[time-nuts] Droitwich Frequency Error

[Brian D]

Have you considered that there are two other transmitters (in scotland)
"synchronised" with the droitwich transmission.




You wrote:

> Hi Folks I've just joined this list, but have had an interest in accurate
> frequency measurement for decades, ever since finding a fully operational
> HP5061A in skip with what appears to be plenty of Cs life left in the
> tube.   It only gets turned on when needed here.    Anyway :
> 
> This morning, mainly to prove something it to myself I made a plot of the
> off-air UK Droitwich LF transmitter whose carrier is supposed to be a
> national standard - although I believe it uses a Rb source that is
> periodically updated with a Cs one - manually.
> 
> I have a Leo-Bodnar GPSDO had been turned on only some 20 minutes before
> the plot was started, as teh reference into a custom own-design LF
> receiver that gives a digitised baseband I/Q output to a PC.  Its LO is
> tuned using an  AD9852  48 bit DDS clocked at 10MHz and set by an
> algorithm that allows a micro-Hz but completely deterministic tuning error
> - it was this error I was trying to show by doing a plot of Droitwich off
> air using the GPSDO as a reference.
> 
> The plot at http://www.g4jnt.com/DropF/clipboard_202010181333.png shows
> the result - the phase is the red line.    My calculated tuning error at
> this frequency is 3uHz, but there is a slope to the line showing around 20
> degrees of phase shift in a little under 2 hours.   This corresponds to
> about 7.8uHz error. If my tuning error contributes 3uHz of this, that's
> still 4.8uHz on 198kHz , or 0.024 PPB.   It was well after sun rise, and
> the transmitter is only 100km away from me, so oughtn't to expect
> propagation anomalies
> 
> My question,  does anyone know if a GPSDO, has any inherent drift over its
> first hour or so?   I wouldn't have thought there was any mechanism for
> that, but who knows.
> 
> Finally, I guess 2.4E-11 isn't really outrageous for a rubidium source,
> even one that is 'supposed' to be corrected from 'time-to-'time' Or  Is
> it?
> 
> 
> Andy www.g4jnt.com _______________________________________________
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> 
> 


-- 
Brian Duffell   Yarm    England