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

[Bob kb8tq]

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 <darren at 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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