[TowerTalk] Re: Why Are Some Stations Stronger When 20m Dies?
Michael Tope
W4EF@pacbell.net
Fri, 07 Jan 2000 09:05:42 -0800
David,
In order to better understand the north-south propagation on 20 meters, you might
want to spend some time on 20 meters during one of the major DX contests. What I think
you will find is that early on (just after your sunset) you will be hearing lots of
loud W stations as well as South and Central American stations. As the evening wears
on, you will notice that the W stations start to fade while the South and Central Americans
are still coming thru loud and clear. Mind you that the W stations that you will hear fading
are not going to be little pistol stations, they will be first tier contest stations
with big antennas and 1500 Watt amps (some may be greater!). I think you will notice
that the Caribean and Central American stations will begin to fade next, leaving
only the South Americans with big signals. You will still hear W's, but there signals
will be weak and watery as they will be coming to you via scatter over the South rather
than directly.
As far as your comments regarding stations in South Texas versus Mexico, you said Mexico
or therabouts. The thereabouts makes a huge difference, as propagation tends to be very
latitude sensitive. Stations in southern Mexico, or Costa Rica for instance will have
much different propagation than stations in Northern Mexico. That is the other advantage
of listening during a contest. You will hear stations in Central America working people
you can't even hear. This is mainly due to geographical differences and much less so due
to antennas (some of these stations may be running crude antenna which are much less
effective than your own), and definetly not due power since your are talking about difference
in receiving ability.
While I would concede that power may play a factor in the strength of these Spanish speaking
stations, the bulk of the effect is geographic (e.g. propagation). After all 10KW is only
about 8dB better than 1500Watts.
Mike, W4EF..............
----------
From: DavidC[SMTP:eDoc@netzero.net]
Reply To: DavidC
Sent: Friday, January 07, 2000 5:46 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Re: Why Are Some Stations Stronger When 20m Dies?
I really appreciate all of the responses to my question!
I apparently was unclear in my original post since many
responded that it was merely an issue of propagation ...
but none could explain why that might be so.
Consider the context that I presented:
1. The Source stations are believed to be in Mexico (or thereabouts).
2. The Receiving stations are in Both NH and FL.
3. The Spanish speaking Ham stations are exclusively strong
when US stations from coast to coast have all but vanished.
Why would not a South Texas Source be equally strong in NH and FL
as the "Mexico" Source? Why are only the "Mexico" Source stations
so uniquely strong to both NH and FL? I heard the same anomaly in NH
as I now hear in FL. Abusively high power has been suggested by some
as the explanation. Could it be that these stations are really only using
better antennas or benefit from some unique geographic-propagation
anomaly to NH & FL that *no* US station benefits from?
As for the larger issue of lengthening band openings the addition of a
quad and a vertical to the 20m antenna mix, perhaps at different heights,
has been recommended. Adding a second beam at a lower height has
also been recommended.
I have heard some of these recommendations before.
Has a careful study been conducted of this to document an optimum mix
of antennas for this specific purpose? I have only read here of two and
three beam stacks but not of the possible value of verticals, quads, delta
loops and other antenna configurations at various heights to also lengthen
communication time at the edges of propagation fade. Perhaps I missed
such a discussion?
- Thanks! & 73, DavidC K1YP in Hudson, FL
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