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Re: [TowerTalk] Tower and antenna decisions

To: "TT TowerTalk" <TowerTalk@contesting.com>
Subject: Re: [TowerTalk] Tower and antenna decisions
From: GARY HUBER <glhuber@msn.com>
Date: Fri, 25 Oct 2013 12:00:31 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
The TH-11 appears to me to be a WARC enabled TH-7.... the log cell is just 20, 17, 15, 12, and 10 meter driven elements fed in log periodic fashion and with yagi type reflectors and directors on a 24 foot boom.
See http://www.hy-gain.com/pdffiles/TH-11DX.pdf for details.


73 ES DX,
Gary -- AB9M

-----Original Message----- From: Gene Fuller
Sent: Friday, October 25, 2013 11:38 AM
To: jim@audiosystemsgroup.com ; towertalk@contesting.com
Subject: Re: [TowerTalk] Tower and antenna decisions

Hi Jim -

Would you like to add any comments regarding LP's.  Granted, only as much
"gain" as a good two or three element yagi and no killer as far as F/B is
concerned, but no traps, no "critical" tuning, only one feed line, one boom
and only one rotator. For that matter the TH-11 uses a small log cell, with
no traps  for the "driven" element(s), and combined with parasitic directors
and reflectors, with  relatively few traps, should be a fairly effective
antenna, as should be the Tennadyn LP's

Gene / W2LU


----- Original Message ----- From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <towertalk@contesting.com>
Sent: Thursday, October 24, 2013 11:26 AM
Subject: Re: [TowerTalk] Tower and antenna decisions


On 10/23/2013 9:10 PM, Avery Davis wrote:
TH-11DX at 34 feet?
HexBeam at 50 feet?

As to gain figures for these antennas -- around 1999-2000, Ward, N0AX, and Steve, K7LXC, set up and measured a dozen or so tribanders on a tower under carefully controlled conditions. A few years later, Tom, N6BT, did similar work. Both found that the CLAIMED gain numbers for all of them (except Tom's Force 12 designs) were wildly inflated, often by as much as 6 dB. Two antennas that Ward and Steve measured actually had NEGATIVE gain as compared to a resonant dipole at the same point. You can buy a report on their work from K7LXC's website. It's $20 well spent. Steve also sells N6BT's "Array of Light," which includes his measurements and lots of excellent discussions of various antenna designs. I think it was $35.

One of the points that Tom made in his book (really a somewhat disorganized collection of essays he's published over the years) is that the most efficient antennas are simple monoband Yagis, and that when traps are added to cover multiple bands, the traps burn some of the transmitter power, and the shortened elements reduce radiation resistance (the part of the antenna impedance that accounts for radiated power), which also reduces gain. Thus, the gain of an ideal 2-element or 3-element Yagi is the BEST that can be achieved by an antenna with the same number of elements for that band. The advertised gain figures for the antennas that Ward, Steve, and Tom measured were 3-6 dB greater than for the ideal Yagis!

I would look at one of lighter-weight antennas that does not use traps. My 3-element SteppIR (the original with no trombones) works very well, have been essentially trouble-free for the four years it's been up, and is lighter in weight than most other antennas you are probably considering, which makes it easier to install safely. It has the efficiency of an optimized single-band Yagi on all bands, including the WARC bands. With the added fixed 6M element, it's also a very good performer on that band. No, it's not cheap, but given your constraints, it's a very good choice. Even the simple 2-element SteppIR would be a good choice, and can easily be handled by one person. I learned that when I helped N6KJ assemble his for Field Day several years ago.

I'd also look at the Force 12 antennas, none of which use traps, and which provide very good bang for the buck. The two that Ward and Steve measured were the best performers in both groups they measured -- small tribanders and larger tribanders.

73, Jim K9YC
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