[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

Máximo EA1DDO_HK1H ea1ddo at hotmail.com
Tue Jan 2 15:28:00 EST 2018

This Anritsu VNA can check and save S11 and S21 at same time.

So, checking a choke I´ve save the .s2p file including both S11 and S21.

This is the result:


[https://sf0edq-db3pap001.files.1drv.com/y4mhJtqNqlYj2tfWPzcRimPYv6UAXKUVvwDoT-3ko-nXkD43HrkVeY241aoJvcaFaA1T3JYeEkLzU_S4XxNdb5ZVbDMMuxcTLl-Bb53I7fMR-nUdZGfsWVIuK4jGT3ZWG7LZFms1hEIOtr0EDHb8zXhbSyvWBGPtzvoY6uXfSf2xzs] <https://1drv.ms/i/s!AmG0n3993dIchjxswg_HvXxBCA8M>

S11´s (left) and S21´s (right) curve are same, but the S11´s peak is at 2.8 Mhz, and the S21´s peak is at 3.8 MHz !!

At same time you can see the resonance point on the S11 plot (blue line).

This could be what Jim is saying, at resonance point, S11 fails in accuracy frequency.

73, Maximo

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>
- 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

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