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Re: Topband: Antenna matching question

To: "Bill Wichers" <billw@waveform.net>, <topband@contesting.com>
Subject: Re: Topband: Antenna matching question
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Tue, 18 Mar 2014 17:33:22 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
You mention keeping the highest impedance part "clean" electrically, which would make me think putting the small coil nearest the anteanna would be best. Whichever part of the inductor is shunted out is essentially just adding stray capacitance, that keeps the shorted turns part of the inductors towards the feedline. Since most or all of the large inductor will be shorted out when on 40M, it will act essentially as extra capacitance in the matching network on that band.>>>>>

That's why tank systems in amplifiers have the ten meter coil near the high impedance end.

If this is only 160-40 you probably won't have a series resonance issue with unused turns, but if you cover a wide range you will want to progressively short the large coil taps. This is why band switches that do not short (like the old National amp) and why large roller inductors mess up on higher bands.

160-40 is less of an issue than 80 or 160 through 10.

73 Tom



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