LF: Transmissions from Donebach etc.

["Dick Rollema" <d.w.rollema@freeler.nl>]

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