Brings back memories! MANY moons ago, I ran an OATS in the foothills of
Colorado with lots of radio and TV ambients. Thought I'd give the two
antenna cancellation thing a quick experiment. I had one antenna on out
10 meter test mast and put a second one on the edge of our 3 meter
diameter turntable with a preamp and attenuator on one of them. With
that arrangement, I could adjust both the relative amplitude and phase
of FM and TV signals over a pretty good range, to get the best null.
After a day or so of playing around, I found that I could poke a 15-20
dB hole in some signals, but barely change some others. After
scratching my head for a while, I realized that the ones I could cancel
were almost line-of-sight from Cheyenne, and the ones I couldn't were
from Denver. The light went on. I was in a narrow mountain canyon, so
the signals from Denver had so much multi-path reflection, that whatever
one you canceled stll left three or four others with different phase
relationship. With that realization😉, I went down to Lyons and had a beer.
On 5/6/2022 1:57 AM, Bill Owsley wrote:
Tried the dual antennas to subtract out the ambients, several times
since the explanation was good.
About 20 years ago. Unsat !!!
On Monday, May 2, 2022, 02:23:26 PM EDT, Ken Javor
<[email protected]> wrote:
Likely a totally different application than yours, but a long time ago
on OATS measurements, there was development of a two-antenna test
where one was for the actual measurement, but the other was pointed
away to pick up the ambient, and the idea was to subtract the ambient
out, and leave only the EUT emissions.
It was controversial.
MIL-STD-826 (1964 – 1967) had radiated emission antenna set-up
drawings showing all antennas deployed simultaneously. In the days
when each antenna had its own receiver, if you had enough techs that
could speed up the test significantly. It should be noted that was
unique to MIL-STD-826 and it did not survive into MIL-STD-461.
I’m thinking in your specific application, the antennas should be
separated by some distance, so that they don’t affect each other. What
that separation needs to be will depend on the desired uncertainty in
the measurement.
--
Ken Javor
(256) 650-5261
*From: *Patrick <[email protected]>
*Reply-To: *Patrick <[email protected]>
*Date: *Monday, May 2, 2022 at 2:00 PM
*To: *<[email protected]>
*Subject: *[PSES] Dual antenna during RE test ?
Hi All -
I'm wondering if there is any academic or practical literature on the
use of two antennas during an emissions test. For example, research
or experiments on the use of two DRH's above 1.0 GHz, side-by-side,
one vertical, the other horizontal.
Have any researchers looked at this?
Are there any experimental studies?
Thank you.
-Patrick
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