[BC] "VSWR" Metering

[Alan Alsobrook]

Richard you are correct. (as usual)
I have an Anritsu site master, with it I can sweep the line and find any 
problems on it, and I can also match the antenna. You do have to set up 
the sweeps quite differently for each task.  When sweeping the line on 
commission (and on fault isolation) the line will be terminated with a 
precision 50 ohm load. To sweep an FM antenna I'm only going to sweep 
between 500 kHz to 1 MHz wide. When sweeping a line that is terminated 
into a precision load you want to sweep as wide as possible as this will 
show problems more clearly. Once the line is cleared and the antenna is 
verified everything is "closed up" and the system sweeps are done. These 
system sweeps are what you use to compare your annual sweeps to. If the 
system is already closed and you don't want to pay a climber to run up 
and tear things apart, you can take system sweeps of your (hopefully) 
properly working transmission system and use them for comparison.

My sweeper cost about $7,000, the one Gary uses IIRC is about $90,000, 
so his can do quite a bit more than mine. I'd bet if you loosened up one 
bolt on a flange he would probably see it. Elliot Klein out of Arizona 
uses a similar box to mine to do precision alignments on ERI antennas. 
He sweeps, and tells the tower guys where to move each slug, they put it 
back in and presto the antenna is perfectly tuned.



Richard Fry wrote:
> 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

-- 
Alan Alsobrook CSRE AMD CBNT
St. Augustine Fl. 32086 904-829-8885
aalso at Bellsouth.net