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[TowerTalk] Matching 75 ohm hardline for 3 bands

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Subject: [TowerTalk] Matching 75 ohm hardline for 3 bands
From: (Dave Hachadorian)
Date: Sun, 1 Apr 2001 08:20:59 +0000

On Sat, 31 Mar 2001 00:10:55 EST writes:

> Just plug the feedpoint pigtail/rotator loop (50 ohms) in 
> the end 
> of the 75 ohm hardline and live with a little increased SWR. 

You can indeed do it this way, but the swr increase may be
enough to create problems.

This drove us nuts one time at a multiop down in Mexico.
We were feeding a TH-6 and a 40-2CD with two 75 ohm hardlines.
At the band edges, both of these antennas are about 2:1 SWR,
even with a 50 ohm line. With the 75 ohm line, the swr IN THE
SHACK varied from about 1.3:1 to about 3:1, depending on the
length of the feedline, including all the interconnecting
cables in the shack. The wattmeters were all reading crazy.
The Alpha 87 kept tripping off line. The swr bridge, located
downstream from the Alpha, looked normal. It took us a while to
figure out what was happening, and we had to add different pieces of
coax on different bands to minimize the swr presented to the Alpha.

Dave Hachadorian, K6LL
Yuma, AZ

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