frequency standard ideas ? - Page 1
Forum section: electronics / projects

author: Flump
author_rank: Frequent Contributor
timestamp: May 12, 2014, 12:02:33 pm
content: i use a precision 5v regulator and 0.01 % resistor to check my multimeters withbut i would like something to check the frequency accuracy of them (those that have freq testing)and also to check the accuracy of my scope.So I would like to make a very basic and simple frequency standardnot sure of the frequency yet, i guess it depends if there is cheap pre madesolution but anywhere from 100hz to 1mhz i think.anyone got any idea for a simple diy solution ?

author: dfmischler
author_rank: Frequent Contributor
timestamp: May 12, 2014, 12:07:57 pm
content: It depends a lot on how accurate you feel you need to be. Will you be happy with 10 ppm (i.e. off by up to 10 Hz at 1 MHz)? Or do you feel you need to be 1000 times that accurate?Maybethis articlewill give you an idea.

author: jpb
author_rank: Super Contributor
timestamp: May 12, 2014, 12:28:45 pm
content: If you want to avoid calibration, then you need to compare to a GPS which at the 1Hz (1pps) are cheap (£25 or so new) or possibly to a calibrated Rubidium off e-bay which are now rather expensive.The U-blox LEA-6T is a timing GPS module that can be programmed to produce a frequency locked to the GPS from 0.25Hz to 10MHz though some frequencies have more jitter than others:http://www.u-blox.com/images/downloads/Product_Docs/LEA-6_DataSheet_(GPS.G6-HW-09004).pdfA module with the LEA-6T is around £100 off e-bay or a more sophisticated one is 181 Euro from sysmocomhttp://shop.sysmocom.de/products/osmo-lea6t-gpsNote these modules have quite a lot of jitter, though for testing scopes you won't notice it. (My cheap GPS module's 1pps has less than 10nsecs of jitter so is good to 8 decimal places - I tested the frequency counter on my scope and it read 999.998 mHz which I was quite pleased about as the scope's spec is quite a bit wider than that.)A cheaper option is to buy a OCXO from e-bay for around £10 to £20 but these will typically be 10MHz or 5MHz so you need to then build a divider circuit. Also the accuracy is not guaranteed so you may need to calibrate.I have a TTi 930 counter so what I did was get a 10MHz OCXO off e-bay and use it as the reference to the counter and then adjust it until it read the 1pps from my GPS module as having a period of exactly 1 second to 10 digits.

author: han
author_rank: Frequent Contributor
timestamp: May 12, 2014, 12:30:31 pm
content: just buy standard oscillator and divide it with flip flop or logic counter.http://www.digikey.com/product-detail/en/MXO45HS-3C-4M0000/CTX742-ND/1801857i can find one in old AT Motherboard(20Mhz one)

author: olsenn
author_rank: Frequent Contributor
timestamp: May 12, 2014, 12:56:41 pm
content: A ovenized crystal is probably all you need (if you even need that). Atomic (Rubidium) oscillators have poor short-term stability and are probably not what you're looking for (unless you need like 12-digits of resolution).

author: VK5RC
author_rank: Unknown
timestamp: May 12, 2014, 01:09:59 pm
content: +1 for the ovenised crystal, 10MHz is quite useful as later on you can use it as a frequency reference for other Lab equipment, some go quite cheaply on eBay if not an HP 8011 etc.http://stores.ebay.com.au/Rubidium-and-GPS-DO-From-China/High-reliability-OCXO-/_i.html?_fsub=202159619.I have bought from this guy before. If you have a friend with a good counter he can get its frequency very accurately for you.

author: linux-works
author_rank: Super Contributor
timestamp: May 12, 2014, 02:08:30 pm
content: Quote from: olsenn on May 12, 2014, 12:56:41 pmI'm not sure I understand; why do you think Rb is bad short-term?

author: Flump
author_rank: Frequent Contributor
timestamp: May 12, 2014, 02:16:18 pm
content: thanks for all your input so far guys.i stumbled across this on ebaycould i use this ?http://www.ebay.co.uk/itm/1-4-8-10-12-15-16-20-25-27MHz-Crystal-Oscillator-Osc-5V-H-DIP-/181176601343?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item2a2ef78affis it as simple as supplying it 5v and it outputs an accurate 1Mhz ?

author: linux-works
author_rank: Super Contributor
timestamp: May 12, 2014, 02:22:54 pm
content: the canned oscillators are easy; power, ground and signal-out.they may drift with voltage and temperature and you can buy various degrees of accuracy and precision.if you are looking for a 'standard' though, an oven or tcxo would be better than a simple can. plus, be careful buying 'precision' parts from ebay. ebay is all about fakes, these days. buy from a real distributor if you want to trust the device and be sure about it.

author: jpb
author_rank: Super Contributor
timestamp: May 12, 2014, 02:50:35 pm
content: Quote from: linux-works on May 12, 2014, 02:22:54 pmWith OCXOs the ones on ebay are pretty old and one issue with them may be that the Voltage tuning range has reached its limit (the oscillator has drifted beyond the range over a period of say 20 years). But the ones that I've bought have been ok - the main one I have tunes to 10MHz at around 2.7V in a 0 to 5V tuning range (the crystal itself provides 5V from its internal regulator so you can tune it with just a pot.)I think it is worth the gamble of getting OCXOx from ebay because they are generally about one tenth the cost of buying a new one. I recently bought a pair of 5MHz OCXOs on boards with tuning pots and rather nice minicircuit power splitters for £15 for the pair + postage bringing it up to £20 for the pair. I was the only person to bid but they work fine (I had to dig around to find what the components on the boards were and the specs and pin outs of the OCXOs themselves).If you do a search on ebay on OCXO several come up. The 5MHz are cheaper than the 10MHz because most modern equipment wants 10MHz as a reference so they are more popular.If you hang about a bit and are not in a rush then cheap and good condition local ones should appear from time to time if you don't want to risk importing from China.EDIT : perhaps I should qualify my remarks a bit. There are drawbacks with buying low cost OCXOs from ebay. One is they might be physically broken (the oven component) or more likely the device can't be tuned to the exact frequency (perhaps not a problem if your just using it as a test rather than a reference for a PLL in an instrument). Secondly these older OCXOs tend to be larger and more power hungry. They also often require 12V or even 15V or more and draw close to an amp when the oven is first warming up, dropping later to 200-300mA. This isn't a problem if you have a bench power supply and only want to power it up occasionally. It is more of a problem if you're trying to build a GPSDO you want to leave on for long periods (as I am) as the current draw is a bit non-green, though they are much less power hungry than a Rubidium.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 12, 2014, 03:47:31 pm
content: Quote from: linux-works on May 12, 2014, 02:08:30 pmMost cheap rubidium clocks use the Rb output to discipline a standard quartz crystal oscillator. The long term stability is great, but their phase noise in the 10 Hz to 1 MHz region is relatively poor and exactly what you would get from the same cheap crystal without the rubidium source. This doesn't matter for making the time base to a frequency counter but if you use it as an external clock for e.g., a spectrum analyzer or a frequency synthesizer, that noise will affect the performance. An OCXO has much lower phase noise, and is a better choice when spectral purity is more important than drift or absolute frequency accuracy. Higher end Rb oscillators like the stanford research units use an OCXO to get the best of both worlds.

author: linux-works
author_rank: Super Contributor
timestamp: May 12, 2014, 03:53:48 pm
content: while the Rb boxes are not technically oven controlled (most of the cheaper ones), they do have an oven effect in that they want to maintain a temperature and will fight to keep it.I understand the phase noise isn't as good as possible, but for many home labs, its the best freq standard we'll likely see.that said, some people want their home lab standards to run 7x24 and in that case, rb is entirely the wrong thing. too power hungry, runs too hot and the bulb wears out sooner that way.

author: G0HZU
author_rank: Super Contributor
timestamp: May 12, 2014, 07:27:07 pm
content: Quote from: Flump on May 12, 2014, 12:02:33 pmThe following should be more than good enough for nearly everybody:Find a surplus 10MHz OCXO on ebay or on an old PCB at an electronics fair. Try and get one with a digital output rather than a low level sine wave.Power it from a decent regulated and stable supply and buffer it and then use it to clock a series of /2 and /5 counters in a few 74HC390 based divider chips. These chips cost about 50p each and can get you various division ratios and you can tap out the output of each divider.So you could easily get 10MHz, 5MHz, 2MHz, 1MHz etc etc down to 100kHz from 1 74HC390 chip. Then go down another /100 in a second chip to reach 1kHz.The downside of the OCXO is that it could take anything up to 45minutes to stabilise after you first power it. If this is not ideal for you then try to find a 10MHz TCXO. Obviously, you won't get the same stability or accuracy over time with the TCXO but it is still going to be good enough for most people.There are 'fast' OCXOs available, eg I have one here that takes about 90 seconds to warm up but it obviously compromises the accuracy and stability in order to achieve this fast warmup time.I wouldn't really recommend the cheapy £3 oscillator on ebay because it will have 50ppm temperature stability but this could be on top of a 100ppm basic accuracy. For maybe £10 you could get a fairly decent 10MHz TCXO or OCXO.

author: linux-works
author_rank: Super Contributor
timestamp: May 12, 2014, 08:49:57 pm
content: save the dividers.google 'picdiv' for an 8pin dip to do the dividing for you.

author: dfmischler
author_rank: Frequent Contributor
timestamp: May 12, 2014, 08:53:52 pm
content: Quote from: Flump on May 12, 2014, 02:16:18 pmYes, it is very simple. It will probably be fine if 50 ppm is accurate enough.

author: gdewitte
author_rank: Unknown
timestamp: May 12, 2014, 09:52:31 pm
content: Perhaps this?http://www.aade.com/newfreq/new%20freq.htm

author: dannyf
author_rank: Super Contributor
timestamp: May 12, 2014, 11:56:32 pm
content: QuoteThe answer depends on what you meant by "frequency standard". Most (all?) of the multimeters utilized a crystal to clock its frequency measurement. That's typically 100ppm or better. So for measuring a typical LC/RC oscillator, it is more than sufficiently accurate, and nothing needs to be done there.If you want more, you can utilize pre-made oscillators. Most of the crystal oscillators are spec'd to 50 or 100ppm, and they usually are good to 10-20ppm. They are dirt cheap and requires a simple power / ground connections to get going.However, that approach really doesn't offer much beyond what your multi-meter can do. For better results, you may consider TCXO. Two flavors, analog-tuned or digitally-tuned. Buying an analog TCXO 2nd hand can be risky, if you don't have a high(er) accuracy frequency meter / counter to know exactly at what frequency it is oscillating. A digitally tuned TCXO needs no calibration and I would go with that. You can typically get within 10ppm spec-wise, and typically within 2-5ppm performance-wise - there are TCXOs that offer sub 1ppm spec but they are quite expensive.Note: Some of today's TCXOs are VC-TCXO - they are not that useful for what you do.OCXOs offer better performance but they consume a lot more current and are more expensive - I wouldn't buy them 2nd hand.

author: Unknown
author_rank: Unknown
timestamp: May 13, 2014, 12:46:36 am
content: Quote from: dannyf on May 12, 2014, 11:56:32 pmAny devices you'd suggest / recommend in the 1-100MHz range? I've seen the Maxim DS3231 etc., but 32.768kHz is a bit low for anything other than RTC uses.I'm not a time/frequency nut, but it'd be handy to have something like that in the parts box if the price is right.

author: rfdave#gmail.com
author_rank: Contributor
timestamp: May 13, 2014, 02:55:31 am
content: Quote from: ejeffrey on May 12, 2014, 03:47:31 pmThe actual Rb frequency measurement is at ~6.9 GHz, so all Rb clocks have an internal Quartz Oscillator that's locked to the Rb Oscillation. Expensive Rb clocks have better Quartz oscillators built in.

author: Flump
author_rank: Frequent Contributor
timestamp: May 13, 2014, 09:28:53 am
content: just looked ppm up on google and 50ppm = 0.005 i think ?http://www.rapidtables.com/convert/number/PPM_to_Percent.htmso 1Mhz could be999.95Hz to 1000.05Hzis that right ?I Ordered this just to see what its like, its very cheap sonothing lost if it doesnt work out righthttp://www.ebay.co.uk/itm/181176601343?var=480257110155&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

author: David Hess
author_rank: Super Contributor
timestamp: May 13, 2014, 10:05:57 am
content: Quote from: ejeffrey on May 12, 2014, 03:47:31 pmTheir phase noise is poor because they generate a synthesized, usually DDS, reference output. This is great if you want an adjustable output frequency but bad for phase noise compared to using a dedicated phase locked crystal oscillator which is unnecessary for most applications.

author: Flump
author_rank: Frequent Contributor
timestamp: May 14, 2014, 11:52:04 am
content: ok my oscilator came todaynext day delivvery cant grumble with thathttp://www.ebay.co.uk/itm/181176601343?var=480257110155&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649It works with my extech 330 dvm, that reports 999.6Hzbut its too output strength to read on my frequency counter.could i use a 2n3904 to amplify itand if so could anyone suggest a circuit please

author: dannyf
author_rank: Super Contributor
timestamp: May 14, 2014, 12:18:33 pm
content: QuoteYou probably want to make sure that it is an amplitude problem. Otherwise, use a transistor or a gate.

author: jpb
author_rank: Super Contributor
timestamp: May 14, 2014, 12:19:48 pm
content: Quote from: Flump on May 14, 2014, 11:52:04 amAccording to the specs in the link you provided it should be producing a square wave between 0.4V and 90% of 5V = 4.5V at least, this should be plenty large enough for a counter to read - it might be too high.Perhaps you need to ac couple it to the counter and even attenuate it a bit not amplify it.

author: David Hess
author_rank: Super Contributor
timestamp: May 14, 2014, 12:34:54 pm
content: Quote from: Flump on May 14, 2014, 11:52:04 amWhat make and model of frequency counter is this?

author: Flump
author_rank: Frequent Contributor
timestamp: May 14, 2014, 12:56:26 pm
content: jpb you were right at 5v supply the output signal was too strong5v in = 2.53v out , freq registers on dvm but not on counter1.6v in = .83v out freq registers on counter as 1mhz exactly does not register on dvm(v measurements were taken on normal dvm on dc)can i use a vr to attenuate the signal ?david the counter is an optoelectronics 2810 handi countersorry cant find any specs on it to link

author: jpb
author_rank: Super Contributor
timestamp: May 14, 2014, 02:42:50 pm
content: Quote from: Flump on May 14, 2014, 12:56:26 pmI'd just use a resistor divider to attenuate as 1MHz is comparatively low. It depends on the impedance of your counter, mine has a choice between 1M and 50ohms. But assuming that your counter is high impedance you could just use something like 100 ohms in series with 50 ohms and with the counter across the 50 ohms so that the voltage is around one third.This will be much cheaper than say using a bnc attenuator.Of course, if your counter is 50 ohms then just using 100 ohms in series might do the trick.

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2014, 12:04:35 am
content: Quote from: jpb on May 14, 2014, 02:42:50 pmHow fortuitous that I have its big brother, the Optoelectronics 3000A. I like these counters but they are not substitutes for real test equipment. If you want a nice, basic, and inexpensive bench counter, I recommend a HP5314 (100 MHz 1 MOhm), HP5315 (100 MHz 1 MOhm), or HP5316 (100 MHz 1 MOhm, optional 1 GHz 50 Ohms, and GPIB). The HP5315 and HP5316 are also reciprocal counters which is nice for high resolution low frequency measurements.I ran some tests on the 50 ohm inputs on my 3000A and these counters are picky about signal level at the lower end of their frequency range so I am not surprised that you had problems. I think your 2810 lacks it but the high impedance mode on the 3000A works up to 50 MHz with fewer problems.

author: Flump
author_rank: Frequent Contributor
timestamp: May 15, 2014, 08:03:35 am
content: Thank you all for your input so farthis is all new to me and a steep learning curvebut i am taking in everything you have saidand i have learned quite a lot over the lastfew days about crystal oscillators and their accuracy.so the canned 1mhz oscillator i bought is +/-50ppmwhich over 1mhz means it could be +/- 50Khz which isquite a lot (only just learned what ppm is)so I need something more accurate and searched for what some of you sugested earlieran OCXO, 10Mhz was suggested so I found thishttp://www.ebay.co.uk/itm/251355497721?_trksid=p2055120.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITand I wonder what you guys thought about it as i know nothing about themwhat doesOutput Level : HC-MOS Compatiblemean ? does that equate to a voltage range ?Frequency Tolerance : +/- 0.15 ppm maxi think is +/- 1Hz is that right ?maybe i should have put this in the beginner section as i know so little about thisDave and jpbmy counter does have 50R and 1MR inputs, and a VR works to attenuate the signal on the 1MR inputstrangely my counter reads 001.000.018 but I dont know how accurate that is because of the +/- tolerance of the oscillator

author: ve7xen
author_rank: Super Contributor
timestamp: May 15, 2014, 08:44:33 am
content: Quote from: Flump on May 15, 2014, 08:03:35 amHCMOS is a standard logic family specification, the basis for 74HCxxx logic chips, and the specification means that it's compatible with this type of logic. It will have a square wave output with V(high) ~5V and V(low) ~0V when powered from 5V. Your counter probably (but by no means certainly) expects a sine wave input with 50R source impedance, which this is not. It might work anyway, read your counter manual if you plan to use it as a 10MHz reference and find out what the requirements are.PPM works just like % does, but instead of per-cent (hundred) it's per-million. So to work out 0.15% of 1MHz you would divide the % by 100 to get 0.0015 then multiply by 1MHz to get 1.5KHz. Likewise, for 0.15ppm you divide by 1e6 to get 0.15e-6 then multiply by 1MHz to reach an error of 0.15Hz. Or to put it more simply, if the error is max 50 parts per million, and 1MHz is a million parts (Hz), then your error can be 50 parts or 50Hz (not 50KHz). Makes sense?I am skeptical of the 0.15ppm tolerance claimed. The datasheet on the manufacturer's site doesn't mention absolute tolerance at all, and since this is a voltage controlled part with a pulling range of 4ppm +/- and aging of 0.5ppm in the first year, this tolerance seems to be very tight. Generally you would go to an OCXO for increased stability. Absolute accuracy requires a transfer standard, and a bare OCXO doesn't make a great one.

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2014, 05:12:52 pm
content: Quote from: Flump on May 15, 2014, 08:03:35 amYour 2810 counter may not be any more accurate than the oscillator; if it is like mine, then it is rated at +/- 1pmm over temperature and 1 ppm per year. There was a high stability TCXO option with double the accuracy but it was never clear to me how that was done since the frequency reference in mine looks like a normal XO.If you have a shortwave receiver, then you can beat your reference oscillator against one of the WWB signals to get into the 0.1 ppm range:

author: babysitter
author_rank: Frequent Contributor
timestamp: May 15, 2014, 06:32:32 pm
content: You can add a (diy) comb generator behind your reference source that gives you a lot of signals which relate as n times reference frequency. You want one.Broadcast stations usually hold their frequency very well, too, not just WW* and DCF77, and of course the mobile phone base stations that donate the Rubidiums which are all over the placeTo compare, a SDR dongle or so might help - there is a rtl calibration tool around.

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2014, 08:11:58 pm
content: The local broadcast solutions I have checked have been an order of magnitude worse than WWV even without accounting for propagation issues. Some analog TV stations used to phase lock their carriers to facilitate network transmission but that was a long time ago now.I suggested WWV because it will be more than accurate for calibrating a simple crystal based reference (0.1 ppm is feasible) and it is about the easiest and least expensive source to use.

author: jpb
author_rank: Super Contributor
timestamp: May 15, 2014, 08:43:34 pm
content: Quote from: David Hess on May 15, 2014, 08:11:58 pmWWV works well in the US but I think it isn't available in the UK. (I'm not an expert but that is my understanding.) Most radio synchronized sources here are based on either the 60kHz time standard broadcasts or the 198kHz BBC Radio 4 long wave broadcast but I don't think there are any neat broadcasts at 1MHz or 10MHz.

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2014, 01:47:11 am
content: I missed that you are in the UK. It should still work when propagation is good.There occasionally are inexpensive GPSDO kits which show up. Even the simple designs will be accurate enough for what you want to do.

author: SeanB
author_rank: Super Contributor
timestamp: May 16, 2014, 04:38:41 am
content: I can receive WWV or WWVH quite well here in South Africa at night, even with high levels of noise. Only way to tell them apart is to wait for the voice announcements.

author: babysitter
author_rank: Frequent Contributor
timestamp: May 16, 2014, 07:28:40 am
content: Have a look into the cheap SDR dongles again, they can calibrate against mobile phone base stations with a tool iirc called kalib-rtl.Multiplied output frequencies have the advantage that the error gets multiplied too.At least in germany the broadcasters take care of their carrier frequency, usually by disciplining to well-maintained rubidium.153 kHz Deutschlandfunk Donebach, which I visited once, gives you another radio station to compare against in the LF area that has the level of "frecuency standard dissemination". But dont trust it 5 minutes around 20:00 pm - they disappear to switch the radiation pattern then ! :-)

author: Flump
author_rank: Frequent Contributor
timestamp: May 17, 2014, 08:51:58 am
content: Quote from: ve7xen on May 15, 2014, 08:44:33 amI totally screwed up the math's on that one , I blame my calculator, the decimal point button is intermittentI cant get wwv from my qth at any time of the dayI have been looking at the data sheet for an OCXO but I cant workout what the accuracy (unpulled just standard) is,theres no ppm in the data.Iv'e attched the pdf incase anyone fancies a look and can decipher it lol

author: jpb
author_rank: Super Contributor
timestamp: May 17, 2014, 09:17:01 am
content: Does your counter go down to 1Hz (or measure period up to 1 second)?If so you can check your counter using a cheap GPS module with 1pps output.I found this one which I think originates from Adafruit though I got it from proto-pic :http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/It is a good module to have because it allows an external antenna and I've found that the jitter on the 1pps is less than 10nsecs which is pretty good.

author: Flump
author_rank: Frequent Contributor
timestamp: May 17, 2014, 09:57:45 am
content: hi jpb my counter has 2 inputs but neither of them go down that low,Input A - 50R , 1Mhz-3GhzInput B - 1MR, 10Hz-50Mhzthat looks like a nice module but I think it would be best if i get a 10Mhz OCXOso i can use it for other things as someone said earlier.thanks for the idea though

author: jpb
author_rank: Super Contributor
timestamp: May 17, 2014, 11:41:30 am
content: Quote from: Flump on May 17, 2014, 09:57:45 amI wasn't thinking of a replacement for the 10MHz OCXO but as a means of setting its frequency.The big advantage of GPS is it is an absolute standard (jitter aside) so that there are no worries about drift.There are modules that do higher than 1Hz but these tend to be snapped up by people building themselves GPSDO (at least the ones on e-bay) and ones like theUblox LEA-6T are expensive (just under £100 is the cheapest I can find).My counter (TTi 930) does 1 Hz (this was one of the reasons I chose it as I knew I wanted to design a GPSDO using 1pps) and by using my OCXO as a reference to the counter I can fiddle with the OCXO frequency until it reads exactly 1Hz for the GPS 1pps input (actually it works a bit better using the period measurement rather than frequency).Most counters seem to start at 10Hz or so - I found this when looking for mine where I was specifically looking to go down to 1Hz (of course the expensive Agilent ones go down to mHz but they are very expensive).It might be worth looking out for an old Motorola GPS module on e-bay with 100Hz output BUT be warned, these older modules like 5V antennas whilst most modern antennas are 3.3V and if you then start buying an antenna as well prices can mount (modern 3V puck antennas are only about £5).

author: G0HZU
author_rank: Super Contributor
timestamp: May 17, 2014, 01:29:57 pm
content: If you ask for a frequency standard recommendation on this forum you will get plenty of people telling you to go down the Rubidium or GPS route! Both options are a bit silly for hobby use and both options come with baggage because the GPS option means you ideally need to use an outdoor aerial to get it to work reliably, plus it can take 30 minutes to lock fully and the Rubidium standard is going to be expensive and power hungry and have a warmup time of many minutes as well. Plus you won't know if it is working reliably or how much useful life it has left as Rubidium oscillators have a finite lifetime.The thing to be wary of is that this forum has plenty of members where a significant part of their hobby activity revolves around playing with time standards and dc voltage standards where they try to achieve silly levels of accuracy. I haven't seen any evidence that they actually 'need' this accuracy in anything they are working on at home. I can only guess that they just like to have something 'accurate' to satisfy some inner need.The little MicroCrystal DIL14 OCXO is a fairly sensible choice as a fast warmup reference for a general purpose frequency counter for hobby use. I'd expect it will warmup in 30-60 seconds. You can expect it to age maybe a few Hz per year (away from 10MHz) if it is new. It will probably get better with age.The second OCXO you linked to (the 8663.pdf file) is a very high spec OCXO. This would be typical of an OCXO offered as a $$ factory option to fit to a lab grade signal generator or a decent frequency counter from one of the top test equipment manufacturers. i.e. it is going to be way better than the reference oscillator they fit as standard.It looks like it can achieve about +/-0.03ppm ageing over 1 year. So that would be about 0.3Hz ageing away from 10MHz (per year) after you initially calibrate it with its trimmer.I would expect that the 8663 OCXO would be quite expensive! It would also take quite a while to warm up and stabilise. Do you really need this level of performance? Maybe the faster warmup DIL14 OCXO would be the best compromise for hobby use even if it can only achieve 1ppm over a year.You still have to adjust it to initially calibrate it but this can be done by various means.

author: dannyf
author_rank: Super Contributor
timestamp: May 17, 2014, 01:55:43 pm
content: You can use a low frequency source (like the gps) to gate your oscillator to measure its frequency accuracy.

author: jpb
author_rank: Super Contributor
timestamp: May 17, 2014, 01:58:05 pm
content: Quote from: G0HZU on May 17, 2014, 01:29:57 pmI don't disagree with your comments, though I think anyone interested in science and electronics will tend to have Voltnut and Timenut tendencies. I'm building a GPSDO for fun and a learning experience but I certainly don't need the accuracy it should provide. But then your average 100m runner doesn't need to run as fast as possible over 100m, but it is fun to try and see how well you can do.My comments on this particular post were to try and answer your last point above rather than give super accuracy. If your equipment measures mHz (both my counter and the trigger frequency counter on my scope do) then the 1pps on a cheap GPS module does provide an accurate to at least 1ppb easy source that you can check in 30 seconds or so without the need of any calibration.This is very different from using a full blown GPSDO or Rubidium reference.The problem here is that the counter doesn't go below 10Hz (like many counters) so the approach won't work without more expense and complication.Dannyf's suggestion is a good one though it adds the complication of an and gate and flip-flop/latch perhaps.I think a cheap OCXO from e-bay is a good route but access to some means of measuring it is required as it may be out. But then if you're only requiring 1ppm accuracy it will probably be within that without adjustment.

author: dannyf
author_rank: Super Contributor
timestamp: May 17, 2014, 02:16:24 pm
content: QuoteIt probably isn't that difficult to put together an instrument that does just that, with binary read-out.QuoteI agree. Without it coming from a reputable manufacturer / distributor, you have no way of knowing how inaccurate it is.A tcxo is a better way to go in this case.

author: G0HZU
author_rank: Super Contributor
timestamp: May 17, 2014, 02:27:51 pm
content: In the original post the requirement was to calibrate the frequency function in a DMM and the timebase of a scope. Most DMMs will display 4 or 5 digits in this mode and I'd expect that the frequency reference inside the DMM will be pretty dire anyway. I'd be surprised if it was spec'd better than +/-100ppm.So even the little DIL14 OCXO is going to be more than adequate.This Microcrystal DIL14 OCXO is quite 'old tech' in that we used to fit a custom version of this little OCXO in some of our receiver products back in the 1990s. We had our own custom XV5 spec and I think we paid extra to get +/-0.1ppm over a wide temperature range and I think the warmup time ended up being longer than the usual 30seconds.I've got a few of them here salvaged from old dev boards and they do come in useful as a simple drop in upgrade to a std 10MHz DIL 14 oscillator or to any kit with a 10MHz reference oscillator. eg I've got one fitted to one of my Marconi 2019 signal generators after the std 10MHz oscillator failed on it. I've got another I use with an old Philips counter.If a few cheapo 74HC390 dividers were fitted then it would provide tap off points for 10MHz, 5MHz, 2MHz, 1MHz etc etc down to below 1kHz. So there would be outputs that would fall within the frequency range of the DMM and also the timebase ranges of the scope.

author: G0HZU
author_rank: Super Contributor
timestamp: May 18, 2014, 12:16:34 pm
content: I dug out a couple of Microcrystal DIL 14 10MHz OCXOs and tested them today. The versions I have here run from 12V and are to our XV5 custom spec and they warmup in about 20seconds to be within 1Hz. They take a couple of minutes to get within about 0.2Hz of the steady state condition. (takes 25mA from 12V in steady state)The total adjustment range is +/- 50Hz so even if you just set the trimmer at the mid point you would get within about 1 or 2ppm. So assuming the ones on ebay are genuine Microcrystal OCXOs then they are reasonably good value at £19.The only slight worry (if you wanted to get the best from it) is the sensitivity to the PSU voltage. I could get 1Hz drift for a 100mV change in supply voltage. The 10k trimmer resistor just acts as a pulldown resistor on one of the OCXO pins so this is isolated from the 12V supply.

author: yramgu
author_rank: Contributor
timestamp: May 18, 2014, 08:12:00 pm
content: An OCXO is indeed the best choice for this particular application.Then if you want porn-grade precision, and you're in the UK, you can try to catch a station like DCF77 (as previously proposed by Babysitter)^^DCF77 used an atomic clock producing a frequency of precisely 9 192 631 770 Hz, which is used to lock a 10MHz reference. From that reference, they produce a 77.5kHz carrier wave which is broadcast.You can use that 77.5kHz to lock your own 10MHz oscillator to produce a very stable reference. ON4JLV built one with a precision of 10-3ppm

author: babysitter
author_rank: Frequent Contributor
timestamp: June 12, 2014, 01:46:05 pm
content: Tell us how life is with a 10 MHz minus 10 Hz Oscillator when it has arrived ! O0

author: G0HZU
author_rank: Super Contributor
timestamp: June 12, 2014, 09:29:47 pm
content: QuoteI agree but on this forum 'best choice' always gets trumped by 'coolest most accurate' choice especially if if involves using test gear with lots of digits

author: Flump
author_rank: Frequent Contributor
timestamp: June 13, 2014, 01:32:11 am
content: Thanks again everyone for their input on this subjectbabysitter has been trimming a TCXO for me and it is currently on its way to me O0it needed trimming because I wanted a slightly under 10mhz reference,I will leave it to him to give any detail on it because he did all the testing.Quote from: G0HZU on May 17, 2014, 02:27:51 pmI would love this to be the next stage for my frequency standard is it easy to implement ?I have been googling frequency dividers but not found anything yet basic enough for meto try and build.

author: linux-works
author_rank: Super Contributor
timestamp: June 13, 2014, 02:08:44 am
content: http://www.leapsecond.com/pic/picdiv.htmI have some spare chips, so if you need one burned, I could probably help you out. or, just buy from the guy who wrote the code (probably better that way, since he deserves credit for his hard work).

author: babysitter
author_rank: Frequent Contributor
timestamp: June 13, 2014, 07:51:26 am
content: You should go the PICDIV Route definitely if you are interested in using it for gate times and other slow events.(Remember the Consider the 10 Hz error then!Another thing you might look into is buying some DDS Module from ebay and feed it from the TCXO; these would allow you to set a ratio and get a signal at your TCXOs Frequency times DDS ratio. Good to provide a test signal e.g. in the other ham bands.If you need a real 10 MHz Reference for this, feel free to trim a Oscillator exactly 10 Hz above the one you got from me. Easy with a ham radio sw rig and using soundcard + analyzer software or your counter.BRBabysitter

author: Flump
author_rank: Frequent Contributor
timestamp: June 24, 2014, 08:26:03 pm
content: Just wanted to update this incase someone else reads this hoping to findout how to do a 10:1 dividerthe 74LS90N which is easy to get hold of can do a 10-1 division and it tells you how to in the data sheet, at the top.and I wanted to show you what babysitter made for meits a tcxo which he adjusted to be 10hz under 10Mhzwhich I used to calibrate my frequency counter toThanks Hendrik

author: BalticLab
author_rank: Regular Contributor
timestamp: July 28, 2014, 09:24:00 pm
content: This is what I use:https://baltic-lab.com/2012/10/review-jackson-labs-gpstcxo-eval-board/Pretty affordable even for a home-lab!EDIT:QuoteFor a second I hoped you had bad grammar there and I was about to ask where I can hire that babysitter...

author: BalticLab
author_rank: Regular Contributor
timestamp: July 30, 2014, 04:05:03 pm
content: Sorry for double post but I just remembered that I have something laying around that fits very well in the topic: A brand new GPS disciplined Atomic Clock Standard. Atomic Clock for precision, GPS for accuracy (clock edge on UTC second).

author: grumpydoc
author_rank: Super Contributor
timestamp: July 30, 2014, 09:34:03 pm
content: Very nice - from whence and how much?

author: David Hess
author_rank: Super Contributor
timestamp: July 30, 2014, 09:56:24 pm
content: They are expensive and apparently they have had problem with the chip scale atomic clock modules:Affected Products: Jackson Labs or Symmetricom time/frequency reference boards based on Symmetricom chip scale atomic clock, most common unit is the CSAC GPSDO sold by both symmetricom vendors and direct from Jackson labsType of issue: Short and Long-term reliability, mfr couldn’t assure that if it works for 1week, 1month or 1year it is not an affected unitIssue: CSAC Loss of vacuum, sudden onset failure modeResult: CSAC unable to control the temperature, Indefinite warm-up state, ultimately the unit fails to reach a lock stateFailure Rate: Vendor noted ~5% of all units, internally it has been 1 of maybe a dozen or less units to dateResolution Status: Issue acknowledged by manufacturer but not resolved, still affecting all current stock and current production units, Jackson Labs will replace the CSAC part on the board and return without a fee though admittedly the new part may also failDetails:While resolving an issue with a Jackson Labs CSAC GPS Disciplined Oscillator board, we were made aware of a reliability issue affecting all timing boards built around the new Symmetricom Chip Scale Atomic Clocks (a.k.a. CSAC). There is a fundamental design flaw that can result in the loss of vacuum in the CSAC, which prevents the unit from being able to effectively control thepart’s operating temperature. The end result is a unit that is in an indefinite warm-up state. We were informed that all current and even currently produced units can fail in this way. The number we were given was ~5% of all units will fail, so we happened to get one of those 5%. The failure mode is a very sudden onset failure, for our case one day it worked and the next day (during a test of course) it did not. Also this is not a case of ‘if it works the first week then it will be fine’, it can fail anytime (in my case I had used it on a regular basis for several months prior to the failure). Our unit also spent 99% of its life in an air conditioned lab so certainly not subjected to even a remotely harsh environment.

author: G0HZU
author_rank: Super Contributor
timestamp: July 30, 2014, 10:50:08 pm
content: The original requirement was to calibrate a 100ppm DMM or a scope timebase!A cheap OCXO is all that is needed.However, if anyone in the UK wants a novel quick and dirty 'standard' that is (kind of) traceable in the UK you could make a little 198kHz trf receiver from junk parts and run it into a (very) hard limiter and measure the frequency of Radio 4 when averaged over a few seconds with a reciprocal counter. I used an active trf stage ahead of the limiter section of a salvaged Philips NE604/SA604 FM IF/DET chip.I just tried this and could reliably get 198.000001kHz on an old Philips reciprocal counter (run from a decent external reference) with a 10s measurement time. I've shown a 1 at the end of the 198.000001kHz but sometimes it shows a zero here or flicks down 1 LSD. If I watch it over several minutes there is the odd rogue count that jumps up about 5-10 LSDs but most counts are as good as the digits I posted above. It will probably work more reliably during daylight hours.It 'works' within a few seconds (as opposed to 30-60minutes for a big OCXO or GPS) and runs on flea power.I bet there's hardly anybody on this forum that 'needs' anything better than this for home use.About 20yrs ago I designed a cheap and cheerful offair standard that locked a 10MHz reference to the 198kHz signal from R4. It's built in dead bug style and is (now) fitted inside an old plastic ice cream tub. It works a bit better than the crude trf receiver but I'm not sure I really need the extra performance. I never ever bothered making a neat version beyond the ugly prototype because it only got used a couple of times a year at most.

author: G0HZU
author_rank: Super Contributor
timestamp: July 30, 2014, 11:35:03 pm
content: I tried it with my other reciprocal counter and set it to a 1 second gate time. This counter didn't cope as well with the jittery output from the limiter so I tried averaging the readings over a few minutes.Obviously, it jumps around like crazy like this for each 1 second reading because the limiter can't remove all the modulation but I logged the counter and averaged the readings with a PC and was able to get a 198.000000kHz average within 200 counts.Obviously, not everybody has access to a reciprocal counter and some counters might not cope as well as mine have. But it is certainly a cheap and cheerful option for people in the UK.For anyone who doesn't know about BBC Radio 4 in the UK the 198kHz transmission frequency from Droitwich is locked to a very accurate time standard. So this adds some traceability to the cheapo trf receiver + limiter approach.

author: Andy Watson
author_rank: Super Contributor
timestamp: July 30, 2014, 11:41:42 pm
content: Quote from: G0HZU on July 30, 2014, 10:50:08 pmWhat a coincidence! I was looking at Radio 4's time keeping abilities earlier today. It's not so dirty if you can lock to it, and once-upon-a-time it used to be traceable to the NPL standards.http://tinyurl.com/lzurwkmLooks like NPL stop monitoring frequency and time in 2012. The BBC now say that the Radio 4 frequency is locked to a rubidium frequency standard.What I was actually trying to find out was whether Radio 4 longwave is still phase modulated with time signals.

author: BalticLab
author_rank: Regular Contributor
timestamp: July 31, 2014, 04:42:09 pm
content: Quote from: David Hess on July 30, 2014, 09:56:24 pmExpensive is relative to what you are doing. Just because you can get cheap burnt out rubidium standard from eBay for $ 100, you shouldn't distort the fact that they once cost just as much as the CSACs. If I remember correctly, Jackson labs responded and said they will replace Units affected by the issue free of charge even if they're out of their normal warranty time already.

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2014, 05:16:53 pm
content: Quote from: KF5OBS on July 31, 2014, 04:42:09 pmWell, I meant expensive in the sense of "if you have to ask, then you cannot afford it".I made some effort to find prices but stopped when I found that their comparable GPSDOs are in the $1000+ range. One of their low end units can be had for like $400 or so.A GPS disciplined crystal oscillator will be a lot more economical if you can live with its limitations.QuoteThey did which I have to give them credit for and they were not the only ones affected by the Symmetricom CSAC issue.

author: bingo600
author_rank: Super Contributor
timestamp: July 31, 2014, 08:44:34 pm
content: Quote from: KF5OBS on July 31, 2014, 04:42:09 pmIt does say eval sample on the CSAC , does that mean you got one from Said for free ?Then expensive is really relative/Bingo

author: BalticLab
author_rank: Regular Contributor
timestamp: July 31, 2014, 09:49:30 pm
content: QuoteI haven't paid for 99 % of the things on my blog. That does include the CSAC. The CSAC was a real challenge for Said because the CSAC itself is not Said's product. It's the GPSDO part. The CSAC is the biggest cost factor though. So he approached Symmetricom, got a free CSAC and then modified one of their PCBs and the SW to make it work with the "off standard" 10.24 MHz frequency. Thought that was pretty nice and impressive to do that just because.However, I think they sell for around $ 1500 now. And like I said earlier, a good nuclear standard is definitely worth that. I'm sure the rubidium standards all over the place from eBay used to cost a similar chunk of money back when they were new and had acceptable phase noise. Usually, if you need that amount of precision, odds are that you have the cash.