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Re: [TowerTalk] Fwd: Fwd: Fwd: RG-149: 50 ohm/70 ohm - does it matter?

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Subject: Re: [TowerTalk] Fwd: Fwd: Fwd: RG-149: 50 ohm/70 ohm - does it matter?
From: "Paul Christensen" <w9ac@arrl.net>
Date: Mon, 16 Dec 2013 15:27:34 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
" If I recall my radio teacher, 50 ohms were decided sometimes during WW2 or even earlier. There were some switch from (I may be wrong here) from 50 to 52 ohms at one point.

Lots of folklore ranging from commonly available pipe diameters before WWII to the geometric mean of three important values: (1) Approx. 30 ohms represents a characteristic Z for optimum power; (2) 60 ohms for optimum voltage; and (2) 75 ohms represents a Z for minimal loss, all other factors being equal.

The geometric mean of 75-60-30 is 51.3 ohms and is a close approximation to either 50 or 52 ohms.

Paul, W9AC
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