[TowerTalk] Antenna Selection Assistance - thread drift

Robert Chudek - K0RC k0rc at pclink.com
Tue Jul 29 12:54:55 EDT 2008

I eluded to the fact that asking about antenna comparisons has a large 
component of personal bias (I bought it and use it so it must be good) and 
little reproducible comparison statistics (even the K7LXC & N0AX report 
acknowledges the technical difficulties comparing antennas).

[personal bias] Prior to my tower crash in 2003 I had a Mosley PRO-67B up 90 
feet. It covered 40 ~ 10 meters, excluding 30 meters. With 2 elements on 40m 
up that high it worked well. Although not designed for 30m I even made 
contacts on that band. I used the internal antenna tuner in the rig.

My original intention was to install another antenna that covered 40 ~ 10 
meters on a single boom. I was looking at the Force 12 and the bigger Mosley 
products when an TH-11DX became available in an estate sale. I asked around 
the DX club and was surprised that many of the top DXers in my area were 
using this antenna. It wasn't peer pressure but more like peer 
recommendations that convinced me to buy the TH-11DX. And it didn't hurt my 
"ham ego" that this used antenna was priced about 50% off retail.

When I picked it up, the antenna was in "chunks"... it had been disassembled 
only to the point it could be bundled together in pieces 12 ~ 15 feet long. 
This was a perfect length for strapping to the rooftop carrier on my van. It 
took me more than several days to take it apart, clean up the joints, 
replace corroded fasteners, and reassemble the beam. I wasn't in a 
particular hurry but the thought that purchasing a new antenna and 
assembling it would be a better value if you didn't have the time to putz 
with a project like this. There were several trips to the hardware store for 
small fasteners and stainless hardware.

My replacement tower is 70 feet and this is where the TH-11DX rides. The 
antenna is on a 24 foot boom which holds 11 elements. The driven elements 
are the standard Hy-Gain log periodic design and the reflectors are full 
sized. Only the directors have traps for 10 and 15 meters. The antenna is 
heavy, close to 100 pounds if I remember correct. It includes the BN4000 
current balun which is rated for 2000 Watts continuous and 4000 Watts peak.

I ran VSWR sweeps with the antenna mounted on a 6 foot pole before I put it 
on the tower. I wanted to make sure it was going to resonate in the ham 
bands. It looked reasonable (I didn't keep those graphs) so I installed it. 
I then ran sweeps by connecting my analyzer to the pigtail at the top of the 

You will find the 5 files on my website http://chudek.aberon.net in the AEA 
HF ANALYST CHARTS folder. Go into the TH-11DX folder and download the PDF's. 
You will also find sweeps for two other TH-11DX's at K0IEA and KF0QR. These 
were taken from the shack end of their feedline so there will be some 
transmission line bias in these values. In addition, all three antennas are 
at different heights; 50, 70, and 90 feet which complicates direct 
comparisons even further. Add into the equation these antenna locations have 
different terrain and any direct comparison is futile. But I had a new toy 
(analyzer) and had fun using it.

ASIDE: Regarding transmission line bias, you can download the 160m inverted 
vee chart found in a separate directory. I made two measurements; the first 
directly connected to the feedpoint and the second at the end of 1/2 
wavelength of RG8x coax. As you know, a 0.5 wavelength transmission line 
should present the same feedpoint values to the transmitter end. I overlaid 
the two sweeps on one graph so it is easy to see how a feedline can "bias" 
the results. In the case of 160m 3:1 bandwidth, it looks like you have an 
extra 40 KHz of bandwidth due to this phenomenon.

So what's this long winded message really saying? Pick an antenna for it's 
match to your needs and goals. These are usually a combination of cost, 
product availability, available space, tower capacity, band coverage 
desired, durability, and reputation. Busting through a pile-up also depends 
upon operator skills.

Regarding my 40m coverage... do I miss that? Well kind of. But I solved that 
issue by side mounting a single element, full sized Telrex 40m dipole at 65 
feet. And I also installed a sloping wire dipole. I find it interesting that 
95% of the time the Telrex hears better but there have been times when I 
could hear a station on the wire that was simply not audible on the 
horizontal antenna. Would a 2 element yagi make a difference? I don't know.

So is anyone interested in buying my 3 element 20m Gotham yagi, new in the 
box? :-)

[/personal bias]

73 de Bob - K0RC in MN

----- Original Message ----- 
From: "Richards" <jruing at ameritech.net>
To: "Robert Chudek - K0RC" <k0rc at pclink.com>
Cc: <towertalk at contesting.com>
Sent: Tuesday, July 29, 2008 1:12 AM
Subject: Re: [TowerTalk] Antenna Selection Assistance

> Excellent analogy, and yet I think it is still a fair question... 
> notwithstanding how it open ended it might be.    I like red cars!!
> Man.. I looked up the HyGain TH-11DX on rig pix... and it  is
> REALLY BIG.   No wonder you like it!
> If it was originally "temporary" -- what was the alternative antennas you
> had considered putting up there after wards, but did not, because it
> works so well.  In other words, what were the other "Leading Contendas"?
> Thanks.
> /////////////////////  K8JHR  ////////////////////
> ===================================================
> Robert Chudek - K0RC wrote:
>> A HyGain TH-11DX. It was going to be a temporary antenna for me
> but it works so well I'm leaving it up there at 70 feet.
>> But you do realize you're asking us what color car you
> should buy next, right?
> ==================================================

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