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Re: [TowerTalk] T-match vs Gamma-Match Trade-off

To: 'towertalk' <>
Subject: Re: [TowerTalk] T-match vs Gamma-Match Trade-off
From: Jan Erik Holm <>
Date: Tue, 07 Dec 2004 09:21:04 +0100
List-post: <>
Agree, as I wrote in a previous post T-match sure is a lot
better from a engineering standpoint. On a performance
basis I dont think anyone can see any difference at least
not when it´s up to short yagis, i e yagis without side
However I guess my point was to point out that the gamma
match isn´t a totaly unusable thing, it didn´t seem fair
to ditch it compleatly. I still consider it to be a very
quick and simple way to feed a yagi antenna.
I have 12 HF yagis with gammas, some over 20 years old,
never had a problem. Also friends in the area got gamma
matched yagis and we never seen those problems you guys
line up.
But as I did say previously, these days I probably would
do T-match yagis instead since a gamma match isn´t a
perfectly balanced feed.

73 Jim SM2EKM

Frank Donovan wrote:

I've used gamma-matched Yagis for many years. I still have three
gamma-matched 20 meter Yagis and my remaining 18 Yagis
are T-match fed.   All have been trouble-free for over 10 years.

Over a fifteen year period, I had numerous problems running
1500 watts into gamma matched Yagis, including an incident
where a feedline on a 10 meterYagi arced to the boom about
8 feet from the driven element, a 40 meter feedline that arced
to the tower leg about 30 feet from the driven element, and at
least two capacitors that arced on the 40 meter Yagi.

A 30 second micro-burst in 1993, with winds in well excess of
120 mph, provided an opportunity (!) to rebuild 16 of my Yagis.
After the damaged antennas were removed, I discovered that
several of the still functioning gamma-matches had water in
the capacitiors, a sure indication of failures yet-to-come.

In addition to major upgrade in the mechanical strength of the
Yagis, I decided to eliminate the troublesome gamma matches.
I implemented T-matches on all of the new Yagis, because
I was convinced that they could be built in a manner that would
prevent matching network failures.  My T-matches are of
conventional design, with no capacitors, 1/2 wavelength
RG-213 baluns, with particular attention to long-term
water-proofing of all electrical connections.

An significant benefit of T-matched Yagis is that they present
a DC short circuit.  This is very beneficial for routine
maintenance checks of the Yagis feedlines, from the shack
to the T-match.  I keep records of the precise DC resistance
measurement (a fraction of an ohm) for each feedline.  Any
change in DC resistance (and the companion TDR
measurements) is a sure indicator of feedline or matching


----- Original Message ----- From: Jan Erik Holm <> To: 'towertalk' <> Sent: Sunday, December 05, 2004 2:45 AM Subject: Re: [TowerTalk] elevated short vertical dipole orquarterwave monopole?

Strange. I´ve used gamma matched yagis for 35 years
or so and also used (at times) very high power, never
had a failure or any problem with it.
Sure a gamma match isn´t a perfectly balanced feed
method but IMO it´s simple and reliable.

73 Jim SM2EKM

Tom Rauch wrote:

Hey, while we are on the subject, how about gamma matched
yagis. I have a friend who swears by using a gamma match
on his yagis with no feedline choke.

When I had a gamma matched Wilson 20M yagi, the common mode
voltage on the coax was so high the coax actually arced
between the tower leg and the coax shield. I was only using
a 4-1000A amplifier, so it isn't like I had a lot of power

That's my only experience with a gamma matched Yagi.

I'd bet the whole antenna is pretty much unbalanced.

73 Tom


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