From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Fri, 10 Aug 2001 12:45:28 +0000
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Subject: Re: LF: ZL DX testing 21 September
Message-ID: <E15VAhJ-0004e3-00@gemini.herts.ac.uk>
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Dear Bob, John, LF group,

I heard the Russian station on 171kHz for the first time last night - 
it shut down at 2000 utc as John says, but was only audible from 
1900 at my QTH, which might have been due to propagation, or 
then again, it may just have been on the air for an hour. I have not 
heard it before when monitoring this frequency, so it may have 
very limited operating times. 

After it had closed down, another station was audible on the same 
frequency, with what sounded like Arabic music playing, but this 
was considerably weaker than the Russian station. Looking at a 
spectrogram display at frequencies close to 172kHz, the effect of 
this QRM was not unlike the "Luxembourg effect" noises often 
heard at the top end of 136k. The net effect was to raise the noise 
floor by a few dB, although QRN was still the main source of noise.

Of course, one way to improve the situation would be to null out 
the offending noise with a loop - if the wanted signal from ZL 
comes over the pole, and the unwanted signals originate in Russia, 
this should work fairly well - does anyone know what bearing a 
signal from ZL should arrive on?

It seems strange the LF spectrum does not get used much "down 
under" - I would have thought it would work very well with all that 
ocean to propagate over.

DBF 39 transmits a carrier on 138.83kHz most of the time, 
interspersed at intervals of several seconds with short bursts of 
FSK data, mark 138.83kHz, space 139.17kHz. On a spectrogram, 
it will look like a 138.83kHz carrier unless a very coarse resolution 
is used.

Cheers, Jim  Moritz
73 de M0BMU