TopBand: Re: Measuring impedances through a filter

[P & V Nesbit]

At 09:42 23/06/1998 +0000, Tom W8JI wrote (re using a filter ahead of an
impedance analyzer):

>A bandpass filter acts like a transmission line of some 
>characteristic Zo and some length that generally changes with 
>frequency. It will not only  mess up all the readings, it will mess 
>them up different amounts on different frequencies.

Quite true, however this problem is easily resolved. Assuming the filter is
home brew, feed the component values into an analysis program like ARRL
Radio Designer, and try different terminations at the output end until you
get the same impedance at the input end as what you measured. The
termination at the output end will then be the same as the actual
terminating impedance.

Not elegant, but quick and effective.

Peter VK3APN
pnesbit@melbpc.org.au


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