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Re: [Amps] Ouch - 23 Ohms ?

To: David Kirkby <>
Subject: Re: [Amps] Ouch - 23 Ohms ?
From: Dan Sawyer <>
Date: Sun, 11 Dec 2005 08:10:17 -0800
List-post: <>
Thank you. The pickup tap reads about 23 Ohms. If I string 6 of them 
together, out to in, and terminate the last one with 50 Ohms the 
impedance is about 22 Ohms.  The only negative effect is they appear to 
take about 2 db off the signal (this is measured across a broad 
frequency range with a spectrum analyzer.)

As you said, in an antenna circuit there appears to be little or no 
effect. I am using two of these near an antenna. The first one is 
connected to pick up forward, and the second one is reversed to pick up 
reflected. They seem to work without much effect in this configuration.

Thanks - Dan

David Kirkby wrote:

>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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