Most all of the commercially available tuners on the market today use the
'T' match with a Balun on the output for balanced feeders. This design was
made popular by Lew McCoy in a QST article about 30 years ago. These tuners
can deal with a very wide range of impedances but is not an ideal circuit as
has been pointed out in many articles over the years. The Ten Tec 238 is
not a 'T' match but is a configurable 'L', a well proven design. That is
why I recommend it over practically every other commercially available
manual tuner for ham use. I do not use 'T' or 'L' tuners with their
toroidal baluns for balanced feeders I use a Johnson Matchbox which was
designed for that use. And yes, good commercially available tuners for
balance feeders such as the E. F. Johnson Matchboxes are getting very rare.
Reid, K7YX
-----Original Message-----
From: Sherrill WATKINS [mailto:SEWATKINS@dgs.state.va.us]
Sent: Wednesday, March 29, 2000 7:21 AM
To: tentec@contesting.com; jmlowman@ix.netcom.com
Subject: [TenTec] Re: Ten Tec antenna tuners
While I am a devoted fan of Ten Tec gear, I will not recommend their tuners
as being the "best" design for use with open wire
transmission lines. This is because it is my understanding that the design
is a basic T type L C network. This is fine for
unbalanced line but not balanced. The solution the factory uses is to
place a balun in the output of the tuner. While this may
work just fine into a perfect impediance match, it defeats the purpose of
using open wire line. That is to obtain tremendous
bandwith and very high efficiency by using a properly designed antenna
tuner that has true balanced output. An example of this
design is the old Johnson Matchbox and many examples of this type are shown
in the ARRL Antenna Book and Handbook. It is common
knowledge that high reflected power will cause an iron core balun to
"saturate" and generate heat from the precious reflected power,
thereby wasting power. A much better method for feeding open wire line is
to place the ba!
lun on the input side of the T type tuner. Why this simple solution never
occured to the factory seems odd? However, I understand
that there is one company that does make an antenna tuner with the balun on
the input side, specifically for feeding open wire line.
Seems like Ten Tec could do the same for very small, if any cost. -
Sherrill W. k4own
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