Hi, TIm.
Of course, anything going through what is supposed to be a "waveguide below
cutoff" needs to be nonconductive, filtered, or grounded - which you did -- to
the chamber wall. I recall in a "former life" grounding huge disk drive data
cables with sliding plates at a cable entry panel. That said, we often
don't need what the chamber can deliver. Many emissions tests may be done if
ambients entering a chamber can be held to 6 or 10 dB below the test limit.
It's quite common, actually, to see people doing this.
Then they doubt what you tell them about backshells and filter connectors!
For some tests, ground loops are prevented with isolated feedthroughs, with
integrated planar bypasses to keep actual RF from passing the shield. I've
used a North Hills isolation transformer for others,
FWIW, and a little OT, people who think the figures in MIL-STD's and other
stadnards contain all there is to say about testing have been surprused and
horrified at some of the things that have to be done to get a good test.
(Especially if it fails!)
But that is another subject.
Cortland
KA5S
----- Original Message -----
From: Haynes, Tim (SELEX GALILEO, UK)
<mailto:[email protected]>
To: [email protected]
Sent: 1/14/2009 7:26:49 AM
Subject: RE: Anechoic Chamber: Pass-through vs. Bulkhead
...
However, it might be acceptable to use a pass-through pipe where the
pipe is
long and can provide a sufficiently high capacitance to ground to form a
functional filter at the frequencies of concern. The capacitance might be
increased by "stuffing" the pass through pipe with conductive wire wool.
I once had no option but to "pass through" a cable into the chamber. The
project allowed me to remove the outer insulation at the pass through and I
bonded the cable shield to the screened room by using a bolt to apply pressure
to a shim of metal that held the cable firmly to the metal of the pass through
pipe. That worked well.
-
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