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Re: [TowerTalk] real world formula for the length of a quarter wave tran

To: towertalk@contesting.com
Subject: Re: [TowerTalk] real world formula for the length of a quarter wave transmission line
From: Jim Lux <jimlux@earthlink.net>
Date: Thu, 14 Feb 2013 05:33:33 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 2/13/13 9:16 PM, Jim Brown wrote:
And don't forget that Vf varies a bit with frequency (it's slightly
lower at lower frquencies). The difference is small, but enough that you
want to carefully tune the stub at the frequency that you want it to
reject.  The difference is greatest on the lower ham bands, enough that
you won't get as much suppression as you expect because it's a bit off
frequency, and not big enough to matter above 20M.

More about this in my Coax and Stubs tutorial, previously cited.

73, Jim K9YC

On 2/13/2013 9:07 PM, Jim Lux wrote:

So, for a top of 75meters 1/4 wave, it would be 246*VF/4 or 61.5*VF

__

I think the OP was looking for a impedance transformer, and for that application, I think small errors in length won't have a big effect. Say you were using 1/4 wavelength of 75 ohm line to transform 50 ohms to 112.5 ohms.. If the line were 7/32 wavelength, would it be that much different?

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