I run up to 100 watts with no trouble. To get a good match. Put a dummy load on the end of the cable and keep trimming it say six inches at a time until you get a good match . Remember if the cable is cut to 1/4 wave length or odd multiple thereof it is the worst condition you can have. While 1/2 wave length or even multiple thereof is ideal. Or you could try and put some torrid beads on the end of it to help control the rf feedback back down the line. Remember this line is not designed for the high voltages you get with high swr.
Fred KF0AK
I run up to 100 watts with no trouble. To get a good match, Put a dummy load on the end of the cable and keep trimming it say six inches at a time until you get a good match.
I think this was for satellite work. At UHF, just 4" is a full quarter wave. SO in that case, probably better to make your trims at 1/2" or less each...
Bob
--- Fred A Parker fparker@paulbunyan.net 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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Fred A Parker -
John Magliacane -
Robert Bruninga