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re: AMSAT event range testing

No one else has answered this yet, and i really can't answer this one very
definitively.  Maybe someone else can, and i can learn the proper way of
doing this myself.

    Having never been to an AMSAT event (shame on me!), I was wondering if 
    someone could detail (for me or the list, take your pick) the methodology 
    and setup used in range measurements when they're offered.  Is there a 
    standardized test procedure, or at least a common set of assumptions used?
								  -- NX7U

However, i can tell you what i did to have a crude one-person do-it-
yourself antenna test range, which gave me the data i really needed to
finally get a working uplink antenna for AO-40.  SWR testing and NEC2
simulations were NOT enough to account for real-world effects in my case.

What i used was a dual-band HT with cross-band repeat, a 2M transmitter 
to activate it, and a 70cm receiver with a step-attenuator.  I also had 
the test antenna, an antenna whose characteristcs i understood, and 70cm
an quarter-wave groundplane as a reference.  (Hint:  Most full-duplex 
dual-band HTs [what you need to operate on mode J-FM] have this feature
albeit, sometimes not described in the operator's manual.  Indeed, it is 
a good indication that an HT will work properly in mode J-FM.)

I went a nearby regional park, which conveniently had a small hill about
a 1/4 mile away from a picnic table near the parking lot which faced it.
I set up the cross-band repeat with a pair of unused frequences near those
of interest on its lowest power setting and hid it in the grass on said
hill.  Then, i set up the quarter-wave groundplane as an approximation of
a reference dipole and determined the step-attenuator value which just
caused my 70cm receiver's S-meter to drop below full scale.  I wrote down
that number for future reference.  I setup my known antenna (an 'Arrow'
equivalent) where my reference antenna just was, and again determined the
step-attenuator value which just dropped below full scale.  Indeed, the
difference between those two values was close to the 7 dBd, the value i
had gotten from simulating an Arrow and my own design with NEC2.  And the
azimuth pattern was as expected.  So far so good.

I put up my circularly polarized quagi and it was all wrong.  It worked
OK in linear polarization, and even got vaguely close to my simulation,
at least in terms of pattern.  But the amount of attenuation required
got into the range were the attenuator leakage seemed significant and
things didn't appear all that linear.  Too much gain in that antenna
for this setup!  Hmmm... I retrieved my HT and went home to ponder it.

The next day, i returned with an extra attenuator, and but first, i
deliberately used a 2m rubber duck on the crossband repeat HT, to
attenuate the 70cm side at the source. (At low power, that won't hurt.)
Ah, much better...  I reproduced the Arrow-equivalent test and put on
my test antenna.  But this time, i ignored the original article's
recommendation of using a sleeve balun, and preparing just to feed it
at two corners directly.  But first, the linear test -- much better.
Now, less attenuation was needed and the value for linear polarization
was close to my NEC2 simulation.  And when i put on the circularly
polarized feed, it was indeed, 3dB lower, as expected for linear vs.
circular cross-polarization.

The next decent AO-40 pass, i finally heard myself on the downlink. (That
is, once i did the uplink frequency calculation by hand instead of using 
the spreadsheet... *sigh*).

I do not consider this to be a quantitative test, but rather a qualitative
one. The difference is not unlike the difference between using professional
equipment and a Radio Shack 2m/70cm SWR meter.  You may be able to tune an
antenna with it, but don't count on the numbers you get for more than just
a relative comparison.  Take it to weak-signal or AMSAT event to get the
real story on your antenna(s).

		         -- KD6PAG  (Networking Old-Timer, Satellite QRPer)
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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