[time-nuts] Query about insulated coax panel connectors?

[Chris Caudle]

On Sat, October 24, 2020 1:24 pm, AC0XU (Jim) wrote:
> Having recently run into major ground loop noise
> issues, I have begun reworking some of my homemade
> pieces of equipment using insulated coax connectors.

There is generally a trade-off between 60Hz noise and EMI when you start
thinking about isolated coax connectors.

> Insulated BNCs are readily available.

There were BNC connectors made for telco use which have an integrated
coaxial capacitor connection to the chassis mount point.  The connector is
isolated from the chassis by a high reactance at 60-120Hz, but decreasing
impedance at RF frequencies.  I haven't looked at the info for those in a
while, not sure where the self inductance would cause the impedance to
begin rising again, but I think it was at a pretty high frequency.

> And I am not thinking about using plastic cases - that would introduce
> a whole other set of problems. I think about my lab area at work where
> a bundle of dozens of gigabit ethernet cables run through the roof directly
> over the lab bench - the ambient noise level is quite high.

If you are worried about external EMI, keep in mind that when you
disconnect the cable shield from the enclosure, you make an antenna to
pass external RF into the interior of your enclosure.  Changing to a
plastic enclosure might not be much worse from an RFI/EMI standpoint.

-- 
Chris Caudle