Topband: Ant Analyzer Assistance request -- funky readings

[Jim Brown]

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