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RE: [TowerTalk] Stacking Problem

To: "David Robbins K1TTT" <>,"reflector -tower" <>
Subject: RE: [TowerTalk] Stacking Problem
From: Pete Smith <>
Date: Sun, 15 Feb 2004 12:38:13 -0500
List-post: <>
At 04:54 PM 2/15/04 +0000, David Robbins K1TTT wrote:
I am not surprised.  The added gain when running both is not the big
reason for stacking on hf. though you do get some small gain with both,
the big reason is to fill in gaps in the takeoff angle pattern.  On 40m
at 150' you may notice this if you happen to find a station who is much
weaker on one than the other, but when running both he is almost as loud
as on the single antenna that was the strongest before... that is the
real test that stacking is working, but it takes a lot of comparisons to
find a perfect example because of all the variables.

The only things I would add are --

It's unlikely that the RCS-4 is any part of the "problem."

It's not at all surprising that you can't hear any particular difference between the top antenna and the stack. I modeled the stack versus the top antenna over flat terrain with HFTA -- from 2 to 8 or 10 degrees takeoff angle, the traces are virtually identical. At peak gain, the stack registers 14.4 dBi at 15-16 degrees takeoff angle, while the top antenna shows 12.8 dBi at 13-14 degrees. Both peaks are a little high for best coverage of the statistical distribution of signals from Europe, but the real point is that the difference in signal strength is probably too small to hear on most all signals.

The dramatic difference in the modeled patterns is in the vertical breadth of the first lobe. The single antenna has 11 dBi gain or better only from 8-18 degrees takeoff, while the stack extends that out to 8-25 degrees. Statistically, to Europe again, this should be trivial, because the percentage of signals that arrive at angles above 18 degrees is very small. However, the real ionosphere often supports multiple propagation modes, some perhaps at higher angles than modeling would predict, and the mix can change rapidly. Adding of these various modes at the receiving array could account for some of the benefit from stacks, particularly in resistance to fading.

In my experience on the east coast, I almost never hear a difference between my top antenna and my full tribander stack, though fading does usually seem to be less with the stack. On the other hand, there are times when the bottom antenna is distinctly better, particularly in the middle of a European opening.

73, Pete N4ZR
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