Re: [amsat-bb] Helix Match

[joseph v murray <k0vty@xxxxxxxx>]

Hi Richard

A question if you have time on your interesting matching of two helix.
Was the reflector a single or did both helix have separate reflectors.

Thanks

Joe Murray  K0VTY
====================

On Wed, 26 Jan 2000 18:03:51 GMT Richard@g3rwl.demon.co.uk (Richard W L
Limebear) writes:
> "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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