From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 31 Jan 2001 12:50:15 -0000
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Subject: Re: LF: Morning noise levels
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G3NYK wrote:

> If you care to trawl Rik's web site there are several plots on 137kHz
> when CFH has gone off that indicate the noise here is related to the
> oncomming daylight.

What we need to establish is: Is this really 'oncoming daylight', that 
is at a different time for each latitude, or is it one event (for instance 
an Eu transmitter switching to low power) that is related to daylight at 
one location? In other words, do Geri and Marco see the effect at 
the same time as each other but at an earlier UTC time to the UK?

> My explanation of this 6dB decline is the shutting down of the area of
> received signals (including the storm areas)  as daylight approaches.
> Our biggest area of noises in the UK is to the east. The effect may be
> different in central Europe, it should be essentially symmetrical.
> This is based on the opposite effect which occurs in Canada where the
> S/N is best in the early evening, and degrades about 4 hours after
> sunset.

I have never before seen such a clear description of why this non-
reciprocal effect happens. Thanks.

Another interesting clue is given by the double wobbly lines very 
close to 137.790kHz and about 1Hz LF of Larry's beacon. I thought 
this was local to me but I see exactly the same on G3YXM's plots 
(see http://www.wireless.org.uk/newspic42.htm). My noise level 
takes a dive shortly after these lines suddenly stop. Dave seems to 
have exactly the same effect as can be seen from his third graph 
(note that the AGC in Argo causes the VA3LK signal/noise to 
improve but not the apparent background noise). How widespread is 
the reception of these lines (Dave and I are about 130km apart)? 
What are they? Do they disappear because of propagation, or 
something stopping transmission?

There is plainly a lot to learn and investigate here.


Mike, G3XDV (IO91VT)
http://www.lf.thersgb.net