Topband
[Top] [All Lists]

Re: Topband: HFTA, Radio Arcala, general comments

To: <topband@contesting.com>
Subject: Re: Topband: HFTA, Radio Arcala, general comments
From: "Ward Silver" <hwardsil@gmail.com>
Reply-to: Ward Silver <hwardsil@gmail.com>
Date: Wed, 24 Oct 2012 21:47:54 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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
_______________________________________________
Topband reflector - topband@contesting.com

<Prev in Thread] Current Thread [Next in Thread>