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LF: Transmissions from Donebach etc.

To: "LF-Group" <[email protected]>
Subject: LF: Transmissions from Donebach etc.
From: "Dick Rollema" <[email protected]>
Date: Wed, 31 Jul 2002 13:41:34 +0200
Reply-to: [email protected]
Sender: <[email protected]>
To All from PA0SE,

Many thanks to Andrew Talbot, James Moritz, Dave Brown, Alan Melia, Dave Pick, Markus Vester, Steve Dove and Ray Soifer for their reactions on my field strength measurement of Donebach and Droitwich.
I am happy that my findings have been confirmed by others.
As to the "downward modulation" of Droitwich: I found the same effect on the BBC World Service at about 648kHz.
The increase  of the carrier during brief moments of silence can be easily seen, not only on a selective voltmeter, but also on an oscilloscope that displays the signal. I checked that with the scope connected to the  30kHz IF of the W & G PSM-5 and also the 455kHz IF of my  pre-war HRO (with 2.5V heater valves!).

But you don't need sophisticated equipment at all. A receiver with an S-meter also shows the downward fluctuations on the BBC transmitters and the upward ones on Donebach,  Dutch 747kHz and several other stations on MF.

I don't think the phase modulation of some of the transmitters plays a role; when you listen to the transmission it is easily observed that the fluctuations follow the amplitude of the modulating signal.

73, Dick, PA0SE
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