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Re: [TowerTalk] Mosley Antenna Question

To: jim@audiosystemsgroup.com, towertalk@contesting.com
Subject: Re: [TowerTalk] Mosley Antenna Question
From: TexasRF--- via TowerTalk <towertalk@contesting.com>
Reply-to: TexasRF@aol.com
Date: Sat, 21 Feb 2015 19:20:03 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Jim, have you considered switching the reflector to a director for long  
path? Sounds like your stub switch might allow that.
 
73,
K5GW
 
 
 
 
 
 
In a message dated 2/21/2015 5:20:47 P.M. Central Standard Time,  
jim@audiosystemsgroup.com writes:

On  Sat,2/21/2015 12:51 PM, Rick Stealey wrote:
> Yes, but you are comparing  your dipole with the same dipole plus 
reflector.

No. I did that a year  ago when I first rigged the reflector. This 
morning, I was using the  antenna as a dipole on long path. I had 
achieved a 2 dB improvement by  raising the antenna from about 115 ft to 
about 135 ft.

I raised  both wires in the last few weeks. That increased height also 
helped it by  2 dB.

This does, of course, clearly illustrate the value of a few dB  here and 
another few dB there adding up. When I first rigged those high  dipoles, 
I was feeding them with much smaller coax -- RG59, I think.  Modeling 
(using TLW, which comes with the ARRL Antenna Book) showed that I  could 
gain another dB or so by using a good RG11 -- I got a good deal on a  big 
spool of Belden 8213 and used that. I chose RG11 because it had less  
loss due to mismatch at the band edges, because the high dipole is a  
better match to 75 ohms.

> Have you considered how to make  meaningful measurements on your array?  
Say, to determine the frequency  of best f/b?

No. Can you suggest a method that doesn't require a drone  with 
instrumentation?  :)

> I think you also have a  Steppir.  How do you know it is tuned on each 
band for the best  performance?  (the three models that are programmed into 
the controller  for each band).

I've never taken the time to investigate that. I could,  if I wanted to 
take the time, plot its pattern by recording field strength  as I rotate 
it, but that wouldn't tell me the gain. And when I've thought  of doing 
that, more pressing issues have always gotten in the way --  anything 
from repairing gear, to repairing storm damage to antennas, to  upgrading 
the shack, to improving the antenna system, to making the XYL  happy.

Modeling with software like NEC is pretty accurate when properly  used.  
Some studies I've done show the value of raising a horizontal  antenna to 
improve the vertical pattern, putting more field stength at low  angles. 
In addition to getting the 80/40 dipoles (and the reflector)  higher, I 
also moved my 30M dipoles from about 35 ft to about 100 ft. They  also 
play a LOT better. A few days ago, I worked a C5 on 30M. He was a lot  
louder on the new antenna than the older lower one (which is still  
there, for comparison). You can see my work at k9yc.com/publish.htm   
Download the slides (pdf) about antenna planning for small  stations.

73, Jim  K9YC
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