[time-nuts] Re: Query about List and about 10 MHz Distro

[Darren Freeman]

On Sun, 2021-08-29 at 09:21 -0500, Dana Whitlow wrote:
> I believe that a significant problem in my case was not leakage
> through the
> shield, but
> rather common-mode currents on the cable.  My experiences were with
> RG-6
> style cable,

Chiming in with a maybe tangential issue.

I had some really unreliable strange behaviour in my lab, and I traced
it to some low quality BNC crimp plugs. The noise at my receiver would
fluctuate by tens of dB, as I wiggled the connector. With a good
connector, it's dead quiet all of the time.

My conclusion was that the outer conductor was not making contact when
the plug was mated with a socket, and so outer currents were flowing
through the spring, and through the part of the plug that you rotate
when locking it to the socket. That adds some impedance, and your
receiver is now also listening to the common-mode current, that should
flow harmlessly to the chassis.

Visually, you can spot these particular bad plugs from the lack of
slots in the outer conductor. There's no way for it to compress as it's
mated with the socket, so they are under-sized instead. They often feel
loose. It may work sometimes, but not with all sockets, and only if
gravity is pulling on the cable just right.

All of the ones I've received from China have been like this. They went
in the bin. The ones from Jaycar, my local electronics shop, appear to
be identical. I used them anyway, because I was travelling a lot. Since
that time, I have been cutting them off my cables, hopefully I've
gotten them all.

It's been a sad lesson. Time and money down the drain, but at least I
worked out what was going on in the end.

Maybe someone else is struggling with this issue? Try wiggling all the
connectors :)

Have fun,
Darren