Topband: Antenna matching question
Tom W8JI
w8ji at w8ji.com
Tue Mar 18 17:33:22 EDT 2014
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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