[Elecraft] K3 power reduction due to high SWR
Jim Brown
jim at audiosystemsgroup.com
Thu Apr 5 01:26:23 EDT 2012
> If I have to use your antenna, then my move would be to replace the 250'
> of75 ohm coax with 250' of 450 ohm ladder line, check the fan dipole legs
> are exactly the same to provide a balanced load.
You're on target about loss in the feedline, but ladder line is not a
good move here.David has resonant dipoles, so they are a pretty good
match to 50 or 75 ohm cable. Folks think QRP, so they think small coax,
But when the line is as long as these are, the loss certainly gets out
of hand unless it's bigger coax. If I were to make ANY change in the
feedline, it would be to a decent RG8 or RG11. I would also look at
ways to reduce the length of the line by finding a shorter route to the
shack. You don't need expensive coax -- Davis 213 is about as good as
it gets for the HF bands, and it's fairly inexpensive.
Window line is NOT the cure for all ills -- it is as lossy as small
coax when it gets wet, and there's some loss (and cost) in any impedance
transforming balun. Further, most real antennas are unbalanced by their
surroundings, so they need a good ferrite common mode choke at the
feedpoint whether they're fed by coax or parallel wire line.
73, Jim Brown K9YC
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