I am still using 3/4" 75 ohm hardline for the majority of my antennas.
If it is a 50 ohm antenna and convenient I will make the hardline a
multiple of a half wavelength.
Many of the antennas are designed for about 36 ohms and I step then up
to 75 ohms from the driven element to the hardline with a odd multiple
of a quarter wavelength of 50 ohm cable and then use a 12th wave
transformer in the shack.
There is nothing critical or complicated about it that I can tell. All
you have to remember for .66 VF coax is 30 inches for 15M. You can
scale that to any of the normal bands - 45 inches for 20M, 90 inches for
40M, 22.5: for 10M, etc. It is convenient to not have to worry about
the SWR changing when you change a coax length and have a good feeling
when you look at the thing with a 50 ohm analyzer.
Stan, K5GO
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