[BC] "VSWR" Metering

[Richard Fry]

Alan Alsobrook:
>Your best results will be to sweep the line with an FDR (Frequency
>Domain Reflectometer) to do this properly you would need to
>sweep the line on commission and on regular intervals thereafter.
>If you look at Radio Guide August issue on page 26 Gary Minker
> wrote an article about this.
__________

Some network analyzers can apply FFT analysis to convert a frequency-domain 
"sweep" into a time-domain display, which is what Gary Minker was promoting 
in his RG articles.  A time-domain measurement/display is more useful in 
isolating discrete problems along the length of the transmission line, and 
separating them from the antenna reflection.

The problem remains, though, that doing this requires a lot of bandwidth. 
Gary's articles showed a frequency sweep of return loss across a 200 MHz 
span, I think, which in time-domain form showed the separate reflections at 
various transit times along the length of the system.  But the far-end 
termination of that system must have been very broadband in order to show 
the low pulse return seen in his "good system" example.

A typical sidemount FM antenna would show a very large pulse return at the 
sweep bandwidth he used, or at any other bandwidth that would be necessary 
to resolve discrete reflections along the transmission line.  So this 
technique is not useful for measuring the match of an FM antenna to the 
transmission line, i.e., the performance of the antenna, itself.

RF