[TowerTalk] Tower and antenna decisions

[GARY HUBER]

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 at audiosystemsgroup.com ; towertalk at 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 at audiosystemsgroup.com>
To: <towertalk at 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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