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[TowerTalk] TH7DX summary

To: <>
Subject: [TowerTalk] TH7DX summary
From: (Carlos Augusto S. Pereira)
Date: Wed, 19 Mar 1997 13:08:26 -0300
Thank you fellows! I will take a look, if the antenna is OK I will buy it
for sure.

73, Carlos - PY1CAS



TH7DXX very good yagi.  The Mosley is a good yagi too, but not in the same
group as the TH7.
You'll enjoy much improvement with the TH7.  I have Mosleys CL33's for fixed
direction fill yagi's, and mono's as well, but a stacked pair of the TH7's
does great, as would a single TH7.

Happy Hamming,


Carlos, according to the Honor Roll DXers near me in new york, the TH7 is 
the most superior antenna for DXing. They all have one. And they all get 
through every pileup quickly, I've seen them in action. Buy the damn 
antenna from the guy, and put it up. You wont be sorry. -pat


The Hy-Gain antenna range is much more suited to testing F/B than
forward gain.  If you were an antenna designer, you'd know that many times
when you decrease the amount of signal off the back of the antenna, the
energy that goes out the front of the yagi increases (more F/B, more gain).  

     Of course they cared about gain!  The fact that the TH6/TH7's are
probably the most popular high performance tribanders ever made and used by
thousands of hams around the world shows how successful Hy-Gain antenna
designers were in creating an antenna that REALLY WORKS.  

     The TH7 and the KT34XA are practically identical in terms of on-the-air
performance IMO.  

     I don't know what a TH7DXS is except it probably means Stainless Steel

    TOWER TECH has a reprint of a test done in the 80's that compares 10
different triband antennas.  It's not the definitive antenna test but does
give you more information in regard to your questions.  An SASE to TOWER
TECH, Box 572, Woodinville, WA, 98072, USA, will get you a free copy.

The S in "DXS" may refer to stainless steel hardware, nice to have but 
won't affect performance...if that's what the S stands for.

I more often hear of the TH7DXX.  Anyway, I didn't know there were 
different versions of this antenna, with the possible exception of 
non-stainless hardware being standard and stainless being an upgrade.  
Then again, maybe they call came with stainless, not sure.

I would think the TH7 would be what I call an "incremental improvement" 
over the TA-33.  It may even be more than one "incremental improvement 
unit..." maybe two, even three.  What is an incremental improvement 
unit?  The unit of improvement that is noticeable.

I would think this would be an improvement worth the trouble and 
incremental cost.  I suppose we could also discuss "incremental cost 
units."  hihi.


Another way to think of the TH7 is that it has more active elements on each
band than the TA-33. 



Carlos, the 7 is a worthwhile stepup over the TA-33. And remember, anytime
you optimize the
F/B ration, you must, by definition increase the forward gain also. 

By the way, I added an addition director to my old TA-33 about 30+ years ago
and it made
a significant difference. So if you can pick up the traps for the director,
just add aluminum
and extend the boom.


Name: Ed Sleight
To: <>
Date: 3/18/97
Time: 5:57:09 PM

Carlos, I do not know what the gain of a TA-33 is compared to a TH7DX but
I suspect the TH7DX will provide about 2 dB or more gain (on average on the
three bands) than the TA-33..... that's just a guess.  My guess is based
on the length of the boom, the empirically optimized TH7DX design and the
number of contesters that use the TH7DX.  I know of some hams that would
kill for another 2 db!!!! (myself, for one!  My wife for another!!).

As for the statement that the Hy-gain engineers optimized the F/B and didn't
care about the Fwd gain: don't you believe it.  That is hogwash.  Otherwise,
why would so many DXers and Contesters use the TH7DX?

Good luck in your decision.  Rod, W5HVV


      You cannot compare a ta33 to a th7dx!Do yourself a favour and buy
it.It "talks" as well as any 4el mono-bander on 20mtrs,and will last
forever.I have made more than 30,ooo q`s with mine and can still
generate the odd pile up or two.


I have bought about 3 used TH6s and 2 Used TH7s...I have 3 
stacked on the tower, and some for parts...They are good
antennas, I would expect a MAJOR improvement over the TA33.

Although not big compared to big monobanders, many are available used
because they were TOO BIG for the QTH.  If you
have room and a good tower, and a Ham M or better class of
rotor, then the TH6 is worth the extra trouble.  If your tower is not very
strong, your guys not decent, your yard
very small, then think about how you will put up the TH6.

If you can do it, its worth it.

73 Chas K3WW  

>Hi Carlos, by all means go for the TH7DX.  I believe the "S" stands for
stainless hardware
was used.  A few years ago I went from a CL-33 to a TH7 what a difference.
the TA-33 has three
elements on a short boom. With the TH7 you have a longer boom and 4el on 10.
The spacing for the 
three elements for both 15 and 20 is much much better than the TA-33.  I say
go for it, if you
can handle the physical increase in size i.,e., tower etc.  Good Luck 73
Pete N4KW

The TH7 is around 60 lbs.   Make sure you & ur gear can 
handle the additional load.
73 Robert  W5AJ   


Hi Carlos.  I used to run a TA-33jr and I also made it bigger with 4 elements
for 10m.  Then I bought a Quad... the difference was like changing from a
dummy load to an antenna.  I guess it will seem the same if you change to the
TH7 but of course even a TH7 is no match for a Quad.

Vy 73 de Bren G4DYO



My 2 cents says that the TA-33 is little better than a dummy load.  It
has less than unity (0 db) gain on 20 meters [check it for yourself -
put up a dipole at the same height - the dipole will be an S unit
better].  It approaches 0 db gain on 15 meters and maybe a few db on 10
meters.  The traps are very inefficient.

I have never owned a TH7DXX but I did own a TH6DXX for many years.  It
was a good performer.  About 8 years ago it need serious rehabilitation
(rust on the old clamps and hardware - no stainless steel in 1972 when I
put it up) and I replaced it with an Explorer.  The Explorer is not
quite as good but I am interested in VHF/UHF mostly now and so I don't
care to have such a large beam interacting with my 7 VHF/UHF/microwave
antennas.  The TH7DXX gets good reviews from those who use it.  

If I were you, I would get the TH7DXX and sell the Mosely TA-33.

73  Gene  W3ZZ

In my opinion, YES, it's worth it because of BOOM LENGTH.

The longer boom length of the TH-7 allows it to meet its gain specification
over a wider (larger) percentage of the 20 meter band.  If you are
interested in ONLY CW OR ONLY SSB, you could probably adjust the TA-33 so
that its gain was almost the same as the TH-7's gain, but it would be only
over a narrow portion of the 20 meter band.  

I have used four TA-33s and one TH-6DXX, and the TH-6DXX was by far the
better antenna.  I thought the TA-33 was more rugged and stayed together
better, but the TH-7 outperformed the TA-33 by having constant gain across
the 20 meter band.  I believe the front-to-back ratio will be better over a
wider bandwidth, too.

These issues are not as important on 15, where the amateur band is not as
wide (in percent) and may not be important on 10 meters either, depending on
whether you ever operate on the high end of 10.  

Hope this helps.


Just do it!!  You will never regret it!!
Its that simple.

Bryan W5KFT>
Hi Carlos,

I've managed to misplace my Mosley book, but here are the specs. on the

Band:                         20m                 15m              10m
<2:1VSWR           14.0 - 14.35    21.0 - 21.45  28.0 - 29.7
<1.5:1 VSWR     14.07 - 14.33  21.18 - 21.45  28.6 - 29.6
F to B (dB)              22+/-5             22+/-5            18+/-5
1/2 pwr b.w.          66 deg.           63 deg.           66 deg.
Max gain (dBi)          8.0                  8.7                  9.6

These data should line up in a 6 x 4 matrix.  If they don't, copy the matrix
to a text editor and view it there.

Just for fun, here's the TH5/MK2:

Band:                         20m                 15m              10m
<2:1VSWR           14.0 - 14.35    21.0 - 21.45  28.0 - 29.7
<1.5:1 VSWR     14.09 - 14.32  21.11 - 21.45  28.25 - 29.15
F to B (dB)              19+/-5             22+/-5            19+/-5
1/2 pwr b.w.          67 deg.           66 deg.           66 deg.
Max gain (dBi)          7.8                  8.0                  9.0

73 - JC,


If the price is good compared to new get it any way !! It is better than
the mosley. The th6dx had better front to back and forward gain, the
th7dx sacrificed all for broad band and better swr hence the two
staggered driven elements. The s model has stainless steel stuff. Much
better, old cadmium crumbled when I changed / upgraded mine from th6 to
th7. the kt34xa is better but a bear to put together and keep together.

Walt K8CV


Absolutely. It's not so much the difference in gain (there is some), 
but the difference in front-to-back is spectacular. The Mosely looks 
like a rotatable dipole in comparison.

The difference in mechanical construction is significant, as well.

73, Rod N4SI
    The DXer formerly known as N9AKE
         (c) 5 November, 1996


I have used (and still have) both a TA-33 and a TH-6.  I feel the TH-6
would definately be worth the effort to take down the TA-33 and replace
it.  You will not be sorry that you did.

Chuck, KE5FI

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