[Antennas] 450 Ohm Ladder Line

2002年12月11日 09:07:07 -0600

My spare antenna is fed with 450 Ohm ladder line and currently the line is 
laying
on the roof. Comparing this antenna when it was in a different location 
and the
ladder line clear of obstructions, the SWR change was minor. On 40 meters 
with the
ladder line in the clear the SWR was about 1.2 : 1 which the antenna tuner 
balanced
and with the antenna in new position and line on the roof, the SWR is measured
at about 1.8 : 1, again the tuner balances it out. The only problem is when it
rains, regardless if the ladder line is clear or on the roof as the SWR does go
about 0.3 over dry. This is not a problem as I can still work the world with
a barefoot TS-520S. Seems to me the regardless what all the programs and 
theory
has to say, ladder line in PVC or near objects is not critical. Using 
ladder line
in PVC could be helped by sealing the PVC and filling the void with 
Nitrogen gas
which would keep it dry or possibly Argon gas which will clear any moisture 
and air
from around the line. I have used both gasses when in the USAF in hard line on
high power UHF antenna systems (AN/FRT-49 - 22KW 220-300 MHz). Hope this adds
something to the thread.
73
Bob Wilder, AF2HD/AFA2HD
6032 Idlemoore Court
Theodore, AL 36582-4117
251-653-5274
http://home.earthlink.net/~bwild
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