Best overall GPSDO for <200 USD? - Page 1
Forum section: electronics / testgear

author: rfspezi
author_rank: Regular Contributor
timestamp: April 03, 2018, 01:43:09 pm
content: In the past days, i have read through several GPSDO topics on the net - however i am more and more unsecure which device is the best choice in overall performance for <200 USD.I would be happy if some experienced GPSDO users could help me decide which one to choose as 10 MHz reference for a spectrum analyzer and frequency counter.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: April 03, 2018, 03:01:31 pm
content: PossiblyeBay auction: #181948031179

author: wolfp
author_rank: Contributor
timestamp: April 03, 2018, 05:08:51 pm
content: I use the GPSDO of Leo Bodnar as reference for my 10digit frequency counter and for calibrating my receivers. It makes sense to have an outdoor GPS-antenna on the roof with free sight to the sky. The GPSDO of Leo has 2 outputs. There is also a version which is cheaper and has only 1 output. The output-frequency is programmable so you are not fixed to 10 MHz.

author: nctnico
author_rank: Super Contributor
timestamp: April 03, 2018, 06:04:17 pm
content: First you have to ask yourself if you really need a frequency reference. If the spectrum analyser and frequency counter have a 10MHz output then you can synchronise them together or use them as a reference for the circuit to be tested.I have a BG7TBL GPSDO and it works well (for the project I'm using it for I also need a 1PPS signal). Putting the antenna under a wooden roof is good enough. The control loop will filter out most of the junk anyway.

author: rfspezi
author_rank: Regular Contributor
timestamp: April 03, 2018, 08:09:33 pm
content: Quote from: wolfp on April 03, 2018, 05:08:51 pmI fear this one is no option since it only got a TCXO for a price no much below the OCXO equiped ones.From what i read so far, i thought the Trimble based GPSDOs are the best ones?

author: NivagSwerdna
author_rank: Super Contributor
timestamp: April 03, 2018, 08:28:35 pm
content: Quote from: rfspezi on April 03, 2018, 08:09:33 pmKeep reading.If I was buying another one I would probably go foreBay auction: #122813436461which is the most modern of the ex-cell tower GPSDOs I have seen. It's very nice but obviously you need to be interested enough to interface to it.

author: texaspyro
author_rank: Super Contributor
timestamp: April 04, 2018, 04:10:34 am
content: Quote from: NivagSwerdna on April 03, 2018, 08:28:35 pmThat one is a pain to connect to and use (but Lady Heather supports it).This one is rather nice, tested out better than the Trimble/Symmetricom telecom units. The OCXO on it is VERY nice... it is Oscilloquartz's highest spec version of the 8663.https://www.ebay.com/itm/10Mhz-GPSDO-OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock/262861459973?hash=item3d33c39205:g:sbYAAOSwh2xYAjrpThere are also some Trimble Thunderbolts listed for under $200. The oscillators on the gold boxed Thunderbolts are known for their excellent phase noise.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: April 04, 2018, 10:42:27 am
content: Quote from: texaspyro on April 04, 2018, 04:10:34 am+1

author: rfspezi
author_rank: Regular Contributor
timestamp: April 04, 2018, 11:54:28 am
content: Quote from: texaspyro on April 04, 2018, 04:10:34 amThe more i read, the more i loose trust in any GPSDO.There are warnings that the used OCXOs are likely to be at the end of their lifespan in terms of frequency-trimming voltage range.So they might soon not be trimmable to 10.000 000 MHz anymore?

author: NivagSwerdna
author_rank: Super Contributor
timestamp: April 04, 2018, 12:20:31 pm
content: Quote from: rfspezi on April 04, 2018, 11:54:28 amThe ex-cell tower GPSDOs were originally expen$ive, they may have been damaged when they were reclaimed, they might have untrim-able OCXOs, they may be covered in oily slime... They are cheap for the technology you get.You could always get a Rubidium Standard...eBay auction: #112567697403which has the advantage that you don't need to leave it on for long periods of time.or you could put a decent TXCO or OCXO in your counteror you could get nothing.

author: jpb
author_rank: Super Contributor
timestamp: April 04, 2018, 02:10:22 pm
content: Quote from: rfspezi on April 04, 2018, 11:54:28 amThis is a risk, I've just bought one off e-bay as I think there are ways to mitigate the risk. First, I can measure the control voltage to see where it settles within the return period (though the cost of shipping it back to China may be prohibitive) - if it really is at an extreme value I think the seller would probably replace it.Secondly, I've acquired quite a few new old stock OCXOs off ebay over the years so in future it may well be possible to replace the OCXO though this may require some sort of daughter board.Also, the life span of around 10 to 20 years for OCXOs is based on worst case, drift generally decreases with age and with good fortune it may be fairly stable well within range.If you're really worried then get something like Leo Bodnar's one which uses a new device so won't have aging issues but of course the device is just a TCXO and won't have the same stability as a double-oven OCXO.The datasheet on the 8863 OCXO has aging at 10^-8 per year with tuning at +/- 0.3 ppm so 0.3*10^-6/10^-8 gives a tuning life of 30 years - the drift on the lower option model is 1.5 *10^-8 so this would be 20 years.The Lea 5T GPS module was launched on the 2nd April 2008 :http://www.insidegnss.com/node/600So these GPSDO cannot be more than 10 years old so by my calculation they should have 10 to 20 years of life left in them.These modules have been superseded, perhaps by rubidium units or other means I don't think they have, by any means, reached the end of life.I've just also checked on the data sheet for the GPSDO itself and this is dated Nov 08, there may have been revisions but it all points to an age of less than 10 years for something with a life of potentially double that.

author: texaspyro
author_rank: Super Contributor
timestamp: April 05, 2018, 06:31:35 am
content: I don't worry about OCXOs "aging out". Once most OCXOs reach a couple of years old their aging tends to settle down to rather low values. I have over 50 GPSDOs, some over 30 years old, and none are close to their EFC limits. I have a 30 year old HP unit that has an EFC sitting at +6% of nominal. On a Thunderbolt that was well used when I got it and has been running here for over 10 years, the EFC voltage has changed less than 150 mV since I got it. YMMV...

author: Dwaine
author_rank: Frequent Contributor
timestamp: April 05, 2018, 10:46:31 am
content: https://www.ebay.com/itm/10Mhz-GPSDO-OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock/262861459973?hash=item3d33c39205:g:sbYAAOSwh2xYAjrpThat’s the device which I bought. It’s been great and there has been no problems with it. I did the management mod as you suggested. It’s been running great.

author: Cerebus
author_rank: Super Contributor
timestamp: April 05, 2018, 01:03:41 pm
content: I know that anecdote is not the singular of data, but my recent experiences might be of interest.I recently picked up one of the many ex-equipment OCXOs from one of the usual Chinese sources. It's an ISOTemp 143-141 that shows signs of having seen better days. It's been desoldered fromsomethingand most of these that pop up on the market seem to be 10 years or so old. This one has a date code from 2010 so is a little younger than some.It's been sitting powered up since the 25th (12 days) being watched by a frequency counter that's GPS locked. It started off 118 ppb high and after a few days retrace settled down to 143 ppb high and has sat there or very close to there since the 29th. This oscillator has a pull range of +/- 400 ppb and so its current performance is still well within the range where it can be pulled to its nominal frequency.This is only one example, but it lends a little confidence to the idea that these parts, although quite old, still have a useful working life left in them. Don't forget that the age related drift of crystals tends to follow a square root law, drifting more and more slowly as time passes.

author: jgalak
author_rank: Regular Contributor
timestamp: April 08, 2018, 01:26:28 pm
content: When looking at GPSDOs to use as 10MHz reference standards, what are the figures of merit one should consider? Freq stability is obviously one, but are there other things? Some sort of jitter measurements? Phase noise? Something else?

author: aronake
author_rank: Frequent Contributor
timestamp: March 25, 2022, 07:18:47 pm
content: A bit of an old thread, but I have same questions, which below 200 USD GPSDO do people recommend? I would also think there has been some development in this area.

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2022, 07:33:25 pm
content: No one has posted a link to GPSDO's at Leo's shop:http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107Suitable antennas here:http://www.leobodnar.com/shop/index.php?main_page=index&cPath=122

author: J-R
author_rank: Super Contributor
timestamp: March 25, 2022, 08:03:24 pm
content: I recently picked up Leo's dual-channel GPSDO and also an HP 5334B. Was happy to see they agreed to within 0.03Hz at 10MHz.The included GPS antenna worked just fine for me indoors.You get firmware updates and a basic utility program and support is responsive.Selecting different frequencies on the dual-output version can be a little bit of extra work, so if you need that regularly, they suggest two of the single units and I agree.I found the output voltage of Leo's GPSDO to be a little low for some of my equipment, so I'm experimenting with some distribution amplifiers.Using the output from a function gen locked to the GPSDO can be a good solution for those issues, though.