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Testing RF Choke self resonance with a non-MFJ-259 analyzer!

Oct 18th 2012, 16:54

WB2LCW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I wanted to check some Radio Shack RF Chokes for self resonance!
I do not have a MFJ-259B analyzer. But I do have a MFJ-109.
I made a short coax cable with a 50 ohm resistor in series with the aligator clip on the center conductor! i have a short lead on the shield
with another aligator clip. When I test a choke I do see a abrupt drop in SWR, at certain frequencies! I am assuming that these frequency points are where the impedance of the choke has dropped considerably are the frequencies I should avoid if I am to use this choke?

Is my method correct?

73 mike
Oct 19th 2012, 19:56

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Hi Mike,

You have the right idea--those are the points where the impedance is considerably less. You do have to be careful in that those points can be moved by the environment or surroundings around the coil.

Zack Lau W1VT
ARRL Senior Lab Engineer

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