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.

73,
Steve
W1KF