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Re: [TowerTalk] Take off angles, VOACAP, etcf.

To: "Guy Olinger, K2AV" <>,"TowerTalk List" <>
Subject: Re: [TowerTalk] Take off angles, VOACAP, etcf.
From: "Jim Lux" <>
Date: Sun, 17 Oct 2004 08:51:39 -0700
List-post: <>
This brings up an interesting idea...
As was recently suggested, it's easy to work the guy with the beam up 100
feet running a kW (for which path your take off angle will be low), but to
work the guy with the dipole at 30 feet with 100W, you would need a high
angle, to match his high angle.  Sure, it's the multihop path, but the
increased loss might be made up for by the increased gain on the high angle
launch at each end.

Fascinating.. and one that VOACAP isn't going to be suited to analyzing. I
was just reading the technical manual and there's a lot of  funky
assumptions that it makes  when calculating path losses on many hop paths.
As Guy has pointed out, those assumptions are valid for broadcasters or for
people running HF comm links, both of which are interested in link
reliability on a 24/7 basis, but may not be for hams, who have a very
different operating style.

For instance, things like grayline propagation might be perfectly useful for
hams, who can wait for that optimum time to make the QSO.

This is all quite fascinating. If you are designing an antenna installation
for hams (or, if as I am doing, you are looking at optimizing phased arrays
for hams), the ionospheric effects might actually be less important than
such things as the antenna configuration on the other end of the
(speculative) link and the relative times of day, and, in the contesting
scenario, what all the other hams are doing.  Hams can work with quite low
SNR, and with a lot of fading, so as long as "some path" is supported at the
frequency of interest, you can potentially work the other end.  (Of great
interest is the recent research showing that polarization diversity
combining can greatly reduce the fading (particularly the frequency
selective nature of it), at least on your receive end... can't do much for
your Tx path, though)

----- Original Message -----
From: "Guy Olinger, K2AV" <>
To: "TowerTalk List" <>
Sent: Sunday, October 17, 2004 8:11 AM
Subject: Re: [TowerTalk] Take off angles, VOACAP, etcf.

> In terms of the simple math and numbers, you are correct. But to USE
> the numbers to make a construction decision is where the other
> considerations come in.
> If you use VOACAP running under "poor" station restrictions, you DO
> come up with different figures. Angles that a broadcaster would pick
> in a heartbeat are not allowed to surface without a penalty, and
> powers used preclude use of a weaker but more "reliable" mode with
> higher transmitted level by the broadcaster.
> Guy.
> ----- Original Message -----
> From: "Bill Aycock" <>
> To: "Jim Lux" <>; "Jim Lux"
> <>; "Guy Olinger, K2AV" <>;
> "W3YY" <>; "TowerTalk List" <>
> Sent: Sunday, October 17, 2004 7:44 AM
> Subject: Re: [TowerTalk] Take off angles, VOACAP, etcf.
> >
> > Is my intuitive logic wrong? It seems to me that the antenna has
> > nothing to do with the characteristics of the ionosphere; it only
> > controls ones ability to accept and use the signals that are there.
> > Bill
> >


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