[time-nuts] Another "atomic" clock question
bob at evoria.net
Tue Mar 4 13:21:26 EST 2014
You may have missed TVB's post yesterday, quoted below. A "hanging bridge" is an area on a timing receiver's plotted sawtooth correction value that stays on one side of phase zero for some period of time. As a result of this "bias", a GPSDO that is not corrected for sawtooth will probably have at least a phase shift in its output frequency during a hanging bridge. It's not so bad on the newer 10ns receivers as it was on the older +/-52ns Oncores. If one could prevent these hanging bridges, an uncorrected GPSDO would likely track phase better. Tom suggested to detect when the bridge forms and give it a shot of heat. I suggested to vary the oscillator's frequency by periodically heating and cooling it.
"Sure. In fact you can loosely phase lock it to GPS that way. Your xtal
doesn't need to have an EFC pin. You are using external temperature as a
replacement for EFC. Call it TFC (temperature frequency control)
instead. You can't get much simpler than that. Make sure to use a plain
XO (not a TCXO or OCXO).
I used a resistor heater to bust hanging-bridges: http://leapsecond.com/pages/vp/heater.htm
> From: Tom Holmes <tholmes at woh.rr.com>
>To: 'Discussion of precise time and frequency measurement' <time-nuts at febo.com>
>Sent: Tuesday, March 4, 2014 12:07 PM
>Subject: Re: [time-nuts] Another "atomic" clock question
>Hanging bridge? What is it; where is it found; and how does it form?
>My guess is that a Google or Wikipedia search is going to come up with
>something named Golden Gate or maybe a musical term.
>Tom Holmes, N8ZM
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