[TowerTalk] CM Choke

[Máximo EA1DDO_HK1H]

Hi Jim,


I've been using that fixture, with a voltage divider, when measure CMRR over a 4:1 Guanella, so I can try again for CM over a choke.

This is the adaptor used, with SMD resistors;


http://www.puertobalsillas.com/radio/Balun_Guanella_4_1/Sonda_RF.jpg


[http://www.puertobalsillas.com/radio/Balun_Guanella_4_1/Sonda_RF.jpg]


I know, it can be done better...


Thank you very much


73, Maximo




________________________________
De: TowerTalk <towertalk-bounces at contesting.com> en nombre de Jim Brown <jim at audiosystemsgroup.com>
Enviado: martes, 10 de octubre de 2017 23:30
Para: towertalk at contesting.com
Asunto: Re: [TowerTalk] CM Choke

On 10/10/2017 9:23 AM, Máximo EA1DDO_HK1H wrote:
> Jim, I´ve seen someone else making a S11 measurement for CM choke?
>
> Is that correct?

That's a reflection-based measurement, and has VERY poor accuracy when Z
being measured is much greater than or much less than the system
impedance (50 ohms).

> http://www.lb3hc.net/archives/1358

This appears to be an S11 measurement.  The common measurement error is
that the measured resonant frequency is much lower than the actual
resonant frequency.

> I always use S21.

This has the greatest potential for success, but it requires a load
resistance to form a voltage divider with the choke. This is the method
shown in that set of slides, and it correlated well with a set of round
robin measurements done by others using classical methods (Q-meter,
etc.). The choke being measured was wound on a material that seemed to
be #61, thus a fairly high Q, and thus quite sensitive to measurement
error.

73, Jim K9YC


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