[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

Jeff Blaine KeepWalking188 at ac0c.com
Wed Jan 3 00:59:23 EST 2018

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.


On 02-Jan-18 10:34 PM, Avery Davis wrote:
> On 1/2/2018 10:00 AM, Jim Brown <jim at 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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