank: Frequent Contributor
timestamp: February 16, 2025, 02:27:10 pm
content: I am measuring with an advantest tr5823,the specs are:DescriptionReport ItemOCXO-10MHz rate reference source:Current consumption: preheating stage <750mA, working stage <300mAPreheating time :≈5 minutesCalibration accuracy :±001HzFrequency stability :5e-12Output level :dBm: 10dBmt2dBmas09;VRMS:07071V@5022:VPeak: I.0V@502:VP-P:20Va502.Output impedance :50ΩInterface type :SMA outer screw inner holeProduct Usage: constant temperature 0MHz ultra-low phase noise, frequency reference module, frequency reference source,OCXO rate reference source, used for sound system, decoder, shortwave radio, frequency meter, signal source and other instrument reference.as its so small with tiny resistors, I am thinking of doing a rebuild on a new custom pcb using a tl431.

author: SteveThackery
author_rank: Super Contributor
timestamp: February 16, 2025, 05:57:39 pm
content: I have a question about OXCOs in general, if anyone can help.What is the purpose of the Vref input? If it is to adjust the frequency, then doesn't that mean that the device doesn't meet the published specs until the user has tweaked it?If so, I don't understand. I thought an OXCO was supposed to be usable as a high accuracy, high stability frequency reference. But if the customer needsanotherfrequency reference to set it up... well, isn't that defeating the purpose?And how much is the frequency affected per volt or millivolt on the Vref pin? Does the Vref input need connecting to a precision voltage reference with a guaranteed stability in order to ensure the requisite frequency stability of the oscillator?In my ignorance I always thought that when you bought an OXCO precision frequency reference it would meet the stated accuracy and stability specs straight out of the packet.

author: ME
author_rank: Frequent Contributor
timestamp: February 16, 2025, 06:05:35 pm
content: any ideas of a ballpark value of resistors to try?, The max i can get at the vref pin is 7.8v. Thats with the pot at max travel,its cw as i turner the pot around thru 108 deg on the pcb so cw increases the freq and ccw decreases it.

author: floobydust
author_rank: Super Contributor
timestamp: February 16, 2025, 06:25:34 pm
content: Quote from: 807 on February 16, 2025, 11:37:55 amNewer boards (REV.0.0.2) come with a 200k trimpot instead of a 100k. You can read the "204" on the top marking. The other resistors are the same.It gave a V_CTRL of 1.95-2.15V span, which did not do much of anything towards changing frequency, although my resolution was only 8 digits at the time.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.Quote from: ME on February 16, 2025, 06:05:35 pmUh this is a 5V part and what are you doing measuring 7.8V there? Something wrong there.

author: hgl
author_rank: Regular Contributor
timestamp: February 16, 2025, 08:09:07 pm
content: Quote from: ME on February 16, 2025, 02:27:10 pmAlternative facts or misinterpretation of ppb ? ;-)

author: edpalmer42
author_rank: Super Contributor
timestamp: February 17, 2025, 03:49:28 am
content: Quote from: ME on February 16, 2025, 02:27:10 pmHave you checked the accuracy lately by comparing it to a known standard like a GPSDO, off-air standard broadcast, etc.? Even the best equipment will give bad results if it's out of adjustment.Do you remember when they launched the Hubble Space Telescope? All the pictures were blurry. It turned out that they'd checked the mirror by two methods. The low precision equipment said that the mirror was bad. The high precision equipment said the mirror was good. It turned out that the high precision equipment was completely wrong because it was out of calibration.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 17, 2025, 04:02:01 am
content: Quote from: SteveThackery on February 16, 2025, 05:57:39 pmCrystals drift. Always. Forever. Can't predict the direction or magnitude, no matter how hard you try, although you can say that it will probably stay within a range. Today, the frequency might drift up, tomorrow down.The higher quality oscillators are the hardest ones to deal with. They can be absolute divas! Don't shake it. Don't breathe on it. Don't let a sunbeam fall on it. Pretend it's full of nitroglycerine!Some oscillators have to run for 90 days before they meet their published specs. If the power even glitches during this period, the aging can completely change.Of course this CTI oscillator isn't in the same class as the divas. So the most likely possibilities are that it's just broken or that the frequency counter is out of adjustment.

author: SteveThackery
author_rank: Super Contributor
timestamp: February 17, 2025, 09:38:13 am
content: So you should set Vref to pull the oscillator to the correct frequency? How sensitive are they, typically, in terms of Hz per volt? That doesn't appear in the quoted specs

author: ME
author_rank: Frequent Contributor
timestamp: February 17, 2025, 10:15:17 am
content: my post of the max vref voltage was a typo,it should of said 2.376v,thats with the 100k pot at max travel ok.

author: ME
author_rank: Frequent Contributor
timestamp: February 17, 2025, 10:27:46 am
content: if i make a new pcb for this,would i be better of using a 7805 to power it with its tab soldered to the ocxo can, provided the can is only floating or common to gnd?, just thinking in terms of thermal stability?.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 17, 2025, 10:54:51 am
content: A 7805 is a regulator, not a voltage reference so that will not be stable enough I think.The 'official'(?) pdf says the following about the tuning range:0V: -2.0 ~ -1.0ppm2V: -0.2 ~ +0.2ppm4V: +1.0 ~ +2.0ppm1ppm on 10Mhz is 10Hz (if I had enough coffee already)https://dl6gl.de/media/files/ocxo-cti-osc5a2b02-datasheet.pdf

author: ME
author_rank: Frequent Contributor
timestamp: February 17, 2025, 11:21:23 am
content: What i meant was keeping the lt1009 but using the 7805 in place of its original vreg (lm2940s-5) but have the tab of the 7805 soldered to the osc can.

author: SteveThackery
author_rank: Super Contributor
timestamp: February 17, 2025, 01:03:25 pm
content: Quote from: PA0PBZ on February 17, 2025, 10:54:51 amSo it looks like there is no chance of the OP's OCXO reaching 10MHz using Vref. 9999861Hz* is 139Hz low, which is 13.9ppm. Is that right?The spec sheet says Vref can pull the oscillator over the range +2ppm to -2ppm. So -13.9ppm is way too much to be fixed with Vref. Looks like it's faulty, or maybe the OP's Advantest TR5823 has gone out of spec.*Did anyone else notice that the OP seems to have added an extra 9?Quote from: ME on February 16, 2025, 11:01:13 am

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 17, 2025, 01:58:36 pm
content: Quote from: SteveThackery on February 17, 2025, 01:03:25 pmThere's either an extra 9 or OP forgot a dot and it's really 9999986.1Hz which is a lot closer to 10MHz, the TR5823 has 8 digits afaik.

author: CaptDon
author_rank: Super Contributor
timestamp: February 17, 2025, 02:01:28 pm
content: Do I recall correctly from other threads on EEVBLOG that these units are 'fall outs' from the O.E.M. that didn't meet spec in the first place? Did someone raid a dumpster full of these non-conforming OCXO's. Anyone old enough to recall the days of 'Budget' vacuum tube suppliers buying fall outs from the major brands GE,RCA, Sylvania and Raytheon and rebranding them as names like TelRad, RadTel, Universal, KenRad and a hundred others? Usually sold at drug stores where there was a big 80 socket tube tester that mostly measured emission and possibly shorts. Fun times. The new tubes could be worse than your old ones!!

author: CaptDon
author_rank: Super Contributor
timestamp: February 17, 2025, 02:08:17 pm
content: I think we also want to know when the O.P. last verified the accuracy of his counter? I have a Tek 500 series counter module that is very accurate but only after a 4 hour warm up. It has an OCXO and it will actually overshoot two times during warm up and then settle down. The nice thing is after warm up it always falls within +/- 1Hz with a 15MHz reference. I have a 15MHz PLL locked to WWV as my bench reference.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 17, 2025, 04:48:20 pm
content: Quote from: SteveThackery on February 17, 2025, 09:38:13 amDatasheets rarely, if ever, state Hz per Volt. The one posted by hgl states that the tuning slope is positive (higher voltage = higher frequency), lists the tuning voltage range, and lists the overall tuning range in ppm. This is a fairly typical format for the information.So, you power up the oscillator, wait a day or two for the initial warmup & stabilization and do an initial adjustment of the frequency. Wait a day or a week and repeat. Is the aging dropping? Good! Eventually, the aging will stabilize at some value and you can, if necessary set up a monthly, quarterly, or whatever task to tweak the oscillator. In the case of a GPSDO, the feedback loop will keep the oscillator on frequency but you still might want to tweak the tuning voltage to ensure that the loop doesn't run out of range. Depending on the unit, you might have both a mechanical and electrical adjustment. Mechanical adjustments typically have more range, but less resolution than an electrical adjustment. i.e. the mechanical adjustment can be thought of as 'coarse tuning' while the electrical adjustment is 'fine tuning'.

author: 807
author_rank: Frequent Contributor
timestamp: February 17, 2025, 10:47:30 pm
content: Quote from: SteveThackery on February 17, 2025, 09:38:13 amIn my particular case, I could adjust the Vref voltage between 1.9400v and 2.1085v. This corresponded to a frequency of 1.80Hz and 3.49Hz above 10MHz. So a 1.69Hz change for a 0.1685v change. That's 10Hz/v. I didn't take any measurements between those min/max readings, so don't know if it was a linear change. Assuming it was linear, I calculated that I needed around 1.76v for 10MHz.

author: 807
author_rank: Frequent Contributor
timestamp: February 17, 2025, 11:35:17 pm
content: Quote from: SteveThackery on February 16, 2025, 05:57:39 pmAny type of Xtal oscillator is a secondary standard & will need tweaking to get it close to 10MHz. The OCXO is the better of the Xtal oscillators, but it needs to be compared to a higher order standard. The link shows comparisons between different oscillators. The primary standard being Caesium (or is it Hydrogen MASER these days?). There's also GPSDO to consider but it's not included in the table.Many items of test gear such as frequency counters have OCXO timebases, but you still see a hole in the back of the case to trim it (or in some cases it's trimmed in software).https://www.sciencedirect.com/topics/physics-and-astronomy/frequency-standard

author: ME
author_rank: Frequent Contributor
timestamp: February 18, 2025, 01:01:08 am
content: So is changing the original vreg to a lm-7805 and mounting its tab to the ocxo a good idea?.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 18, 2025, 05:04:50 am
content: Quote from: ME on February 18, 2025, 01:01:08 amWhy? It won't help you get the oscillator on-frequency, if that's what you're thinking. If it really is 139 Hz (14 ppm) low, the OCXO is broken and nothing will fix it. The datasheet shows that it only has a tuning range of 2 ppm.In general, you don't want to add or remove heat from an OCXO. It's designed to have a certain amount of heat transfer from the oscillator to the environment. If you change that, the oven temperature control circuit will be disrupted.Has it been powered up for the past few days? Has the frequency drifted towards 10 MHz?Have you checked your TR5823?

author: ME
author_rank: Frequent Contributor
timestamp: February 18, 2025, 06:32:59 am
content: The only way i have to check my tr5823 is a very old thandar tf-200,that gives nearon the same readings,guess i need to buy a gpsdo!,thanks all.

author: ME
author_rank: Frequent Contributor
timestamp: February 18, 2025, 06:40:32 am
content: I was thinking having the vreg tab thermaly fixed to the ocxo would make the whole caboosh more stable as in theory should the oven then not control the temp of the vreg as well sort of, Or am i missing something?.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 18, 2025, 08:09:57 am
content: Quote from: ME on February 18, 2025, 06:32:59 amDo you have or can you borrow asynthesizedsignal generator that will accept an external 10 MHz reference? If so, you can use your OCXO as the generator's reference and then use the generator's output to interfere with an off-air radio signal. By zero-beating the signals you can determine if your oscillator is on-frequency.For example, if you have a local station at 1 MHz, tune the generator to 1 MHz and with a short piece of wire as an antenna, you should hear some noise over top of the local station. If your oscillator is lower than 10 MHz, you'll have to adjust the generator up in frequency to get the same effect. It's a very cool effect!Here in North America we're spoiled by having WWV at 10 MHz. We don't have to use a synthesized generator, we just need a radio. A piece of wire attached to the OCXO's output would broadcast enough of a signal to hear the interference as a loud squeal in the radio. By tuning the OCXO to minimize the pitch of the squeal it's easy to adjust the OCXO. If the radio has a signal strength meter, you'll see the meter rise and fall when your OCXO is within a fraction of a Hertz of WWV's frequency. Ham operators have used this trick for decades.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 18, 2025, 08:15:42 am
content: Quote from: ME on February 18, 2025, 06:40:32 amNo, the surface of the OCXO will be much cooler than the oscillator's core. Some oscillators have insulation around the oven, some just use an air gap. Regardless, they won't appreciate it if you ask them to try and keep something else at a constant temperature. The heating circuit is only designed to keep the crystal and sometimes the core oscillator circuitry at a constant temperature.

author: SteveThackery
author_rank: Super Contributor
timestamp: February 18, 2025, 11:01:47 am
content: Quote from: ME on February 18, 2025, 06:40:32 amYour OXCO is off by 139Hz (14ppm).That means it is faulty.There is little more to be said, and especially it is pointless messing about with bodging in a 7805.The Vref input can only affect the frequency by -2 to +2ppm. That is less than the 14ppm error, so you can forget about fiddling with Vref - it's flogging a dead horse.Either the OXCO is broken, or your Advantest TR5823 is way out of calibration. Assuming the former, the only way forward is to buy another.

author: 807
author_rank: Frequent Contributor
timestamp: February 20, 2025, 11:27:12 pm
content: @ME...you never clarified the actual reading you were getting on your frequency meter. You stated it was 99999861Hz, which is nearly 100MHz. Did you add an extra 9 at the beginning, meaning that the oscillator was 139Hz out, or did you mean 9999986.1Hz, meaning the oscillator was only 13.9Hz out?

author: shabaz
author_rank: Frequent Contributor
timestamp: February 21, 2025, 12:47:35 am
content: Quote from: SteveThackery on February 18, 2025, 11:01:47 amIt's also expected that some may be faulty, since it's likely not much care is taken extracting them from their old equipment. It makes sense to buy (say) at least half a dozen or more, since they are (relatively) low-cost, and try each one, fully expecting some to need to be thrown away. I think I purchased 20 (still costs less than a couple of $ per oscillator) and will be happy if just one or two work out great. I have not got around to doing anything with them yet, since I don't have any decent strategy thought out how to set up the test for trying several of these at a go.

author: BillyO
author_rank: Super Contributor
timestamp: February 21, 2025, 09:38:09 pm
content: Quote from: CaptDon on February 17, 2025, 02:01:28 pmNot all of them, if any. The ones I got a couple of years ago were from upgraded cell tower equipment. China did a huge upgrade of their cell infrastructure a few years back which caused a flood of these on the market. That they are all "fall outs" strikes me as the result of the popular sport of Sino Phobia. The 10 I got all met their specifications without any issue.

author: ME
author_rank: Frequent Contributor
timestamp: February 22, 2025, 08:48:21 am
content: Quote from: shabaz on February 21, 2025, 12:47:35 amfwiw heres a pic of it on the counter.

author: BillyO
author_rank: Super Contributor
timestamp: February 22, 2025, 06:03:11 pm
content: Hmm, Advantest state the accuracy of the TR5823 as: +/- 1 count +/- timebase accuracy. However, they give no specification on base timebase accuracy for either of the available timebase option. However, they quote the aging at 5x10-7/ month. Depending on how far off it was when new, it could very well be considerably out of whack. I think the "error" you are seeing is a combination of both the counter being off and the OCXO being off.I would just try putting a 100K pot between 5V and 0V with the wiper going to the vref pin and see if you can adjust it to your liking

author: floobydust
author_rank: Super Contributor
timestamp: February 22, 2025, 06:57:34 pm
content: Oh... I see a varactor diode is used in OCXO's. My experience with varactor diodes is they age and drift badly, I kind of hate them as an unreliable beast.This would explain the used modules (pulls) that are grossly out of spec or that do not respond much to their tuning voltage.edit: these teardown pics of the OSC5A2B02 don't seem to show a varactor diode. Mainly an ASIC with "303" or "501" markings, SOIC-16W (wide body).Schematic of larger CTS 10MHz OCXO 1960017 (taken fromThe Sync Channel Blog) uses SMV1237 varactor diode SOT-23.

author: ME
author_rank: Frequent Contributor
timestamp: February 23, 2025, 12:38:51 pm
content: Well heres an update on this turd, I decided to have another look at this, I tried two different counters and none was counting just reading zeros!, I thought i would have a poke around with my scope, Both sma outputs on the pcb have no outputs!, The only signal i get is on the nc pin on the ocxo block, its a clean sine wave at just over 1mv peak to peak, I guess this ocxo was on its last legs when i got it and has finaly died,I am waiting for a refund from aliexpress after i asked for a refund and they found in my favor, Does anyone know a decent seller for these so i can order a replacement, I even tried hooking up a pot like mentioned a few posts back, That allowed me to adjust the vref pin from 0v to 2.4volts but no joy!.?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: February 23, 2025, 01:29:59 pm
content: Bought 4 pcs bare OXCO's from this seller. Came without the pcb fragments.https://www.ebay.de/itm/144769640308Project is upgrading an very old fashined Yaesu YC500s (late '70) which is totally out of spec with the build in Toyocom TCXO.That's mine solution – reading is stable over a dozen of hrsWiper of pot is aprox at 2/3 upper position

author: SteveThackery
author_rank: Super Contributor
timestamp: February 24, 2025, 01:21:49 am
content: Quote from: ME on February 23, 2025, 12:38:51 pmWhy the question mark? We've explained this already. That Vref pin can only adjust the frequency by +/- 2ppm; your OXCO is off by 14ppm. Hence the no joy. Is there something unclear about this?

author: shabaz
author_rank: Frequent Contributor
timestamp: February 24, 2025, 04:07:50 am
content: They are (practically) a black box, if it doesn't work and you're convinced you're using it right, then you may need to try a different one.Someone I trust tested about four or five of them, and although they all generated output, the best of that bunch had a ten- to twenty-fold difference in stability over a period of time, compared to the remainder. If that matters to you, then you'll likely need to try more than one.I don't have a full strategy nor the complete test equipment for it (for instance, a GPS disciplined oscillator to be able to trim the end frequency), hence why mine are waiting as a back-burner project for when I do have the knowledge/capability.But even from a five-second visual inspection, you can see that the best care was not taken in extracting and storing them. I'm not saying that doesn't make it worthwhile, but you have to be pragmatic and simply accept that not all will function (or function well).

author: floobydust
author_rank: Super Contributor
timestamp: February 24, 2025, 05:01:27 am
content: I think each of these modules has been tested and ranked after being pulled.The oddball mini QR code on the underbelly- it's the wrong place for them, is unique for each module, and as a thermal label none would survive reflow - although I'm sure these modules are not compatible with reflow processes.So what is this QR about then?I saw one module taken apart and with no glue, leaving an air gap between the thermistor and thermal plate inside. That can't work very well lol. Other's have glue. So there might be a quality problem with some.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 24, 2025, 05:34:44 am
content: You're right, they may have done a go/no-go test and measured frequency maybe at low/high control voltages, but a stability test would take a long time, so it's probably economically unviable for that to have been done and anything thorough at the low cost they were charging.I'm willing to take apart one or two of these units to see what's inside (it might take me a few days to find some time, unfortunately). It will be interesting, anyway, just to see how similar this lot looks inside compared to other examples on the 'net.

author: CaptDon
author_rank: Super Contributor
timestamp: February 24, 2025, 01:51:00 pm
content: As mentioned before and in different threads on EEV, these are pullouts being sold at two cents on the dollar of their original purchase price. The best of the best pullouts are probably being bought up and used by the Chinese military and the rest being dumped to eWaste marketers. You get what you pay for and from whom you are buying. Adjustable by +/- 2ppm but off by better than 10 ppm after warmup?You bought yourself some expensive target practice. Add this thread to the many others concerning TCXO / OCXO devices with very poor or totally unacceptable performance.

author: 807
author_rank: Frequent Contributor
timestamp: February 26, 2025, 02:46:45 pm
content: As I mentioned in one of the other threads, if you want to see what's inside, IMSAI Guy took one apart...

author: floobydust
author_rank: Super Contributor
timestamp: February 26, 2025, 09:26:09 pm
content: Do we know who makes the ASIC? That video it's a "303" but recent teardowns it's a "501".I note these VCOXO's modules sell for $100-$200 typically. So an entire board for $20 suddenly looks attractive, even if I have to cut open the thing and repair it lol.

author: ME
author_rank: Frequent Contributor
timestamp: February 26, 2025, 11:55:03 pm
content: Well i have ordered 5 bare osc cans,the lot were only £5 ish, Also ordered a gpsdo , We shall see what the next lot are like, aliexpress for some reason aggreed with my refund then had an email saying final solution=no refund!, Not sure why, does anyone know if the xtal can be changed in these for different freqs?.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 27, 2025, 12:50:00 am
content: I decided to take one apart. I appreciate there are already teardowns out there as someone mentioned, but I'd rather take my own hi-res photos.It turned out to be just a three-minute task, using a Dremel cutting wheel.I have not had a chance to look in detail at the photos yet, but they are attached.This OCXO was purchased in March 2024.EDIT: The transistor on the underside is 2SD1803, and you can see what looks like it may be an RTD or thermistor, between the transistor and the crystal. The crystal, transistor and that temperature sensor are all bonded together and to the metal plate, on top of some insulator that looks finely corrugated.

author: floobydust
author_rank: Super Contributor
timestamp: February 27, 2025, 01:16:41 am
content: I would guess the zener "B9", or crystal or ASIC have drifted somehow causing the frequency to be off. How the freq. is skewed by the control voltage, varactor diodes live somewhere. The tantalum looks OK.I'm not sure of the oven target temperature for the crystal - but the outside QR code includes the crystal marking label as well. Hmmm.Did you notice the oddball PCB layout for pin 2? It floats in space lol.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 27, 2025, 02:39:02 am
content: Best I know, the things from Ebay / Ali / China are second hand OCXO (are you sure it has an oven? I don't trust what the cinese print on stuff) and salvaged from old equipment. The thing may be 10 or 20 years old and "well aged". If it's out of spec now I guess you're just out of luck and you'd better try another one. Also look at the scratches and dents on the photograph posted by shabaz. Does that look like new stuff to you?You can of course always try to increase the adjustment range on the trim pin and see how far you can get. But even if you manage to get it within spec, how long will it stay that way? Once it starts drifting it's probably simply reached the end of it's life.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 27, 2025, 05:42:25 am
content: Quote from: floobydust on February 27, 2025, 01:16:41 amHi, yes just noticed that pin 2 now! It's unsoldered as you say.Just out of general curiosity I tried buzzing out parts of the circuit just now, and I believe the black boxes are small chokes (doesn't feel like ceramic, but might be plastic potted), the top SOT23-5 part (90SM) is likely a voltage regulator (that tantalum positive end is connected to it too), and possibly the oscillator output is pin 1 on the main IC (I'll power it up at some point and confirm), and DC is going into pin 1 too (via one of those chokes).Presumably the lower-left SOT23-6 is an amplifier or RF switch maybe.The power NPN on the other side is simply directly across the power rails.

author: ME
author_rank: Frequent Contributor
timestamp: February 27, 2025, 07:58:50 am
content: Is the xtal in the teardown pics a 10Mhz unit, can it be changed for another freq?.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 27, 2025, 03:32:05 pm
content: Hi,Ordinarily it wouldn't be advised to swap for a different frequency for various reasons. One reason is that the oscillator circuits are intended for a particular ballpark, so if you use a crystal of significantly different frequency, it may not oscillate.Another reason is that things are designed around using a particular reference and then constructing any other precise frequency from that (with a frequency synthesizer).If your requirement is to simply have a reasonably precise frequency signal source at an arbitrary frequency, you may wish to consider one of various PLL or DDS frequency synth boards (often very low-cost from AliExpress), or ICs (if you wish to build from scratch). A few examples are AD9954 (very easy-to-use for generating signals up to 160 MHz or so), MAX2870 (various boards on AliExpress, usually with a touch-screen fitted, for approx. 28.5 MHz upward into microwave), or even a very low cost Si5351 (useful up to a couple of hundred MHz approximately, a little awkward to program from scratch, but there are dozens of libraries, including for Arduino and so on). Some of these boards may use a TCXO for their internal reference; others may allow connection of an external 10MHz reference.

author: ME
author_rank: Frequent Contributor
timestamp: February 28, 2025, 10:18:05 am
content: I may cut mine open and change the xtal and see what happens, It seems to be dead anyway so nothing to loose. It was low in freq anyway so guess the xtal was in its death throws, think i will cut the xtals legs and tack another xtal to the remains and see if it restores output on the output pin just for a test.

author: ME
author_rank: Frequent Contributor
timestamp: February 28, 2025, 09:54:51 pm
content: Well i cut this open, What looks like a vreg has a bleb and a burn hole, Its dead jim dead!.

author: floobydust
author_rank: Super Contributor
timestamp: February 28, 2025, 10:12:26 pm
content: Which IC is blown? I thought your module worked but freq was low?WS06 flipped90SM LDO w/ref cap, or 1ACL Tinylogic, or ASIC 501?We have to figure out the VCOCXO ASIC IC, it's either "501" or "303" maybe NDK makes it. I can't find this mystery IC. Could conquer it and draw a schematic if we have that info.One dud module I have is centered high in freq. (32Hz 3.2ppm) and the control voltage does nothing over a wide window. It doesn't seem to pull the crystal unless the voltage is far out there like 0.4V or 4.5V so I suspected a varactor diode got old, it must be in the ASIC.I'm not sure what happens with old crystals, how they behave. These modules have a selected crystal in them I think, QR code tracked.Precision 2ppmTaitiencrystals are $45 at DK.I'll just order more modules for the fun.edit: had SMT marking code upside down.

author: ME
author_rank: Frequent Contributor
timestamp: March 02, 2025, 01:34:43 am
content: The blown ic is top left in pic, As far as i know xtals go down in frequency as they age.

author: ME
author_rank: Frequent Contributor
timestamp: March 02, 2025, 01:39:43 am
content: the pic rotated so the dead ic is now lower left, Whatever it is has 6 legs.

author: floobydust
author_rank: Super Contributor
timestamp: March 02, 2025, 08:36:51 pm
content: That burnt IC is the output buffer SOT-23-6 "1ACL" or "1ACW" likely a tiny logic part 74LVC 5V inverter etc. but I could not find the marking code.The IC on the other side is the voltage regulator SOT-23-5 "90SM" and I couldn't find it either. "90S" is Ricoh RP104N311B LDO but it has no low noise ref pin for the cap.The ASIC could be Seiko NPC or NDK, I suspect these are Japanese manufacturer.It's even possible to be using a 20MHz xtal and a divide by two.Module Pin 1 OUTPUT is the square corner, not the rounded corners.Did see a patentUS 6628175Pericom "Voltage-controlled crystal oscillator (VCXO) using MOS varactors" for the VCXO function. I think the ASIC is using these.

author: ME
author_rank: Frequent Contributor
timestamp: March 06, 2025, 03:35:20 pm
content: I received 5 new tcxo bricks today, I removed the resistors and pot from the frequency ref chinese pcb ,I then glued the pot on the rear of the pcb with one outer leg to ground the center leg to the vref leg on the tcxo can and the other outside leg of the pot going to the 2-5v output leg of the lt1009, I hooked this upto my scope on one channel and my 10 Mhz gpsdo onto ch2,after turning the pot i get the traces locked with eachother,see pic, Does that mean its working ok ?.

author: floobydust
author_rank: Super Contributor
timestamp: March 06, 2025, 04:49:45 pm
content: I think that's one way to see if the module under test is ballpark for frequency.You would trigger the scope off the GPSDO and look at the module under test to see if the trace is rolling. But any rolling could be super slow to observe and jitter from the scope's trigger section I think could make things fuzzy? You should see moving until both are stable.What module control voltage do you measure when it's set to match?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: March 06, 2025, 07:02:53 pm
content: "Accuracy = (for a one-cycle drift)1 second drift/cycle = 10^-7; 10 second drift/cycle = 10^-8; 100 second drift/cycle = 10^-9"Source: xl microwave 3400 counter manual, Calibration: see P.54https://www.ko4bb.com/manuals/88.73.135.189/3600-3400_40-60GHz_Counter_w_Powermeter_Service_Manual.pdfAnd according to their drawing, they also use an TEK475

author: ME
author_rank: Frequent Contributor
timestamp: March 06, 2025, 08:29:27 pm
content: Quote from: floobydust on March 06, 2025, 04:49:45 pmSo do i just make sure to say have the gpsdo on ch1 the chinese jobby on ch2 but set the scopes trigger to ch1?.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: March 06, 2025, 08:42:36 pm
content: calibration against a reference standard is precisely described in the mentioned xl-microwave manual

author: ME
author_rank: Frequent Contributor
timestamp: March 06, 2025, 09:03:31 pm
content: Well i dont have any microwave manuals apart fro the one for heating my food!, I triggered from boh chanells and triggering from either gave a rock steady trace in respect of each other so guess its ok then?, the only thing of note is it draws 260ma after a few mins warmup and not 250ma as per the datasheet.

author: floobydust
author_rank: Super Contributor
timestamp: March 06, 2025, 11:21:11 pm
content: Quote from: ME on March 06, 2025, 08:29:27 pmYes, that's pretty much it. I'm assuming that you are only looking for ballpark frequency, in order to determine if a module is in spec. and not way off in frequency. Just like tuning into WWV and using a beat frequency I think. Timenuts would not like this method for any great sub-ppm accuracy.From the XL Microwave manual:5-7. REFERENCE OSCILLATOR ADJUSTMENT [stuff deleted...]5-7.2. Allow the instrument to warm for three (3) hours for the TCXO, 24 hours for the OCXO...5-7.3. Two ways are given to calibrate the counter’s internal reference oscillator. The first way (analog) is simpler, requiring only a scope and a traceable frequency standard. It also offers instant visual feedback of the result of the tuning adjustment. The second way (digital) requires more equipment but is faster and yields a more accurate number.5-7.4. Analog. You will need the following test equipment from Table 5-1: a100 MHz Oscilloscope and a traceable 10 MHz Frequency Standard. Connect the equipment as illustrated below in Figure 5-1.Figure 5-1. Reference Oscillator Test Setup, analog version.5-7.5. Set the scope to show 1 to 5 cycles of a 10 MHz signal. Connect the 10 MHz signal from the frequency Standard to Channel ‘A/1’ of the scope and trigger on Channel ‘A/1’. Connect channel ‘B/2’ of the scope to the ‘REF OSC OUT’ BNC connector on the back of the counter. Watch the scope’s display and note the time it takes for one complete cycle of channel ‘B/2’ to drift one cycle compared to channel ‘A/1’. On the Oscillator CCA (5999-45561, figure 6-6) adjust the ‘Oscillator Trimpot’ (RA1) for minimum drift of the signal on the oscilloscope display using a nonconductive tuning tool (remove the tool when noting drift as the tool will affect the observation). Accuracy = (for a one-cycle drift)1 second drift/cycle = 10-7; 10 second drift/cycle = 10-8; 100 second drift/cycle = 10-9.

author: ME
author_rank: Frequent Contributor
timestamp: March 07, 2025, 12:24:38 pm
content: I would like to build a pcb around my new ocxo cans using eagle, does anyone know where i can get an eagle footprint for the CTIosc5a2b02 ocxo ?, thanks.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 08, 2025, 02:58:05 pm
content: Quote from: ME on March 07, 2025, 12:24:38 pmIn many (most/all) PCB design packages you can make your own footprint, otherwise an oddball part would leave you stuck. My own favourite software is Sprint Layout by Abacom, it is about 49 Euros.SJ

author: Gyro
author_rank: Super Contributor
timestamp: March 08, 2025, 03:30:00 pm
content: Quote from: Solder_Junkie on March 08, 2025, 02:58:05 pmThe OP double-posted a separate thread on the subject...https://www.eevblog.com/forum/eagle/cti-osc5a2b02-eagle-footprint/

author: alex843
author_rank: Contributor
timestamp: March 30, 2025, 12:12:40 pm
content: Quote from: ME on February 27, 2025, 07:58:50 amYou might be able to replace the crystal, but it's good to remember that the common AT-cut crystal resonators that you can purchase for most radio and microprocessor applications are optimised for stability at room temperature, while the ones used in the OCXO are likely to be SC-cut crystal resonators designed for the higher temperature oven controlled oscillators.There are other OCXO frequencies that you find for sale if you want them, including:13 MHz used in GSM base stations- 13 MHz/48 = 270.83 kHz which is the GSM Air Interface bit rate.- 13 MHz/65 = 200 kHz, the GSM radio channel spacing.38.88 MHz used in SDH/SONET/ATM optical systems- 38.88x4 = 155.52 Mhz, the STM-1 line rate- 38.88x16 = 622.08 Mhz, the STM-4 line rate.I've also seen some 20 MHz and 40 MHz OCXO for sale.

author: ftg
author_rank: Frequent Contributor
timestamp: March 31, 2025, 07:44:18 am
content: Other two cheap OCXO frequencies are 26MHz (also used in GSM base stations, that's where all of mine came from) and 30.72MHz, used in LTE base stations.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: April 03, 2025, 07:11:06 pm
content: Only for the protocoll.I now tested or installed all 4 that I purchased last year. Or repaired them.Result: 2 DoA!One without heating, a second with distorted output signal (rather sawtooth). I replaced the heating transistor with 2SC5706, but draws a slightly higher current (600..700mA in the first heating phase).The distorted output was caused by the Inverter/Schmitt ( bottom left corner). I threw in what was available in the workshop, 74SU04 -two pins reversed -, square yes, but round corners and wrong duty cycle – too slow, no HCT. Doesn't matter, because in the target device anyway only sine works. That comes for free, because at input of inverter is a pure sinewave, but only 150mVpp. Wired it to the free (NC) contact.There seem to be very different versions, because in contrast to the pictures here in the thread, mine all had a TSSOP-20 chip instead of -16. And the supply of the output buffer is either direct wired to U(unreg) (the one with the defective output buffer) or behind the 3V3 regulator and so protected against overvoltage.Differences in the tuning voltage are also huge: 2 x 1.8 V, 1x 1.4 V and 1x 2.02 V.

author: bingo600
author_rank: Super Contributor
timestamp: April 06, 2025, 06:05:36 am
content: Just attached the "interesting" Cal. page from the counter manual above

author: BillyO
author_rank: Super Contributor
timestamp: April 06, 2025, 02:02:28 pm
content: Quote from: bingo600 on April 06, 2025, 06:05:36 amYup, that's how it's done.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: April 10, 2025, 04:51:10 am
content: By the way, the tech nerds at HP also count seconds