________________________________
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of
emcp...@aol.com
Sent: Wednesday, August 19, 2009 6:47 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Camera For EMI Chamber
Hello Group,
I'm looking for an EMI compliant camera for use in an EMI chamber. It
is not
possible to wire in an integrated system so I need to use the camera mounted
on a fiberglass tripod behind the antenna. I really do not need any special
zoom capability or remote control. The camera just needs to be there to give
an overall view of the chamber so the EUT and antenna can be monitored. The
camera does need to be quiet for EMI testing so we aren't taking data from the
camera all day long.
If anyone can recommend a certain camera model to use, that would be
very
helpful.
Thanks,
Tim Pierce
TAP Engineering LLC
Tim:
The ultimate shielded cameras are used on aircraft carriers to record the
landings of aircraft. These cameras are mounted on pan / tilt heads that carry
a nearly blast-proof camera housing. The camera is protected from at least 200
V/M fields over 1 MHz to 18 GHz. I guess that's a bit more than you can afford.
I regularly use a camera inside my shielded enclosure, watching military gear
get hit with 200 V/M. Most of the time, I need to get close to the EUT in
order to watch LCD's, plasma displays or arrays of LED's, so my camera get's
hit with fields almost as bad as what hits the EUT.
I used to like mounting a relatively cheap camera (with audio too) inside a
one-gallon all-metal paint can. You build a little bracket inside to mount the
camera, cut a hole in the can bottom (only need a half-inch or so) for the
camera to look through, and mount coax connectors (I solder them to the lid)
and a DC powerline filter (a hefty old one out of the junkbox, and I always
add some ferrites inside) on the can lid. Once you squeeze that lid onto the
can, you have an excellent RF shield around your cheap camera. Most room audio
propagates through the can walls pretty well, but you could always drill a
pattern of tiny holes near the camera microphone. Surprisingly, you usually
don't need any shielding over the video aperture hole, but you could always
add a patch of copper screen for good luck.
Attach two good coax cables to run to your monitor beyond the penetration,
plug in the wall-wart DC power supply, and you have a fixed focus, color video
camera with audio, proof to well over 200 V/M, all for under $50.
Since my lab, being a picturesque bat-cave, is on the executive tour route, I
had been getting some comments that my "camera in a paint can" didn't appear
to be sufficiently high-tech looking for the area. I finally discarded the
paint can, and bought a 12" x 10" x 8" rectangular aluminum project box. I did
the described installation of the camera as described for the paint can
example. I use an ancient Sony Hi-8 Handy Cam, which has an integrated
microphone and a great optical zoom. I spent more time making a set of plastic
pushrods to control the zoom than I did on anything else in this package. Once
again, I didn't use any shielding mesh on the video aperture.
I had assumed that the aluminum project box seams would be leaky, so after
assembly, I applied 1" wide aluminum tape along every seam. (I used plain old
non-conductive adhesive aluminum tape; it's a lot cheaper, and performs great
in this type of work. I think the secret is to aggressively "buff" the tape
until it intimately conforms to the metal surface. Here's a special secret
tip: Take an inch or so of the aluminum tape and stick it over the end of your
finger. The adhesive will hold it very well to your finger. Now use this
armored finger to do the buffing of the aluminum tape. This way, you don't
shred and bloody your finger on those razor-sharp tape edges. And the
tape-on-tape interface is low friction, so it makes the task a lot easier.)
And the results? Again, a great camera with superb RF shielding (and it's
quiet enough to also be inside the chamber for emission testing; BTW, I always
use a cheap brute-force linear wall-wart, never a fancy efficient switcher).
All on a petty cash budget and a few hours time.
The alternative is developing an RFQ, researching the camera market, writing a
purchase request for capital equipment, defending and advancing that request,
probably rewriting the request, and waiting a long time.
Ed Price
ed.pr...@cubic.com <blocked::mailto:ed.pr...@cubic.com> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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