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Re: [TowerTalk] Tower and antenna decisions

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Tower and antenna decisions
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sat, 26 Oct 2013 21:56:29 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 10/26/2013 9:05 PM, Richard Karlquist wrote:
After considering the above, an outboard tuner looks like a much
better option.  Or use antennas that are well matched in the first
place.

Exactly right.

Two VERY important fundamental facts are that both 1) the behavior of a power stage (linearity, efficiency, gain) and 2) the response of filter networks, are exquisitely dependent upon source and load impedances. In our case, the source is the dynamic (AC) output Z of the rig (usually less than 50 ohms) and the load is the antenna as reflected by the transmission line.

We MEASURE filter networks using 50 ohm sources and terminations, but practical antennas, even with a great tuner, are at best approximations of 50 ohm loads at the TX output at the operating frequency, and are wildly different at all other frequencies, including the harmonics those filters are intended to suppress.To assume that these 50 ohm measurements represent the behavior of these rigs and filters with real antennas is total fiction.

These facts are no less true today than when I studied EE 50 years ago.

73, Jim K9YC
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