[RFI] Choosing a POE in a RF-rich environment

[David Colburn]

OK, cool, will put that in the mix. Thanks!

On 5/21/23 2:39 AM, Dale wrote:
> 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 at pacbell.net>
> Sent: May 20, 2023 10:04 PM
> To: rfi at contesting.com <rfi at 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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