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Re: [Amps] Ouch - 23 Ohms ?

To: amps <>
Subject: Re: [Amps] Ouch - 23 Ohms ?
From: David Kirkby <>
Date: Sun, 11 Dec 2005 02:12:49 +0000
List-post: <>
Dan Sawyer wrote:
> Ouch. I picked a set of couplers that are apparently not 50 Ohms. They 
> appear to be 23 Ohms.
> What aspects of the construction would make a coupler 23 Ohms over 50, 
> or for that matter anything else? These are 20 db couplers so the 
> majority of power is passed straight through. How much impact would this 
> have on a 50 Ohm circuit? When I insert one in a 2 meter antenna path 
> the effect on SWR appears to be negligible.
> Thanks - Dan

Are you saying these couplers have a design impedance of 23 Ohms, or are 
you measuring 23 Ohms with a DVM or something?

If they are a transmission line of 23 Ohms inserted in a line of 50 
Ohms, they will transform the impedance to a value you can only 
calculate if you know the length and frequency. But for short lengths, 
the impedance in your system will not change much from 50 Ohms. As the 
electrical length is increased (either by increasing the frequency or 
having a physically longer coupler), the effect will be more pronounced.

But without knowing more information, in particular what makes you think 
they are 23 Ohms, then its hard to say much else.

dave k
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