transferfrequency standard - Page 1
Forum section: electronics / general

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 22, 2013, 03:44:46 am
content: like the Geller voltage standard, are there any cheap frequency transfer standards for hobbyists other than trying to make those big power hungry rubidiums on eBay work.I believe the Chinese have found the solution.http://www.ebay.com/itm/1KHz-33MHz-Adjustable-Oscillator-Module-LTC1799-/400292172818?_trksid=p2045573.m2102&_trkparms=aid%3D555001%26algo%3DPW.CURRENT%26ao%3D1%26asc%3D146%26meid%3D7133796153751738922%26pid%3D100034%26prg%3D1079%26rk%3D1%26sd%3D190820631639%26data sheet:http://cds.linear.com/docs/Datasheet/1799fc.pdf

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2013, 07:51:08 am
content: Quote from: peterthenovice on April 22, 2013, 03:44:46 amAn OCXO will be pretty good - plenty cheap on ebay and should get below 1PPM.QuoteThat's not a frequency standard - way less accurate than a simple xtal oscillator.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 22, 2013, 08:08:04 am
content: There are quite a few GPS locked sources on eBay----Hams use them for very narrowband digital comms down in the noise.They require a pretty good level of stability.OK,stability & absolute accuracy aren't necessarily the same,but if you are looking for a very low level signal ,it's nice if both ends of the system are "on the same page".

author: codeboy2k
author_rank: Super Contributor
timestamp: April 22, 2013, 08:11:32 am
content: Quote from: mikeselectricstuff on April 22, 2013, 07:51:08 amI bought an OCXO off ebay. I only have a 10 digit counter, it powered up and read 10.00000001Mhz, with the last 1's digit flickering on and off, so it's at least 10ppm. I can't see the 1Hz digit, and my counter uses a standard crystal, not an oven, so my counter might even be off a little. But the OCXO is pretty good for me.I plan to discipline it to a GPS receiver. That should get it even better.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 22, 2013, 08:30:13 am
content: Quote from: peterthenovice on April 22, 2013, 03:44:46 amHello,the SI-unit "Time" has the big advantage, that it comes through the air, and free of charge.The chinese solution is really bad for that purpose.Used OCXO may be ok, if calibrated before, then they may have an uncertainty of 10e-9, short term stability even higher.Much easier is to buy a GPS based standard, as the famous Trimble Thunderbolt.Properly set up, you get an uncertainty of 10E-10 in one second, and 10E-12 or better in one day.That's nearly the level of an Cs atomic clock!Or you may use your local long or short wave radio stations for Time distribution, in US, that's WWVB or WWV.There are complete receiver sets available, too.Frank

author: amyk
author_rank: Super Contributor
timestamp: April 22, 2013, 10:52:43 am
content: Thetrimpots on that boardprobably contribute more accuracy drift than the chip itself.

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 22, 2013, 11:52:49 am
content: I was looking for a small light weight solution that you can send get it calibrated very cheaply through the mail. the Geller is a 6 months accurate device. I was think about running a 5v oxco with a 9v battery.

author: ecat
author_rank: Frequent Contributor
timestamp: April 22, 2013, 12:06:09 pm
content: Quote from: mikeselectricstuff on April 22, 2013, 07:51:08 amAny opinions on these Heath-Robinson implementations?http://www.romanblack.com/xoven.htmhttp://www.qsl.net/m0ayf/Crystal-Ovens.html

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 22, 2013, 05:06:19 pm
content: Quote from: peterthenovice on April 22, 2013, 11:52:49 amYou may buy a TCXO, for a few bucks, normally those are calibrated already to ~1ppm, and are relatively temperature stable. Much better than the chinese toys, and obviously sufficient for beginning.OCXO on battery? Makes no sense. You'll need a decent PSU, 12 or 24V, depending on the OCXO. If calibrated, they take several days until they stabilize back to their initial value. Afterwards, let it run indefinitely.Frank

author: ve7xen
author_rank: Super Contributor
timestamp: April 22, 2013, 07:12:17 pm
content: Quote from: ecat on April 22, 2013, 12:06:09 pmI think the problem with these is that the only cheap and readily available crystals are AT-cut, which has a turn point close to room temperature. If you want it to be immune to room temperature fluctuations you need some headroom above room temp in your heater, but that puts you away from where the turning point of the temperature vs. frequency curve is, making it more sensitive to temperature fluctuations. Also SC-cut are much flatter around the turning point than AT-cut.GPS is a cheap and extremely accurate time / frequency standard. It also has the benefit of long term (weeks -> years) stability better than anything anyone can do on their own, since any error / long term drift is tuned out of the system by USNO. There's not much reason to use anything else unless you're a national standards lab or don't trust the US government to be distributing accurate time.

author: Unknown
author_rank: Unknown
timestamp: April 22, 2013, 09:28:18 pm
content: A frequency standard most used is the low or high frequency clocks like WWV USA, or in UK similar time signal; or our BBC radio 4 transmitter; in this regard see the below URL for a UK company, who sell a kit for radio 4...http://www.spectrumcomms.co.uk/Test.htm

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 24, 2013, 04:07:01 am
content: Quote from: vlf3 on April 22, 2013, 09:28:18 pma 10 MHz lab standard not a radio standard.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 24, 2013, 05:26:56 am
content: Quote from: ve7xen on April 22, 2013, 07:12:17 pmWhat about a Peltier heat pump? One sized to heat or cool a crystal oscillator module can be quite tiny.

author: EEVblog
author_rank: Unknown
timestamp: April 24, 2013, 09:47:54 am
content: Quote from: peterthenovice on April 22, 2013, 11:52:49 amYou won't run any ovenised oscillator off a 9V battery.The closest self contained solution would be a DTCXO of some sort.This solution from Symetricon kicks arse.http://www.symmetricom.com/products/frequency-references/chip-scale-atomic-clock-csac/Wish we had that option 7 years back or so in the seismic industry.

author: ddavidebor
author_rank: Super Contributor
timestamp: April 24, 2013, 09:55:08 am
content: there is china ebay an ovenized oscillator that use 5v and output a square wave.or you can use a normal ovenized oscillator with a step-up converter, but how much can a 9v battery last? 10 minute?

author: amyk
author_rank: Super Contributor
timestamp: April 24, 2013, 10:27:33 am
content: Quote from: ddavidebor on April 24, 2013, 09:55:08 amA 9V battery has around 500mAh, but relatively high internal resistance as they're not meant for high-current use.

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 24, 2013, 12:04:03 pm
content: i was thinking of a lithium 9v. 1000mah. and have a few in parallel.

author: saturation
author_rank: Super Contributor
timestamp: April 24, 2013, 03:27:54 pm
content: Your standard is only as good as the tool you measure it with, and if your counter is not as good as the standard, who is to say who is off? If you read the archives on the discussion regarding the Racal Dana 1996 and the difficulty adjusting OXCO, you'll understand you don't want to adjust it unless you can be there to tweak it for days if not weeks, to allow it to settle. That thread also has graphs, links and discussion as to which standard you want and why: OXCO, Rb, GPS disciplined, etc., Similar to this:http://www.oscilent.com/esupport/TechSupport/ReviewPapers/IntroQuartz/vigcomp.htmYou do not need to ship it anywhere for confirmation if you are using Rb or GPS disciplined, but you will need to for OXCO. However, they are very finicky to adjust. Given shipping cost and that used Rb oscillators run <$100, are far more accurate and need no calibration,getting an Rb one is better than calibrating an OXCO. Note, Rb oscillators wear out, ~ the rated life is 5-12 years, but the actual life can be longer. Those eBay ones taken as salvage are often pulled after their manufacturer rated life, but some folks have been able to rejuvenate the assemblies.http://www.vk3um.com/Rubidium%20rejuvination.pdfTo keep a standard, you'll really need a frequency counter that reads the ppm to your desired accuracy and top frequency than can use external as well as output a standard frequency. I would suggest you choose what the ham operators use, either a Racal Dana 1992, 1996, or 1998 or a HP 5334B or equivalent. At minimum, find one with an onboard OXCO as the cost is not that much more than without the OXCO. You can get any of them between $50-200, working. Using a stand alone crystal, with no counter >= to the crystal accuracy to confirm crystal accuracy, will be a lot of guess if not futile work.http://www.barrytech.com/hewlett-packard/counters/hp5334b.html