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Re: [TowerTalk] If you had a choice

To: <>
Subject: Re: [TowerTalk] If you had a choice
From: "Ward Silver" <>
Reply-to: Ward Silver <>
Date: Tue, 16 Oct 2012 17:12:49 -0500
List-post: <">>
Mosley's PRO-57B claim of 8.5dBd gain on 20m with only a 24' boom is incredible

That gain spec originated many years ago when it was common practice to include ground gain (up to 6 dB) in the figure. The practice of only using free-space gain in dBd is a relatively recent innovation that came about after antenna modeling became widely used. Without the ground gain included, a free-space gain of 2.5 dBd (4.65 dBi) on a 3/16-wavelength boom is quite a bit more reasonable. (It's probably a little higher than that with no effects from the feed line causing possible pattern distortion.) On 20 meters, the PRO-57B was within reach of the other designs and you wouldn't have noticed great differences on the air.

As a useful benchmark for sanity checks, I recommend the optimized set of Yagi designs developed by Dean Straw, N6BV for the ARRL Antenna Book. The program YW (Yagi for Windows) gives reasonable, reproduceable gain figures for Yagi antennas. The venerable NBS Tech Note 688 ( also provides some guidance about what is practically achievable.

Remember that fixed-spacing tribanders are going to be a compromise on two of the bands so you're going to have tradeoffs. And even an antenna with modest gain can be wicked loud if it is at the right height at the right time on the right band.

73, Ward N0AX

That is correct. We used a Force-12 1:1 bead balun (i.e. common-mode choke) on all of the other antennas, including the reference dipole, except for the KT-34XA which came with a 4:1 balun/transformer.

There are a number of stations with good signals, using Mosley beams. Most notably, K4RO has a pair of them and does quite well. He also has an extraordinary ridge-top location and has taken great pains to locate the antennas and towers to take advantage of that location. As in real estate - location, location, location. I used a Mosley Classic 36 at W0EEE for years, myself, with pretty good results.

The Mosley manual we had with the loaned PRO-57B (I think it was a B model) gave specific instructions how to construct the coax pigtail and said specifically not to use any additional devices at the feed point. It has been a long time since we did the tests (11 years, I think) and it is quite likely that the manual has been changed to recommend a common-mode choke. I would applaud that change as good practice. Feed line interaction could have certainly affected the results on one or more bands. We followed the rule of doing what the manufacturer said to do.

73, Ward N0AX

Date: Tue, 16 Oct 2012 10:14:21 -0400
Subject: Re: [TowerTalk] If you had a choice
Message-ID: <>
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Was this test run with no choke at the feed point of the Mosley and the
other antennas in your test had one?

To: "Towertalk Reflector" <>
Subject: Re: [TowerTalk] If you had a choice
From: "Ward Silver" <>
Date: Tue, 16 Oct 2012 08:09:51 -0500

A cautious word of defense on Mosley...the PRO series was definitely not
the top performing tribander in the tests ( but they
are built like tanks (that also means they are very heavy antennas) and do
stand up to the elements, particularly ice loading.  The Mosleys would
probably also benefit from decoupling the feedline shield with common-mode
chokes (ferrite or
coiled-coax) although the manual I saw during the test said not to use a
balun for some reason - that may have changed.

I agree with whoever said to avoid quads in Alaska - unless you like
rebuilding antennas :-)

Check with other KL7s in your area as to what they have put up that makes
it through the storms and gives adequate performance on the air.  In
extreme weather environments, there are more requirements than just gain
to worry about.

73, Ward N0AX


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