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Re: [TowerTalk] Tower and antenna decisions

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Tower and antenna decisions
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 28 Oct 2013 11:39:47 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 10/27/2013 2:26 AM, Jim Thomson wrote:
#  Lemme rephrase that slightly.  IF the ground is relatively flat....higher
is STILL better.   The 1st 45 feet doesn’t count.  You need that just to clear 
junk +
clutter in the surrounding neighbourhood.

I won't dispute that.

## While 70 ft may seem high....on 40m + 80m, its not.   70 ft on 40m is like 
35 ft up
on 20m.

Gee -- from your earlier post, to which I strongly objected, I got the distinct impression you were talking about tribanders. But that is is exactly my point -- in addition to clearing the clutter, the most important contribution of height is forming the vertical radiation pattern of the antenna, and for that, height must be thought on in ELECTRICAL DEGREES, not feet or meters. Up to a point, additional height boosts low angle radiation, but eventually a height will be reached where it produces nulls in the vertical pattern. At lower heights these nulls are at higher angles, but when you go higher, they are at lower angles.

I'm currently in the midst of a project to raise my 80/40 fan dipole from around 120 ft (155 degrees on 80M) to around 140 ft (182 degrees) to improve its low angle radiation on 80M, and to add a reflector to increase the gain to the east coast and EU. If it were flat land, NEC predicts 2 dB for the increased height and 3.5 - 4.5 dB for the reflector (the lower gain number is because the available trees don't allow the reflector to be parallel to the driven. We'll see.

Take one of these 89 ft crank ups....and run it from 26 ft nested..up to
89 ft extended..and it’s a real eye opener.  I have a  slight uphill rise from 
N-S...all facing east.   And slightly downhill.... from N-S..all facing west.   I need 
all the height I can get when pointed at EU, AF, SA, etc.

Right, but you said flat land. I have similar topography here to the north and east, and on all bands, higher IS better in those directions, even on the higher HF bands. But it is NOT better to anywhere in the Pacific, because I have five miles of down-slope in that direction.

The beauty of N6BV's HFTA software is that it first models the contribution of terrain to the vertical pattern along any azimuth that you choose, then allows you to superimpose statistical modeled data for the vertical propagation to a range of destinations for the non-WARC bands. This allows the user to see when those vertical nulls are likely to get us in trouble, and when they don't matter. I have two towers, one holding a 3-el SteppIR (no trombones) at 120 ft, another placing monobanders for 20 and15 at about 45 and 35 ft respectively, and a third push-up holding a 10M Yagi at 20 ft. In all cases, HFTA accurately predicts the actual on-air performance of these antennas.

As to stacking Yagis -- I've heard W3LPL do an excellent presentation on this topic at part of K3LR's Contest University. I don't know whether this material is available on line, but it's well worth seeking out.

Someone objected to my use of "profanity" to make a point. The late Paul Klipsch, was one of the most highly respected of engineers working in pro audio as well as some other disciplines (explosives and firearms, as I recall), and founder of the loudspeaker company bearing his name. At annual meetings of the Audio Engineering Society, Paul made a practice of sitting at the back of technical papers sessions wearing a plaid sport shirt (and a bola tie, as I recall). When the technical content of a given paper strayed from the laws of physics, Paul would stand in the aisle at the back of the room and open his shirt to reveal a tee-shirt containing the single epithet "BULLSHIT" in large letters.

73, Jim K9YC


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