"Tom Horne" wrote in message
news:8eaZi.83$Y32.5@trnddc04...
Tom Horne wrote:
My question, again, is what measuring instruments can be effectively
applied to the comparison to provide results that will be born out by
real world performance.

Bob Bob wrote:
Hi Tom

Direct field strength measurement at the "normal" coverage distances,
calibrated and compared against a known/real world system is IMO the
best choice. I was involved in a VHF paging project that used a laptop,
GPS and measuring receiver for the job. The laptop had a A/D converter
attached to the parallel port. This gave coverage results that were
compared against a modeled prediction, but there is no reason you
couldn't set it up to compare a "new" system to an existing/real one.
One of the beauties of sampling over some time/distance is that small
positional errors with nulls/peaks evident on VHF/UHF can be averaged or
even studied as a distribution. The system I worked with you could even
see Raleigh fading on, but for us it wasn't a useful output!

Biggest hurdle is the RX. You need some kind of Volts per dBm signal
output. You could of course take an S meter output and calibrate it.

If you want a rough answer it may even be worthwhile attaching a laptop
line input to an RX audio out and doing a visual/waterfall analysis of
the level of (FM) quieting present with different antenna systems. You
could of course also calibrate this system.

If you don't want to travel to the limits of the coverage area you can
always do the tests at a lesser distance and then extrapolate with some
RF coverage software.

Hope you find this helpful. Your comments on theoretical debates are
noted, but the best you can do is to just not read them.

Bob VK2YQA

Bob
As you can see from some of the replies I gave to others I'm trying to
devise a way of practically comparing antennas available because in
emergency service communications support we have no way of knowing were we
will need to set up. Hence the desire to set up some sort of antenna
experiment that will allow us to compare the antennas against each other.

Just for the sake of my education is it likely to be true that the antenna
that puts out the most effective radiated power will be a bad choice in a
large percentage of possible sites?
--
Tom Horne, W3TDH

Hi Tom

My approach to the problem of comparing antennas to each other would
involve using satellite signals as the illuminator and build as many test
antennas as you have interest in.

For 2 meter antennas, the 137 MHz from the NOAA satellites is probably
close enough. That would require making some test antennas about 5% bigger
than the 2meter antennas.

If you E-mail me I can show you some radiation patterns I have plotted
from NOAA satellites. My plots of actual measured signal strength make me
more and more confident that EZNEC is accurate.

Jerry