On Sat, 23 May 2009 12:00:34 -0400, Joe Giacobello wrote:
>If one had to install a ground mounted vertical as far as 2,000 feet
>from the shack and wanted to avoid the expense of using low loss coax,
>could a balanced feedline be used as an alternative?
Two very important variables you haven't specified. 1) What frequency?
2) What is the antenna? Will it be matched to the line?
2,000 ft is a VERY long line for a transmitter. I just did some quick
calcs with TLW, N6BV's transmission line calculator that comes with the
ARRL Antenna Book. If you don't have that book, you definitely need to
buy it! LOTS of great info and design tools.
If you're talking a fairly tall 160M vertical, it's pretty easy to
match that to 50 ohms. 7/8 inch hardline will burn only 0.8 dB. 600 ohm
ladder line will burn 0.44 dB, PLUS whatever loss is due to mismatch
and/or whatever is lost in the antenna tuner. 1/2-inch hardline burns
1.7 dB. These numbers are for 160M, are roughly 50% greater on 80M, and
are much higher on the higher bands.
I keep hearing that hardline can be purchased from CATV companies. You
might want to pursue that option. It will be 75 ohms, but the
additional loss due to the 50/75 ohm mismatch is minimal.
Bottom line -- 2,000 ft is a VERY long run for a TX antenna. Except for
160M (and maybe 80M) antennas that are reasonably well matched to very
low loss feedline (less than 2:1), I'd explore other options.
73,
Jim K9YC
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