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Re: Helix Match



 "L Clare Fowler" writes:

> I have noted with interest the discussion that has appeared re matching
> the nominal 140 ohm helix impedance to a 50 ohm line or low noise preamp.

I chickened out and took the easy route when I made a 70cm unit; I made a
second helix (6-turns, on a broom handle, in the attic), parallelled them, 
and fed with 75 ohm line. The "resistance in parallel" principle works for 
impedance too (probably throws a few snags if the units are different though).

I made the 140 ohm feedline between the two by removing the inner conductor
from some 50 ohm line and replacing it with a piece of thinner wire; the
calculations are in all good antenna theory books and don't involve much
math. Just connected the 75 ohm line to the middle of it. 

Never measured the SWR. It works. I call this practice: "amateur radio"  :))

73
Richard W L Limebear G3RWL
g3rwl@amsat.org
FOC # 1188

          So many beautiful girls ..... (sob) so little time
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