[CQ-Contest] ionospheric absorption not heating
bjk at ihug.co.nz
Thu Apr 5 09:20:18 EDT 2001
Very interesting, Larry.
(It is moments like these that I realise that I know very little about the
physical fundamentals of ionospheric propagation)
I think we have all encountered the phenomenon of strong signals on an
otherwise dead band that Larry speaks of. My intuition was that it was due
to spotty distribution of ionisation.
A possibly related phenomenon:
These are relatively weak signals that appear as the only signals on the
band when the bands are closed or closing. In many cases these signals are
from quite modest stations, frequently using ground plane antennas.
My interpretation is that these stations have some significant very low
angle radiation which gets through under these conditions. When the band
opens up a little the stations with beams at good height are much stronger.
I was stuck with modest elevated ground plane type antennas on hf for years
and had the impression that they were quite good when bands were marginal
but a bit pathetic when the bands were open.
Barry Kirkwood PhD ZL1DD
Signal Hill Homestay
66 Cory Road
Waiheke Island 1240
----- Original Message -----
From: Larry N7DF <n7df at netmdc.com>
To: Contest Reflector <cq-contest at contesting.com>
Sent: Wednesday, 04 April, 2001 3:28 PM
Subject: [CQ-Contest] ionospheric absorption not heating
> The real factor in the anomalous change in signal strength between =
> qrp/qro signals is attributable to a threshold level of absorption in =
> the ionosphere. When the level of ionization drops below a certain =
> level, a signal must exceed the absorption potential before it will be =
> refracted and intercepted by ground based stations. This is easily =
> noticeable during band opening and closing periods where stations with =
> exceptionally tight beam signals break through with loud signals while =
> the majority of stations are not even heard.
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