My comments?follow on three topics that have been brought up,
?
HFTA - It can import?the elevation angle files generated from
IONCAP/VOACAP that Dean N6BV produced. HFTA?does not have an ionospheric
module in it. And > yes, the files only go down to?80m because of
IONCAP/VOACAP limitations.
?
Radio Arcala - I have always believed that a horizontal antenna on 160m at
very high latitudes would?generally be worse (note that I didn't say
always)?than a
vertical due to the effect of the Earth's magnetic field. How?"theory"
translates to "the real world" is always subject to careful consideration,
but I've seen enough
data in the technical literature to stand by my belief.
?
Propagation on 160m - This is a very difficult topic. Most of what makes
160m go is down at D region and E region altitudes, and it is very tough
to gather data on
these regions at night. What data we have is mostly from rocket flights
and scatter radar - which gives us a model that probably doesn't capture
all the?
variability.?And I don't think we know all the mechanisms yet that give us
good propagation versus bad propagation.
?
Carl K9LA
Bob Brown NM7M (SK) wrote lots about propagation being quite a bit different
on 160 and MF because the ionosphere does not interact with the waves in the
same way it does at HF. The electron gyrofrequency (I just *love* saying
"gyrofrequency", don't you?) in the lower layers (what Carl is referring to
above) is much closer to 1.8 MHz and causes the wave coupling to change
dramatically in ways that are not well understood. This changes with
latitude and time of day (or night). There were a number of articles by Bob
about "ducts" between the layers that were very dependent on wave launch
angle to get into them. Such effects lead to odd propagation like the
frequently observed "spotlight" propagation and the high-angle antennas
hearing and working DX signals when low-angle would seem to be what "should"
work better.
My point is that applying models of ionospheric propagation that work at HF,
even 80 meters, often have a lot of trouble at lower frequencies because the
physics are different at those frequencies. That means you might need a
different approach to antenna system design than you would find successful
at higher frequencies. Things like improving system efficiency give the
same benefits but the most desirable antenna radiation pattern may not be
what you expect. Consequently, this is an area in which amateurs truly can
push the state of the art.
73, Ward N0AX
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