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Use a SGC 230 antenna analyser or similar reading SWR. Short out the ground on one the feed side of the choke to the center "hot" on the antenna side. Measure the SWR. Basically:


(Courtesy of Steve Hunt, G3TXQ)


Choking impedance = 100 Ohms, SWR = 1.5:1

Choking impedance = 250 Ohms, SWR = 1.2:1

Choking impedance = 500 Ohms, SWR = 1.1:1

Choking impedance = 1k Ohms, SWR = 1.05:1

Choking impedance = 2k Ohms, SWR = 1.02:1


If you are using an air cooled dummy load built into a large metal box such as one that is part of a MFJ tuner, your readings could be skewed by capacitive coupling to ground. Best to use two 100 Ohm non-inductive resistors in parallel across the load or an oil cooled dummy load.


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