[TowerTalk] Baluns/tutorial/notes.

[Steve Hunt]

Jim,

Instruments like the AIM attempt to "calibrate out" the fixture. You 
show the instrument a short-circuit, an open-circuit, and a known load, 
right at the measurement plane. It can then remove the effects of the 
fixture for unknown impedances connected at the measurement plane. I 
maintain a set of calibration files for my various test fixtures.

As I said earlier I tried measuring a 10k resistor ; I also just tried 
measuring a 10k resistor in parallel with a 3.3pF capacitor. Over the 
range 1-50MHz the results seemed plenty accurate enough for making CM 
impedance measurements on chokes.

I'm still puzzled why Jim (K9YC) was questioning the accuracy of the 
Balun Designs impedance data. The chart shown here:
http://www.balundesigns.com/catalog/1-1%205kw%20Choking%20Impedance.jpg
doesn't seem to contain impedances that would cause significant errors 
on the AIM.

73,
Steve G3TXQ



jimlux wrote:
> Steve,
> what about a high reactive impedance.
>
> Mostly, the problems I've had with this kind of thing have to do with 
> fixturing and/or calibrating the fixture out.  I was trying to measure 
> the Z of traps, and never did get a good fixture scheme worked out. 
> It's not like you can just take a couple banana plug clipleads..  I 
> finally decided to remain ignorant of the electrical properties of the 
> traps in a 6-BTV.