Grant,
I am not surprised at all by the results you saw with shielded Ethernet cable.
I have at least 2 reasons for saying that.
I spent about 10 years in mil-aerospace, mostly trying to meet the EMC
requirements of MIL-STD-462F. Some of the most difficult fixes in equipment
and cabling design came from digital interfaces. Ethernet was the pits when
trying to use industry standard plastic connectors. To substantially reduce
emissions from such cabling, shielded cables are required AND the shields must
be properly terminated such that lead length of the shield termination is less
than 1/4 wavelength at the highest frequency of interest. That requires a
metal shell connector that connects to a shielded metal shell connector on the
chassis. The impedance of the total path from cable shield to chassis must be
as short and low as possible.
Second, I am the former Chair of the IEEE Working Group that revised
IEEE-STD-299 back in the mid 1990s. That document was tagged by the DoD to
replace MIL-STD-285, which was the method of measuring shielding effectiveness
of RF shielded enclosures. In the course of doing in-situ experimental
measurements in actual shielded enclosures and chambers, we learned that coax
cables that had low levels of RF leakage from their shields and/or connectors
would produce varying levels of RF around the enclosure. Those levels would
vary with frequency and distance between the "leaky" cables and the enclosure
walls or floor.
So, you are correct - use fiber optics. Otherwise, get rid of plastic
connectors and go with mil-grade metal ones.
73, Dale
WA9ENA
Retired EMC engineer, IEEE Life Member
-----Original Message-----
From: F. Grant Saviers <grants2@pacbell.net>
Sent: May 20, 2023 10:04 PM
To: rfi@contesting.com <rfi@contesting.com>
Subject: Re: [RFI] Choosing a POE in a RF-rich environment
An example of unexpected results with ethernet cables. I replaced a
unshielded CAT5 with shielded CAT6 and RFI from the new cable was substantially
higher. It was inside my steel shop/shack. Lesson: use fiber links whenever
possible.
Grant KZ1W
On Saturday, May 20, 2023 at 05:01:53 PM PDT, Greg Troxel wrote:
David Colburn writes:
> If I run lines to an outdoor camera that are outside for more than
> several feet,
>
> should I protect them with something like this?
>
> https://www.amazon.com/Tupavco-Ethernet-Protector-Gigabit-1000Mbs/dp/B00805VUD8
There's a very deep question lurking. We more or less take on faith
that cables that are outside are dangerous and ones entirely inside are
safe. But the house is often not a sealed metal box. I'd be interested
in comments from people who understand better.
But, it does make sense to me to treat the Ethernet cable to the camera
the way that code requires antenna coax to be treated, as it's not so
different from the lightning viewpoint.
73 de n1dam
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