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Re: [TowerTalk] 75ohm cable

To: "Dave Tipton, W5DMT" <>
Subject: Re: [TowerTalk] 75ohm cable
From: jimlux <>
Date: Mon, 19 Jul 2010 15:58:22 -0700
List-post: <">>
Dave Tipton, W5DMT wrote:
> Back in the old days, I read and heard about the guys feeding their antennas
> with hardline by putting equal lengts of 50 Ohm cable on each end.  So, you
> have 5 feet of 213, 200 feet of hardline, 5 feet of 213.
> I've never tried it personally, but it does sound viable.

It's actually a bit more clever than that.. it's called a twelfth 
wavelength transformer.

going from Z1 to Z2, you have a twelfth wavelength of Z2, then a twelfth 
of Z1, then the Z2 for however long.

Be aware, though, that it's pretty narrow band.

I'd use one of the transmission line calculators and see if the mismatch 
at the antenna is that big a problem.  If you're running 1.5kW, I assume 
you're running an amp, if it's the usual tube type, then you can adjust 
the output for 75 ohms as easily as 50 ohms, so there's no mismatch at 
the Tx end.

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