Does your groung screen lay on top of soil? If so, could the soil have
changed......wetter......drier...etc.
================================================
"WOODS, RICHARD" <wo...@sensormatic.com> on 07/22/99 07:46:05 AM
Please respond to "WOODS, RICHARD" <wo...@sensormatic.com>
To: "'emc-pstc'" <emc-p...@majordomo.ieee.org>
cc: (bcc: Robert E. Heller/US-Corporate/3M/US)
Subject: RE: NSA
Here is our present status. We added ground screen across the table and
soldered it down. We now pass 3m horizontal by a fraction of a dB, but
vertical is out over a dB. When we moved the receive antenna out to 10m we
passed vertical! We are using tuned dipoles and have shown that they are
balanced by rotating them 180 degrees. They were recently calibrated by the
same lab we used last year. The sum of the antenna factors drifted by only
about 0.5 dB, but our NSA has moved lower by several dB. So it appears that
we can rule out antenna calibration and balance. Oh, and yes we have
ferrites on the transmit cable and we have 10 dB pads at the antennas. The
surface of our turntable is about 2 cm above the surface of the pad. Our
brushes are mounted on the side of the table and brush against the top
surface of the ring. I have noticed some rippling in our ground screen.
Could these surface variations be a problem? As I indicated before, the
site
passed its tests over the last four years. Any other suggestions.
----------
From: WOODS, RICHARD
Sent: Friday, July 16, 1999 5:20 PM
To: 'emc-pstc'
Subject: RE: NSA
We have a 10m site, but because of high ambients, we calibrate and
test at 3m. So, we have a very large ground screen for a 3m site. When we
place the transmitter on the table, we fail NSA. When we move the
transmitter onto the ground screen we pass. We can place the transmitter to
the side of the table on in front of the table as pass. Therefore, I
conclude that we are not experiencing reflections from objects near the
OATS, nor do we have problems with the screen or its connection to earth.
The antenna and cable setup also appears to be correct since we can pass
off
the table. It appears that our 1.5m table is the only unknown. We did find
that the continuity between the ring and the screen (a bolted pressure
connection) had deteriorated significantly. That is why we added the copper
straps as a more permanent connection method. There are eight short, wide
copper straps around the 1.5m table.
----------
From: b...@anritsu.com [SMTP:b...@anritsu.com]
Sent: Friday, July 16, 1999 4:00 PM
To: WOODS,RICHARD; "INTERNET[
<emc-p...@ieee.org>]"@anritsu.com
Subject: re: NSA
Richard,
Can you detail your procedure to the conclution: "The
problem appears to be
the turn table" ?
Barry
-------------
Original Text
From: "WOODS, RICHARD" <wo...@sensormatic.com>, on 7/16/99
12:28 PM:
Argh! For the first time in five years, our NSA is out of
spec on our 3
meter OATS at 30 MHz. The problem appears to be the turn
table. We can move
the equipment off of the table to one side or toward the
front and comply,
so it does not appear to be an off site reflection problem.
We have
replaced
marginal brushes from the table to the ring and we have
added wide copper
ground strips from the ring (attached with screws) to the
ground screen
(soldered). Still won't pass. Suggestions?
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