Recommend me an OCXO. - Page 1
Forum section: electronics / projects

author: Vgkid
author_rank: Super Contributor
timestamp: March 26, 2015, 12:45:04 am
content: I will finally start building my gpsdo(Brooks Shera design).starting off, I'am fairly open with my design constraints, but they are as followed:price under $150.00, though if slightly more expensive then that is ok.(Ebay prices)max height is 3.5in (88mm), though I can mount the ocxo sideways, if it is meant for itFrequency: 5/10 MHZ. I can work with other easily multiplied/divided frequencies, though they seem to be not as common12/24 volts, seem to be common.start your suggestions.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 26, 2015, 02:40:46 am
content: What do you want to use your GPSDO for? If it's just a 10 MHz frequency reference, you can use almost any OCXO. If you want to use it as a master oscillator to multiply up to 10 GHz, you need to focus on an OCXO that has better than average phase noise.Ed

author: Vgkid
author_rank: Super Contributor
timestamp: March 26, 2015, 04:19:53 am
content: It will be used as a frequency reference.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 26, 2015, 05:59:20 am
content: If you go for ebay, consider Morion MV85, MV89 series, "Trimble" labelled ones, C-MAC or MTI. Reasonable cheap but as with all ebay OCXOs, you can be lucky and get a stellar performing device, a average unit, one that needs repair or something that belongs to a landfill.The price of HP 10811 and relatives is hyped up and you can get units in the same performance classes.What problems with a OCXO would you like to escape, and how would you see the interference?

author: awallin
author_rank: Frequent Contributor
timestamp: March 26, 2015, 06:38:00 am
content: From this graph of a free running Rb-clock and a GPS-disciplined Rb clock it seems you'd really want something that is stable out to 1e4 or 1e5 seconds that can then be locked to the relatively noisy GPS 1PPS:http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gifdoes anyone know of similar graphs for OCXO-based GPSDO's ? Depending on the OCXO the free-running ADEV starts rising already at 1s, or for the best OCXOs maybe after 100s. Anyway it seems there will be a rise in ADEV ('bump') before the disciplining takes effect and we move down again along the GPS curve.Does DIY triple- or quadruple-ovenizing an OCXO help? At least make sure the input voltage and tuning voltage are very stable.KO4BB has a comparison spreadsheet here:http://www.ko4bb.com/manuals/download.php?file=02_GPS_Timing/OCXO_Characteristics.xlslet us know how you make progress!AW

author: dannyf
author_rank: Super Contributor
timestamp: March 26, 2015, 09:16:30 am
content: QuoteI looked at that design and I would say that it is fairly dated and overly complex.I just finished, in a separate thread, a local oscillator disciplined by a 1pps signal. In my case, the phase detector was built around a pic16f684 + a low pass filter. The output signal is used to discipline a 1pps generator built around your desired oscillator. When integrated, the two does a good job getting to a robust synchronization.All built around two pic16f684, one VCTCXO and some passive parts, on a breadboard, for less than $5 in parts cost - excluding the oscillator. If you feed the phase detector with a reference 1pps signal from a gps, you get yourself an inexpensive GPSDO.

author: bingo600
author_rank: Super Contributor
timestamp: March 26, 2015, 02:40:37 pm
content: Quote from: blueskull on March 26, 2015, 09:28:39 amWhat software version is the X72 ?AFAIK it has to be >= 5.xx for the 1PPS diciplining to work on a X72.1-PPS diciplining certainly is non existant on my 4.xx version of the X72.I think you could get a PRS10 for around $400 on *bay , witch has the 1-PPS diciplining./Bingo

author: Vgkid
author_rank: Super Contributor
timestamp: March 26, 2015, 06:44:22 pm
content: The rubidium options PR10 are mighty tempting. I'm sort of taking this as an exercise, of run an ebay osc. Or trust in the spec of my own ebay crystal ocxo's. Reading through the modern rakons I noticed that the specs do change based on the package size, for the same series.CFP04-A1, package 40, 40x30x20

author: jpb
author_rank: Super Contributor
timestamp: March 26, 2015, 08:40:48 pm
content: I too am building a (or several) GPSDO (s) as they present an interesting challenge.I would read through the various Time Nuts archives. There is quite a good discussion of the Brooks Shera design.If you can get a GPS with 10kHz output then the James Miller design is very straight forward and you can buy a board off him.http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htmAs to OCXOs the one that is the gold standard is the HP10811 but these are pretty expensive, I've been bidding on a few and the cheapest go for $70 to $90 (I just missed one at $70). A good Morion MV89 is good but there are also a lot of duff ones around. Similarly, the MTI 260 series is very good though a lot of the ones on e-bay are non standard so the specs are unknown.In fact that is the trouble with OCXOs off ebay, you need to buy several and check them, but this gets expensive.The leapsecond web site and several others are worth reviewing as well.http://leapsecond.com/The whole thing can get quite addictive!

author: KJDS
author_rank: Super Contributor
timestamp: March 26, 2015, 09:06:56 pm
content: I've got an assortment of HP units kicking around for parts. I'll have a rummage through and see what OCXOs are in there.

author: dannyf
author_rank: Super Contributor
timestamp: March 26, 2015, 10:21:14 pm
content: QuoteWhat about just buying from a distributor (digikey for example)?Or diy?

author: Vgkid
author_rank: Super Contributor
timestamp: March 26, 2015, 10:50:51 pm
content: The thing with new ocxo's is that they are relatively affordable as lower specced units, but as you slowly increase the performance, the price grows exponentially.

author: jpb
author_rank: Super Contributor
timestamp: March 27, 2015, 11:51:44 pm
content: Quote from: Vgkid on March 26, 2015, 10:50:51 pmYou're right, but you can get good new ones for about 2-5 times the second hand ebay price which, given that the new ones are much less power hungry and are smaller might be worth it.I've bought one new one for £128+VAT = £154 but I got it on a 2 for 1 offer at Farnell so the price was actually around £80.http://uk.farnell.com/iqd-frequency-products/lfocxo063815/oscillator-ocxo-10mhz-thd/dp/2443060The ebay ones I've bought have typically been around £30 to £40 by the time I've paid postage and import duty, though I did get a couple for around £10 but to get a HP10811 would probably be nearer £80+ by the time I've paid postage and import duty etc.At least 2 of my e-bay ones have been dead on arrival, though I got a refund for one and a replacement for the other it all represents hassle. And even if they do work they are often starting to go towards the end of their tuning range.The advantage of the new one is that it is 3.3V instead of 12V and very small and neat, though I've not properly tested any of them for Alan Deviation (I don't have a Hydrogen Maser so I'll need to test each against each and haven't had time to do so yet).The high end OCXOs bought new are very expensive.For example, a Wenzel Associates Premium 5 MHz-SC Blue Top Ultra LOw Noise Osc is £4,715+VAT !even more expensive is the Oscilloquartz 8607-BM which is a BVA one :http://www.oscilloquartz.com/files/1363164953-Br_%20OCXO%208607.pdfThis costs 34,040 Swiss Franks + VAT (which is around £28,000 inc VAT!!!!!)

author: Vgkid
author_rank: Super Contributor
timestamp: March 29, 2015, 05:12:24 am
content: I have narrowed it down to a few contenders:C-mac :CFP-04A1, my unit.STP2145AI wish more of the stp units had datasheets, seems to denote custom ones :/drift specs the same as mine(I think/hope), but 20x better tempcoMTI:MTI-260-624, plentiful on ebay.HP:10811-1065, was used in the early Z-boxes, 10811-60160 internal to the ovens.sum had bad ovens(10811-60160), needs 24v, priceyOsciloquartz:8663----------power wise i've decided 12v is preferred.Any other options.

author: jpb
author_rank: Super Contributor
timestamp: March 29, 2015, 01:04:46 pm
content: It might also be worth considering the Isotemp 134-10, I just got a very clean one off ebay which shows no signs of being used (though I guess it must have been, it hasn't been soldered) and my preliminary tests show it working well. It also has a oven monitor pin that on my unit goes from 8mV (i.e. 0) up to just over 5V when the oven is up to temperature.They also have a handy mounting bracket.The one I got was only around £16 + £9 postage.It is the one that James Miller used in his earlier GPSDOs with good results though it is not in the same class as say the HP10811.There were several on flea bay until very recently but I did a search just now and they seem to have disappeared.One thing about the MTI 260-624 is it was a special (it is not a standard number) so it is difficult to know what its specs are but I don't suppose this matters much as I guess specs change over twenty years or so anyway.

author: elmohandis
author_rank: Contributor
timestamp: April 05, 2015, 01:37:55 am
content: Checkhttp://magicxtal.comout.

author: Vgkid
author_rank: Super Contributor
timestamp: April 05, 2015, 04:02:07 am
content: I grabbed a stp2145a from taobao.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: April 06, 2015, 10:32:12 am
content: You've the Axtal Axiom 40 use in the latest GPSDO by James Millerhttp://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htmor in the New Generation Beacons by OZ2Mhttp://www.rudius.net/oz2m/ngnb/gps.htm.But haven't seen any schematic with the Axiom 40 or others.Or this one with MV89ahttp://pe9ghz.org/cmsms/index.php?page=gpsd

author: SteveyG
author_rank: Unknown
timestamp: April 06, 2015, 02:53:00 pm
content: The Morion MV89As are really good and go for reasonable prices on eBay. I bought the middle one in the photo here:http://www.ebay.co.uk/itm/161600479345https://twitter.com/sdgelectronics/status/585092081116413954It arrived in a week to the UK. It may get used in my GPSDO that I tore down in my YT video.

author: jpb
author_rank: Super Contributor
timestamp: April 06, 2015, 02:57:00 pm
content: Quote from: SteveyG on April 06, 2015, 02:53:00 pmYou can get good MV89As, I have one that seems good, but there are a lot around and some are not good - I've had at least one duff one.I just received an MTI261 which should be good and it sort of works, but the wave form is in very odd shape unless the voltage is kept very low (below the specced value) in which case the frequency is a bit out (that is it can't be tuned to 5MHz). I can't say it doesn't work but it is certainly not as it should be but I'm not sure I can go through the hassle of returning it to the US.

author: SteveyG
author_rank: Unknown
timestamp: April 06, 2015, 03:01:18 pm
content: I had one Trimble OCXO that I couldn't trim below 10000004Hz, the seller just sent me another after sending a photo of how I had it set up with the frequency counter. eBay is pretty safe these days for buyers.

author: edavid
author_rank: Super Contributor
timestamp: April 06, 2015, 03:35:31 pm
content: Is it true that the MV89A is a 5MHz oscillator with a doubler? (I think I read that on time-nuts, but I can't find the posting now.)

author: jpb
author_rank: Super Contributor
timestamp: April 06, 2015, 07:28:22 pm
content: Quote from: edavid on April 06, 2015, 03:35:31 pmI also read that on time nuts - it was a comment about how the variation in wavelength (jitter I guess) is around a nsec and this upsets time nuts.

author: KJDS
author_rank: Super Contributor
timestamp: April 07, 2015, 10:03:42 am
content: I've got a pile of Racal-dana 9500 series counters that have too many problems with them to be worth fixing. I've taken the lid of the first one and the OCXO is labelled M95XCPO.Does anyone have any info on these and is anyone interested? offers welcome, will make sure they work before shipping

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: April 07, 2015, 11:49:31 am
content: KJDS,I can't find any data for the M95XCPO, so it could be an custom part made for the Racal-dana.

author: Vgkid
author_rank: Super Contributor
timestamp: April 07, 2015, 08:45:31 pm
content: Ironically that Racal 9500 was the first Frequency counter I was looking at getting. Ordered one on Ebay, and got a message from the seller the next day, saying that his shop was broken into. So no 9500 for me, ended up getting a 5335A. Now I'm contemplating getting a prologix gpib(used), already downloaded ezgpib/timeLab.It has begun...

author: Vgkid
author_rank: Super Contributor
timestamp: April 22, 2015, 04:55:40 am
content: my stp2145A 's came today, along with a neat little gps board.

author: Vgkid
author_rank: Super Contributor
timestamp: April 22, 2015, 10:24:26 pm
content: The board works, now to wait until summer to start the project.currently running a non scientific test using the 3456A monitoring the stability of the EFC output voltage.will update later:temp span 22.5+/- 1.5Clow = 8.01727 Hi = 8.01734 mean = 8.01730 var = =.170525E-9count = 6411 measurements, 100nplc, 6 digits

author: bingo600
author_rank: Super Contributor
timestamp: April 24, 2015, 02:21:35 pm
content: Quote from: Vgkid on April 07, 2015, 08:45:31 pmPoor sodBeing bitten by the time bug is EXPENSIVEMy infection started with "just wanting to cal" my old PM6674 counter.Ended up with 3 x Tbolts , 5 x RubidiumsYou have been warned/BingoAnd now i've been bitten by the volt bug

author: feedback.loop
author_rank: Frequent Contributor
timestamp: April 29, 2015, 12:04:37 am
content: You may want to check out this video:https://youtu.be/0UT6smae8M0Two OCXOs are tested there:1. Morion MV85a 5V sine wave2. C-MAC 12V square wave

author: Vgkid
author_rank: Super Contributor
timestamp: April 29, 2015, 02:40:41 am
content: Thanks for the video. If you dont mind me asking, where are you from?I think i might have most beat on number of ocxo's. 54

author: Vgkid
author_rank: Super Contributor
timestamp: April 30, 2015, 05:14:36 am
content: Measured the current draw at 21C for the stp2145Ainit = 546mA, min = 147mA, avg = 178mA

author: xrunner
author_rank: Super Contributor
timestamp: April 30, 2015, 01:41:22 pm
content: 100 MHz OCXO - Valpey Fisher. Form Ebay for $40. Now I have a 10MHz and a 100 MHz. Must obtain more ...

author: Vgkid
author_rank: Super Contributor
timestamp: April 30, 2015, 11:11:21 pm
content: I almost thought about picking up a 100MHZ ocxo. Currently logging the evc out on one of the 2145A's. Which is being fed by a rather precise(and stable) 10v source(as opposed to 12v). will update later.

author: Hole
author_rank: Contributor
timestamp: August 02, 2016, 11:07:16 am
content: I know its old, but just to add some details.I got a racal 9500 series counter and here is what I found inside. Name seems to be M95OSEO or M950SE0.Previouse owner marked "option 22a installed" in the manual, which says "Aging rate: < 3x10^-9/day, Temperatur stability: < 3x10^-97°C 0° C to +50° C, Voltage Stability: <2x10^-8 with 10% line V variation".It looks like C5 had to suffer some abuse. Not sure what all the stuff does... Currently the counter is very very spot on.

author: Vgkid
author_rank: Super Contributor
timestamp: August 02, 2016, 05:40:18 pm
content: C5 might be a decoupling capacitor.

author: Hole
author_rank: Contributor
timestamp: August 02, 2016, 06:09:27 pm
content: Yes, all the lighter colored ones seem to be decoupling. And it totally looks like a later made hack.Another mystery is channel C. It is available as option 41 (50 to 512 Mhz) and option 42 (50 to 1.25 GHz). I can't find out what is build in, I don't see any markers etc.Perhaps I should draw a schematic...[times passes...]ocxo is a Frequency Std. 9442/5, 5 MHz fast warm up. And I assume that the pcb is some frequency doubler (OR + RC).