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@contesting.com> en nombre de Jim Brown
<jim@audiosystemsgroup.com>
Enviado: martes, 10 de octubre de 2017 23:30
Para: towertalk@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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