I couldn't find the e-mail from Andre', but I have found a very detailed
explaination put forward by Peter, G3PLX, when the topic was discussed on
this list in 1998. This e-mail is on an earlier mail application that I am
currently using, so I have had to copy and paste. Attached is a more recent
e-mail from Markus, DF6NM, on the subject.
73 John, G3WKL
From Peter Martinez G3PLX Kendal Cumbria (1st Sept 1998)
I listened to 139 kHz last night too, with a separate BC receiver to
check the identity of any crossmod.
For me, there were at least two programs audible. I identified one as
France Entere (Is that how you spell it?) on 162 kHz. There was another
with a very characteristic Interval signal consisting of a two-note
rising-third (musical notes B and E), but I couldn't find the source of
it on the LW band or MW bands during the 5 minutes it was sending this
up to 2100utc.
The theory of D-layer modulation which results in this effect needs the
D-layer electron temperature to change in sympathy with the AM
modulation. The thermal time-constant of the D-layer varies, but is
about 60uS at a height of 75km and 600uS at a height of 85km. This
should mean that as the night approaches and the reflection height
increases, the cross-modulation should get progressively more ""top-cut"
to it. 600uS means a 3dB top-cut of about 260Hz. I wonder if anyone is
getting a strong enough cross-modulation audio to tell if it does have
this "top-cut" effect and if it varies during the evening?
The cross-modulation may be 180 degrees out of phase with the original
audio at the point in the D-layer where the effect occurs, but the
signal from the original transmitter, if it's a medium-wave one, will
probably arrive by E and F layer at night, a longer path than the LF
transmitter via the D-layer (at about 90km height). There will probably
be two other effects which will swing the phase of the cross-modulation.
The D-layer modulation will probably have a phase-modulation component
itself, and in addition, since there will be a lot of surface-wave from
the 139 kHz signal, the resultant received signal will arrive by two
paths and so the cross-mmodulation may even be phase-modulated or end up
in phase with the priginal audio. I plan to try using the stereo DSP
here to study this. It should be possible to integrate-up the faint
effect and cancel out the noise and static over a period of time. There
is no severe frequency stability problem doing this as there was
integrating the LORAN noise.
The wobble on the 183kHz transmitter is a burst of +/-90 degree phase
modulation sending a 24-bit 010101 pattern at 125 bauds, repeated at
intervals of 192mS. My guess is that it's a test pattern intended to see
if listeners are disturbed by it, preparatory to introducing a data
broadcast on it, as is done on several other LW broadcasts. On these
others, the phase deviation is usually only 30 degrees.
73
Peter
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of jannsen
Sent: Monday, January 28, 2002 17:55
To: [email protected]
Subject: Re: LF: Re: AW: Strange signal on 135 kHz...
Marco Bruno schrieb:
The interfering station will be different for every listener, since it
depends on the geometry of the phenomenon... it was widely
discussed on this reflector at the origins (three years ago...?)
when we were not sure it was Luxembourg effect; at the time
I presumed it was a defective emission from Europe 2 near
Saarbrucken on 183 kHz or so.
The modulation is wide, distorted and lacking high frequencies
because of the thermal time constant of the ionosphere... a curious
thing, that confirms that you are not hearing a spurious emission.
Also, at times more than one station may be received.
I may forward the relevant messages to anyone interested; I
remember a very good explanation by Andre' Kesteloot.
73 - Marco IK1ODO
Hi Marco,
you are right. here in the northerm part of Germany it is the
modulation from the DLF on 153kHz. it is daily abt an hour at
sun-set ZOA (maybe at dawn too).
Marco, I`m vy interested in that massage from Andre.
regards
Uwe/dj8wx [email protected]
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