[time-nuts] Droitwich

Salisbury, JG (James) J.G.Salisbury at rl.ac.uk
Thu Apr 5 08:08:51 EDT 2007


Have a look at BS 7647,  the standard for radio controlled electricity meters. 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Peter Vince
Sent: 05 April 2007 12:21
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Droitwich

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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