On Fri, 2008-09-05 at 20:52 +0100, Steve Hunt wrote:
> Jerry,
>
> Thanks for the info.
>
> I made final adjustments this afternoon by fishing out an old GC
> receiver and using it to receive WWV on 10MHz. I held a piece of wire
> onto the Omni TCXO divide-by-two chip output, and dangled the other end
> near the GC receiver. Using AM detection I was able to adjust the TCXO
> to within about 1/2Hz by listening to the "flutter".
That's exactly how its done. HF propagation isn't much better than that
if you average doing the same time every day for a month. If the crystal
trimmer had finer resolution you might be able to get down to a swish
sound every few minutes, but that takes a fine adjustment on the
oscillator and an oscillator that will STAY within 0.1 hz or better for
hours and normal TCXO won't do that good.
>
> Then I listened to the 40m broadcast band music station and adjusted the
> BFOs.
>
> I spotted a simple construction project which uses a ferrite rod antenna
> and a high gain TRF chip to produce a 198KHz output from the BBC
> Droitwich transmitter. That would form a crude, but useful, off-air
> standard. Droitwich used to be 200KHz, which made it simple to produce
> other reference outputs, but they changed to 198KHz some years ago when
> AM stations moved to 9KHz channel spacing.
Droitwich has the reputation of having very good frequency accuracy and
the LF propagation is more stable than HF, though there are detectable
phase shifts when aurora is imminent.
>
> Thanks again,
>
> Steve G3TXQ
>
You're Welcome.
73, Jerry, K0CQ
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