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Re: [TowerTalk] use of RG11 coax - 75 ohm

To: "Ed" <sabre@magma.ca>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] use of RG11 coax - 75 ohm
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Sun, 27 Mar 2005 10:01:23 -0500
List-post: <mailto:towertalk@contesting.com>
> How does a person use the RG11 coax, 75 ohm in a ham
shack.

Ed,

You have to be careful mixing 75 ohm cable into 50 ohm
systems. Assuming you have a 50 ohm rig and antenna, the SWR
seen by the rig can range from 1:1 to just over 2:1.

Of course it can get worse than that if the system has
multiple 50 ohm and 75 ohm transitions or if the load is not
perfectly 50 ohms.

If you plan things so the 75 ohm cable is only inserted at
one point in the system and is 1/2 wl long or a multiple of
1/2 wl, things work out pretty well in most cases. Shack
jumpers are normally so short I'd use 50 ohm, but for longer
feedlines 75 is a good option.

73 Tom

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