[TowerTalk] Mosley Antenna Question

[Jim Brown]

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