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

[djl]

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 
>> <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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------------
The whole world is a straight man.
----------------------
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304