Message-ID: <000601c2380d$7739c440$35337bd5@main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Subject: LF: Droitwich Carrier
Date: Tue, 30 Jul 2002 22:08:00 +0100
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Hi all, I was fascinated by Dick's measurements I decided I would swing the
radio onto Droitwich and switch through the filters.

The measurement was made at 2015z tonight Tuesday.....a science program
about George Best's liver!! So the modulation was all  male speech.

I switched through my filters with the AOR 7030+ on AM with the filters
centered on the carrier. The RX had 20dB of front end attenuation and the IF
gain was substantially reduced (AGC OFF) to give a three-quater scale
reading on the WB mV meter.  Measurement was made on the 455kHz IF output
with a B & K 2426 wideband millviltmeter in the "Fast" mode (timeconstant
around 0.5seconds I believe) I did not have time to lug a scope in from the
workshop.
Filter band is:-
300Hz
500Hz
2100Hz
3700Hz
6000Hz
9500Hz
In all positions the needle deflected downwards by 1.5 to a max of 2.5 dB on
speech peaks. I confirm Dick's comments this is definitely "downward
Modulation"  The result was confirmed using both the Mean and RMS detectors
on the B & K.. Next the wider filters were offset to accept just one
sideband (much better quality), and the WB mV meter still defected
downwards, by about the same amount , maybe a little less.

>From my rememberance of a visit to OrfordNess (BBC WS) the
500kW transmitters there have two valves connected by a quarter wave
"lumped component" line. One valve handles the "bottom half" of the waveform
and the second valve provides the power for the positive modulation peaks
only. Maybe they are using an old valve (Bargain from Proops ??) in the
second slot or it is not quite adjusted properly. .....or else maybe the
compressor is working overtime.  The BEEB dont admit to using  compression
but they jolly well do.  I think we have some Stateside lads with BC
knowledge who may be able to fill in the gaps. I am probably 200kms South
East of Droitwich (I havent checked)

That was an interesting ten minutes, I very nearly got interested in
listening to the descriptions of the likely state Best's liver !!  I think I
could use a drink !! Tea of course!

Cheers de Alan G3NYK    JO02PB
alan.melia@btinternet.com