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Passing 25W DC while rejecting 4W 4-20GHz - RF Cafe Forums
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| Mike_From_Plano
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Post subject: Passing 25W DC while rejecting 4W 4-20GHz
Posted: Sun Sep 16, 2012 9:35 pm
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Joined: Mon Apr 20, 2009
2:04 pm
Posts: 14 |
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I'm attempting to power some equipment in an enclosure
that sets in an EMC test chamber.
My difficulty
is that the customer tests up to 20 GHz for RFI
and has some customers that want 20 V/m or more
of signal strength, and I'm concerned that my shielded
DC power cable will leak enough to interfere with
my own electronics.
My first thought was
to use a bias tee, but none have met the need (including
cost).
My next thought was to bring power
in through a back to back bulkhead connector, into
a shielded chamber, and run the signal through about
10 feet of RG-174 before exiting through a bulkhead
filter into the equipment chamber.
Any ideas?
Thanks,
Mike
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biff44 |
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Post subject: Re: Passing 25W DC while rejecting 4W 4-20GHz
Posted: Tue Sep 25, 2012 10:45 pm
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Joined: Wed Apr 08, 2009
11:07 am
Posts: 33 |
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That would work, assuming the lowpass filter held
in there all the way up to 20 GHz.
I would
be tempted to put some round ferrite toroids along
the outside of the coax cable--just to keep any
standing waves down. If there is a big standing
wave, then you could get leakage thru the ground
braid at the E field maximum points. The ferrite
toroids would de-Q the outside braid so the standing
wave would be small.
If you still had leakage,
and needed to add another lowpass filter outside
of the chamber, that is where it gets dicey. Since
the lowpass filters are totally reflective, if you
have two of them at either ends of the cable, you
can make a resonant circuit out of the whole mess
and lose your rejection. A standard fix is to add
a few dB of attenuator pad at the outside LPF, but
that would screw up your passing of DC.
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Posted 11/12/2012
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