[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

[jimlux]

On 1/2/18 9:58 AM, Jim Brown wrote:
> Hewlett Packard''s app note on this topic is well known, and my own 
> attempts at measuring high values of Z using S11 resulted in large errors.
> 
> 73, Jim
> 
> On 1/2/2018 5:28 AM, Wes Stewart wrote:
>> You keep saying that and I keep directing you to Kurt's paper that 
>> shows this is incorrect.
>>
>> http://hamcom.dk/VNWA/How%20to%20measure%20very%20high%20impedances-Deutsch%20DG3OK.pdf 
>>



if you're measuring 500 ohms (10:1) a 1% error in the voltage reflection 
coefficient is a 5% error in the resistance.  1% is 0.09 dB


It gets worse:

950 ohms is 10.4%

2450 ohms is 32.2%

4.95k ohms you get 100% error if the VNA is 0.1dB (which is a typical 
number)