# [TowerTalk] Measuring Common Mode Choke with Anritsu VNA

Máximo EA1DDO_HK1H ea1ddo at hotmail.com
Tue Jan 2 16:04:49 EST 2018

```Next picture it is more clear than previous one.

Same measurement, same choke, at same time, S11 red (Zmag), S21 blue (TL dB).

Markers show 0.9 MHz offset.

https://1drv.ms/i/s!AmG0n3993dIchj1NPdwk7pQLAVrf

________________________________
De: TowerTalk <towertalk-bounces at contesting.com> en nombre de jimlux <jimlux at earthlink.net>
Enviado: martes, 2 de enero de 2018 18:59
Para: towertalk at contesting.com
Asunto: Re: [TowerTalk] Measuring Common Mode Choke with Anritsu VNA

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
Wie misst man sehr hohe Impedanzen Ein Vergleich zwischen ...<http://hamcom.dk/VNWA/How%20to%20measure%20very%20high%20impedances-Deutsch%20DG3OK.pdf>
hamcom.dk
- 1 - Wie misst man sehr hohe Impedanzen Ein Vergleich zwischen VNWA in verschiedenen Messmodi und dem VNWA mit einem RF-IV-Adapter. Dieser Artikel wurde inspiriert ...

>>

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)
_______________________________________________

_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
TowerTalk Info Page - Contesting<http://lists.contesting.com/mailman/listinfo/towertalk>
lists.contesting.com
TowerTalk is for discussion of tower and HF antenna construction topics. TT members have lots of helpful information and are happy to share it.

```