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

To: tentec@contesting.com
Subject: Re: [TenTec] What makes the 238 good or any other tuner good?
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 19 Jan 2006 17:43:31 +0000
List-post: <mailto:tentec@contesting.com>
Thanks for the clarification Roger. It sounds as if you originally were targeting matching networks in the shack at the tx. the new class of s.s. AM broadcast tx have built in tuners to correct for variations in vswr on the lines so they can operate into < 1.2:1 and be happy.
This is partly because the tx sites are unmanned these days so there usually isn't someone immediately available to go out to the doghouse and adjust the antenna tuner to correct for changes in ground conductivity due to moisture changes and these transmitters are designed to trip into fault mode if the vswr goes above 1.2:1.


73
rob / k5uj


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

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