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Old 23rd Jul 2017, 3:49 pm   #46
G0HZU_JMR
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Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: Off Air Frequency Standards....

Quote:
Originally Posted by G8HQP Dave View Post
For off-air reception the issue is not how stable is the standard but how stable is the ionosphere. I vaguely recall seeing some discussion of that some years ago, but I can't remember where.
Yes, I think it's best to use these things during the daytime when the propagation effects are not so significant. I'm only 25 miles from Droitwich and I get good results during the day. However, to reliably get beyond about 2e-9 performance it's best to average over time and maybe recheck this several times a day.

To get the very best performance I think you are meant to average over several hours during daytime because the propagation effects can't cause a long term error. So it should be possible to get reasonably close to the performance of the BBC standard if averaged over several hours. But I'm not interested in getting this level of accuracy. I just want something that keeps my various 10MHz OCXOs in my RF test gear within about 0.1Hz of 10MHz. eg I have various items here that use a classic Agilent 1E5 10MHz OCXO.

I did check mine against a Quartzlock E8-Y GPS 10MHz reference a few years ago and it did seem to reliably deliver <0.01Hz error (at 10MHz) when averaged over about 10 seconds. This was done numerous times during the day. I did try averaging over longer periods but I can't remember how good the results were.

For me, the appeal of the 198kHz offair standard is that you can switch it on (with a small integral antenna) and get +/- 0.02Hz typical accuracy (at 10MHz) within a couple of minutes after switching it on. When I had the E8-Y GPS standard here I tried various tricks to upset it and it was easy to get it to give significant errors even when it still reported itself to be in lock. It also took ages to get lock and required an external antenna and monitoring via RS-232 to get a reliable signal that didn't cause it to misbehave. Too much hassle!

If the 198kHz service goes away one day then I guess I'll have to consider GPS. But for me the extra hassle involved (i.e. long and unreliable lock time and crap portability) make it a poor alternative because I don't 'need' better than 2e-9 performance.
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Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 23rd Jul 2017 at 4:03 pm.
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