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
|
