On Wed, 01 Aug 2007 04:51:53 GMT, "Jerry Martes"
wrote:


"Jerry Martes" wrote in message
news:coTri.7566$yg1.763@trnddc04...
Hi Steve

It is fairly easy to record exact radiation patterns of "2 meter"
antennas at 137 MHz, using NOAA satellites at the Illuminator. If you
have any interest in the details, you can contact me anytime.
Patrik Tast developed a (free) program for me that produces elevation
plane patterns of the antenna as the NOAA satellite passes over. Since
each satellite passes over 6 or 8 times per day, decent hemispheric
patterns can be made.
I'd guess that the plot of the antenna pattern, when using Patrik's
program is more accurate than any other method when evaluating ground
based "2 meter" antennas. I am open to learning where I'm wrong about
the accuracy.

Jerry

Examples of the radiation pattern data that can be acquired with Patrik
Tast's SignalPlotter program can be seen on one of his sites
http://213.250.83.83/~patrik/apt/log...22-2007/daily/

I have used this SignalPlotter program to make radiation pattern plots by
recording rssi voltage with a simple voltmeter with a RS232 connection and
with LabJack data recorder.

Jerry


Hi Jerry,

Very good sources of information.

73's
Richard Clark, KB7QHC

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 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

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