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Re: [TowerTalk] CM Choke

To: towertalk@contesting.com
Subject: Re: [TowerTalk] CM Choke
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 10 Oct 2017 16:30:17 -0700
List-post: <mailto:towertalk@contesting.com>
On 10/10/2017 9:23 AM, Máximo EA1DDO_HK1H wrote:
Jim, I´ve seen someone else making a S11 measurement for CM choke?

Is that correct?
That's a reflection-based measurement, and has VERY poor accuracy when Z 
being measured is much greater than or much less than the system 
impedance (50 ohms).
http://www.lb3hc.net/archives/1358
This appears to be an S11 measurement.  The common measurement error is 
that the measured resonant frequency is much lower than the actual 
resonant frequency.
I always use S21.
This has the greatest potential for success, but it requires a load 
resistance to form a voltage divider with the choke. This is the method 
shown in that set of slides, and it correlated well with a set of round 
robin measurements done by others using classical methods (Q-meter, 
etc.). The choke being measured was wound on a material that seemed to 
be #61, thus a fairly high Q, and thus quite sensitive to measurement 
error.
73, Jim K9YC


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