From: "John W Gould" <g3wkl@btinternet.com>
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: Re: AW: Strange signal on 135 kHz...
Date: Mon, 28 Jan 2002 19:22:44 -0000
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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: majordom@post.thorcom.com [mailto:majordom@post.thorcom.com]On
Behalf Of jannsen
Sent: Monday, January 28, 2002 17:55
To: rsgb_lf_group@blacksheep.org
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 dj8wx@qsl.net