"ContestID67" wrote in message
ups.com...
I have a question for this august body.

I found a link on the 1-26 associations web site talking about the
proper length of an antenna for operation at 123.3Mhz. This turns out
to be;

1/4 wave Length: 0.61 m or 23.95 in
3/4 wave Length: 1.82 m or 71.84 in

I was curious about the length of the coax. I was under the
impression that to get the maximum power out of the antenna, that the
combined total length of the coax *AND* the antenna needs to be taken
into consideration and needs to be an even number of wavelengths.
That prevents power from reflecting at the tip of the antenna and then
back into the trasceiver. This can not only rob radiated power but
might also damage the transceiver. A VSWR meter is used to tune this
for maximum radiated power typically by adjusting the length of the
antenna.

I may be all wet on this subject as I am an electronics engineer (a
bit pusher) and not an RF electrical engineer. Any comments?


No. To get the most radiated power, the characteristic impedance of the
antenna must match the characteristic impedance of the feedline. If the two
impedances don't match, there will be a reflection of power from the ends of
the feedline, setting up standing waves.
If they're even reasonably close, the feedline length doesn't matter, other
than the slight losses from additional length.
In practice, you adjust the antenna to give a reasonably low SWR -- say,
below 1.5 to 1 or so, and you're done.
Probably more important than obsessing over SWR would be to make sure all
the connections are good, solid connections, keeping the feedline well
supported, and as short as is reasonable.

Tim Ward KD6UTW