On Thu, 24 Jan 2008 22:15:34 -0600, Harold Smith wrote:
>Jim: MFJ makes a filter for the 259 and etc.
>I believe that it must be a series resonate circuit across the input,
>tunable to the interfering stations freq. Z=0.
Careful! First, the impedance of a series resonant circuit isn't "zero"
at resonance, it's some "low resistance." Second, it's only "low
resistance" that frequency. At the frequency where you're measuring, it's
some value of parallel R and jX that must be subtracted (using complex
algebra) from whatever the analyzer reads. If the unknown is a fairly low
Z, that filter may fall out of the measurement, but if the unknown is a
fairly high Z, it will probably cause considerable error.
And, as W8JI has observed, reflection type analyzers are only useful at
measuring impedances within about a 5:1 (or 1:5) ratio with the line
impedance. Beyond that range, small errors in the data become increasingly
large errors in the result.
73,
Jim K9YC
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