[time-nuts] Droitwich

[Peter Vince]

Note specifically that the 198 KHz signal is phase modulated by 
low-speed data.  John's link below reproduces an old BBC information 
sheet with details.

I have just had a quick play with the "Spectran" audio spectrum 
analysis and waterfall display program (http://www.weaksignals.com/), 
and that clearly shows close-in sidebands at ± 12.5 Hz etc.  Compare 
that with the French station on 162 KHz, which has "noise" (well, OK, 
audio modulation) all the way down to the carrier - the "BBC Radio 4" 
signal on 198 KHz clearly has a high-pass filter on the audio 
modulator so the audio doesn't interfere with the slow phase-mod data.

I'll try and find out if there is any later information about the 
data that is phase modulated.

	Peter Vince  (Snr.Engr., BBC TV, London)


>Neville Michie wrote:
>> Hello all,
>> I have a HP 5090A fixed frequency receiver which I believe was made
>> to recover
>> precision frequency signals from Droitwich radio station.
>> I can not find any technical information on this receiver, can anyone
>> tell me
>> is Droitwich still active as a stable frequency reference, and where
>> can I find a manual for the receiver?
>> cheers, Neville Michie
>>
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>See http://tx.mb21.co.uk/gallery/droitwich/droitwich-lf-data.asp - half
>a megawatt now on 198kHz
>
>John
>
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