[RFI] Filtered connectors for video cable

Pete Smith n4zr@contesting.com
Thu, 25 Oct 2001 16:54:45 -0400

At 01:12 PM 10/25/01 -0700, Eric Gustafson guest account wrote:
>Hi Pete,
>I'd go ahead and make the sniffer...
>Are the monitor and computer powered from the same wall socket?
>The physical separation of the monitor from the computer is not a
>good idea from an RFI standpoint.  But I suspect this
>circumstance is merely making the "real" problem worse.  Ideally,
>the units should be near one another and powered from the same
>power strip to avoid efficiently coupling circulating RF currents
>into the house power wiring.
>The worst possible scenario is a large physical separation with a
>video cable whose shield integrity is not maintained and a power
>distribution system that has power arriving at the monitor via a
>separate circuit than the one by which it arrives at the computer
>(separate wall outlet is bad enough but separate circuit -

You have hit on something.  They are currently separate circuits -- don't
have to be but are now.  I can fix that.  The monitor has an AC line filter
on it -- supposedly rated for 30 dB attenuation at HF.  You'd think...
>By shield integrity, I mean that the shield fully encloses all
>the wiring all the way from (metal) panel to panel.  Connectors
>that terminate the shield to the shell by a single wire
>connection rather than having the shield bonded all the way
>around the shell (and fully enclosing all the signal wires) do
>not count.  These devices are more properly described as "antenna
>feedpoint" than as shielded connector.
>Two cables in series are a bit dangerous but not necessarily a
>fatal flaw _IF_ both cables are properly constructed as per above
>_AND_ the shield integrity is maintained where they plug together
>(and where they connect to the equipment - don't forget to
>tighten up the jack screws).
>Unforunately, many computer store aftermarket cables are not well
>constructed.  So if you do determine that you have a video cable
>shield integrity problem (using your sniffer), you will need to
>do a bit of shopping for a well made cable.  Companies like "Black
>Box" and others have the capability to make good cables and
>identify them as such.  If you have to go to that trouble, you
>may as well get a single cable that is long enough to do the job.

Yes, I'm sure you're right.  That's a good lead on Black Box.
>Most (but not all) of the cables I've gotten with monitors or
>computer systems from the big players have been correctly made.]

The monitor is a Micron, but I'm sure that the cable that makes up the
first 6 feet from the computer outward is aftermarket crud.  I'm off to
sniff the cables...

73, Pete N4ZR