Re: best cable for video camera

[Andrew Burgess <aab@xxxxxxxxxxxxxxxxxx>]

>> Connecting both ends creates the potential for ground loops, which
>> can't happen if only one end is connected. Ground loops happen when
>> two different points are grounded, and you develop a voltage drop
>> across ground. Can be maddening. I've seen 20 volts difference in
>> potential on long pieces of video coax, from ground loops.
>>
>If you're having ground loop problems, by all means, try breaking the shield
>of the RCA cable connecting the two pieces of equipment. I guaranty that the
>problem will be much, much worse. For by doing so, you've now taken away the
>fairly direct signal grounding path provided by the shield and left in its
>place a lengthy run of ground wire through the building's electrical system,
>having a considerable 60Hz AC voltage differential already present along its
>length. if you want a simple demonstration of this, place a grounded sub on
>one circuit and a grounded receiver on another. Turn the sub on and adjust
>its input trim to a typical setting. Plug an RCA cable into the receiver and
>slowly plug the other end into the sub. If you have some experience
>connecting consumer audio equipment, you know what happens next: the center
>pin if the RCA makes contact before the RCA barrel, hence the shield is not
>yet connected. And should you dwell for a while with the connector partially
>mated in this manner, the resulting roar of clipped 60Hz will soon have your
>ears bleeding and/or your sub crying for mercy.

I think this will only happen if the sub does not have a 3 pin grounded power
connection. With a 2 pin ac power connection, there is only one ground, the
shield, and it must be connected, as you describe. With 3 pins there is the
potential for ground loops and the sheild need only be connected on one end.

Its also possible even with a grounded power connection that the shield isn't
connected to it inside the sub, in which case it would behave as you describe.

My sub is ungrounded ac power and howls without a shield connection :-)