Hey: Don't forget that the cable itself is noisy when moved. Especially
Teflon insulation.
Don
On 2021-08-30 06:51, Bob kb8tq wrote:
Hi
This sort of trouble with BNC’s has been going on a lot longer
than they have been coming in from China. A lot of folks use
them *way* past the point they should. They do indeed wear
out. They also come loose on the cable.
We went a bit nuts “killing off” all the BNC cables in the area
back in …errr … 1976. The result was a significant bump in the
supples budget that month and the elimination of a whole bunch
of problems on a number of tests. Back in that era Motorola
could afford to buy / fab a few cables.
Did the saved labor hours justify the expense? We claimed it
did……It most certainly made life easier.
Bob
On Aug 30, 2021, at 1:26 AM, Darren Freeman
<dar...@freemaninstruments.com> wrote:
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
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------------
The whole world is a straight man.
----------------------
Dr. Don Latham AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304
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