Topband: HFTA, Radio Arcala, general comments

[Ward Silver]

> 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