TopBand: Re: Measuring impedances through a filter

[Tom Rauch]

> Date:          Wed, 24 Jun 1998 22:00:28 +1000
> From:          P & V Nesbit <pnesbit@melbpc.org.au>
> Subject:       TopBand: Re: Measuring impedances through a filter
> To:            topband@contesting.com

Hi Peter,

> 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.

Maybe not, it depends on the filters loss, numb4er of sections, slope 
of the filter,  and component tolerences. I don't want to "go there" 
on the topband reflector because it would take a good sized page to 
cover all the theory.

Results could be pretty far off in some cases, especially when a 
multi-section filter will small cheap components is used close to its 
cutoff frequency.

If this method is used, be SURE to verify the results with a dummy 
load of the same impedance you calculate for the antenna. 
   
73, Tom W8JI
w8ji.tom@MCIONE.com

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