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Re: [TenTec] What makes the 238 good or any other tuner good?

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] What makes the 238 good or any other tuner good?
From: "Roger Borowski" <K9RB@bellsouth.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 19 Jan 2006 09:37:02 -0500
List-post: <mailto:tentec@contesting.com>
That would be a good name for them, Rob. In essence, the place to use a
matching network to avoid feedline losses is at the antenna feedpoint.
Although using an antenna tuner at the transmitter end of the feedline is
commonplace, it is not the best place to use it, just the most convenient.
As I indicated in a previous post, if one was to measure the mismatch on the
antenna side of the tuner, you can then get an idea of your feedline loss.
If in your case, your losses are as low as you say, you really don't need
the tuner as it is just allowing you to apparently tune out a relatively
minor reactance and feel better in doing so. In cases where the antenna
tuner in the shack is being used to prevent an SWR foldback of the
transceiver, allowing it to provide its full rated output power, much of
that power is being used to warm the coaxial feedline and the matching
network in the tuner instead of being transferred to the antenna to be
radiated. 73, Rog-K9RB

----- Original Message ----- 
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <tentec@contesting.com>
Sent: Thursday, January 19, 2006 8:27 AM
Subject: Re: [TenTec] What makes the 238 good or any other tuner good?


Hi Roger,

since you seem to proudly eschew the use of a tuner, I'd like to know what
you call that matching network you have at the f/p of your inverted L--a
feedpoint reactance remover maybe?

I modelled the loss on my run of 1/2" heliax to my 160 m. inverted L for a
matching network at the f/p v. if I tuned the line to 50 j0 in the shack.  I
found that if I put 1 kw into the line in the shack and had the network
tuning at the feedpoint, I'd gain a whopping 8 watts delivered to the
antenna  (well, actually 5 watts because the LC network I'm building would
dissipate 3 watts), compared to if i put the network in the shack right
after the tx.   I decided 8 watts out of 1 kw wasn't worth going outside to
the feedpoint for every qsy, or constructing a motor drive and control box
for this thing.

I don't know how many antennas are actually 50 j0 at the feedpoint in a ham
band without any coils, stubs, tuners, baluns etc. at the feedoint, but I'd
prefer to not limit myself to them and the one or few frequencies where they
are 50 j0.

73,

rob / k5uj

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