--- Fred A Parker [email protected] wrote:
Remember this line is not designed for the high voltages you get with high
swr.
Correct.
However, trimming the line length to reduce a 50-ohm VSWR measurement in the shack does not modify the SWR on the transmission line.
To reduce the SWR on the 75-ohm line, one could adjust a yagi's gamma or delta matching network to produce a 75-ohm feedpoint impedance.
Additionally, "twelfth-wave" matching transformers (series-section transformers)
http://ourworld.compuserve.com/homepages/demerson/twelfth.htm
made from coaxial cable can be used to easily convert a 50-ohm source or load for use in a 75-ohm system.
So, you could adjust your antenna(s) for 75-ohms, and use the transformer in the shack to produce a 50-ohm load for your transceiver, while maintaining a very low VSWR on the transmission line.
You could also connect one of these transformers to the "load" (antenna) port of your 50-ohm VSWR meter to enable its use in accurately adjusting your antennas for a 75-ohm feed point impedance (1:1 VSWR).
73, de John, KD2BD
Visit John on the Web at:
http://kd2bd.ham.org/ . . . .
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