In a message dated 3/31/01 8:16:20 AM Pacific Standard Time,
n4zr@contesting.com writes:
<< t 05:11 AM 3/31/01 -0500, Tom Rauch wrote:
>> Is there a solution for matching 75 ohm hard-line to a triband
>> antenna?...
>1.) Pick a length of 75 ohm cable that does not result in the worse
>impedance showing up at the 50 ohm cable connection point at the
>transmitter end.
>
am I right in thinking that the general answer would be to make the 75-ohm
feedline a multiple of a half-wavelength at the lowest operating frequency,
and that the worst situation would be if the 75-ohm were an odd number of
quarter-wavelengths?
73, Pete N4ZR
Contesting is!
>>
Yes. 1/4 wave multiples would give 100 ohms and the feedline would be a 1/4
wave multiple only on one band. For .66 coax 91' 2" is a 1/2 wave or
multiple on all bands based on multiples of 3.562 MHz. Better yet adjust the
matching device on the antenna (like hair pins or Gamma/T's for 75 ohms for
1:1 SWR all the way to the shack and massage the inductance in the pi net to
favor 75 ohms for max output/efficiency of the final. Or use a tuner in the
shack which most 50 ohm rigs have. K7GCO
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