Steve Reinhardt wrote:
Jim Lux wrote:

Steve Reinhardt wrote:


Well, as I mentioned, this is less about an absolute antenna gain
than a figure of merit. Using a dipole as the first, reference
transmitting antenna is part of the plan. I may be crazy, but I'm not
entirely stupid ;-) (Well, maybe. Time will tell...)

You'll get strong reflections from the ground between the antennas.



Ah, yet another thing I have to consider. Since at least two of the
tested antennas will be primarily vertical, I was planning to make
the test antennas all vertical. So, I can talk myself into believing
the ground reflections are part of the real world installations, or I
can chuck it all and rely solely upon modeling. One is probably
smarter, the other more viscerally stimulating. I leave to the reader
to sort out which is which.



The tricky thing is that the reflections will have a different effect
on your reference antenna observations than on your Antenna Under Test
(AUT) measurements (consider comparing a dipole to dipole, where you
get a definite ground reflection, vs high gain dish to high gain dish)..

The way to handle this, if you've got time and inclination, is to scan
one of the antennas in height. That is, set up your AUT (or reference
dipole), then move the measurement probe vertically over a distance of
several wavelengths, making measurements at several points. From
this, you can calculate the effect of the ground reflection.

If you google: Ground Reflection Range Antenna Gain Measurement, you
might turn up something useful. It's also described in Kraus's book.

You might also want to look up the "three antenna method" which allows
you to get absolute measurements.



Jim, W6RMK

Jim,

Thanks for the leads. I will consider them. I'm also thinking of
taking a few distance measurements to see if they look like they fit
the far field 1/r*r criteria. If the measurements are too far off, then
I'll assume I've got a bad test criteria, and I'll rethink the whole
shebang.

That's the other way... make measurements at the same heights, but
moving the antennas apart... overall, you know it has to be a 1/r^2
relation, so you can fit a straight line to the bumps.


73,
Steve
W1KF