Re: R: [amsat-bb] SWR testing of AO-40 S-band antennas

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

>From: "i8cvs" <domenico.i8cvs@tin.it>

>Hi Jason,
>
>For serious SWR measurements at 2400 MHz you need a high directivity
>directional coupler like for example an HP 11692D or similar type and a 
>very
>well calibrated  power meter like an HP 435 A
>
>You will find the theory and the basic procedure in "Fundamentals of RF and
>Microwave Power Measurements" HP Application Note 64-1A wich is free
>distributed by Hewlett Packard
>
>This HP's classic 76 pages application note on power measurements is now
>completely revised and updated.
>

Why, for amateur use of just tuning up antennas does he need a "very well 
calibrated power meter" or a "high directivity" coupler?  As long as the two 
relative readings are ok (linear)-- VSWR is a ratio--  "calibration" cancels 
out.  True if one of the readings is on the non-linear "knee" of the diode 
detector this might pose problems.

I normally just use a Boonton RF Millivoltmeter w/50 Ohm adapter that is far 
out of its range for accurate measurements at 2400 MHz, an old klystron type 
HP generator and a Narda coupler at home.  Works fine.  I've compared what 
I've done at home with the Network Analyzer here and found that this junky 
home setup is close enough for what we are doing...

True, I've gotten to do most of my 2.4 GHz tuning on the N.A. at work, but 
its just so much easier and faster.  And then I can post better results to 
my web site.  The "home setup" works just fine though.

Fred W0FMS


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