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Re: [TowerTalk] Measuring Common Mode Choke with Anritsu VNA

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Measuring Common Mode Choke with Anritsu VNA
From: Jeff Blaine <KeepWalking188@ac0c.com>
Date: Tue, 2 Jan 2018 23:59:23 -0600
List-post: <mailto:towertalk@contesting.com>
The issue is not the value of the actual Z.  The issue is that the reported peak Z frequency can be very far removed from the true value.  Hence the problem.  If you build a monster Z choke but it's narrow banded, then the measurement error (with respect to frequency of the peak) is important.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 02-Jan-18 10:34 PM, Avery Davis wrote:
On 1/2/2018 10:00 AM, Jim Brown <jim@audiosystemsgroup.com>:
Somehow I failed to clearly make the point that measurement errors
associated with measuring high Z chokes with S11 is NOT a relatively
small error, like 10%. It can be a VERY LARGE error, like 50-70% in
resonant frequency. Which FAILS to allow assessment of suitability for
use in a given frequency range.
Jim,

I agree the error can be very large, but whether that error is
significant depends on the application.  The Keysight charts clearly
show that using a professional-grade VNA, the S11 measurement can be
accurate up to 2,000 Ohms impedance, and that can be enough for many
common-mode choke application.  If I only need 1,000 Ohms impedance for
my application I don't care if the actual impedance is 1,000, 10,000 or
100,000 Ohms.  At the very least, the S11 Smith chart test is a good
quick sanity check that a choke is basically working.  If I need to
prove a choke has a lot more than 1,000 Ohms impedance, then I agree
that some other technique is needed, and the Keysight charts discuss
those other methods.

Again, I thank you for bringing this to my attention, prompting me to
search for impedance measuring techniques and leading me to these
Keysight charts.

73,

Avery, WB4RTP


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