Whether to terminate IC shield to ground with a Cap or not? - Tony Montana

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Technical and scientific discussion of amps, cables and other topics.

Whether to terminate IC shield to ground with a Cap or not?

Posted by Tony Montana (A) on October 20, 2004 at 15:30:13

This post refer to unbalance RCA connection, with twisted pair IC and a shield over it.

This pertain to Jon's post stating that if a cable's shield don't carry any [signal] current, it will do its job better as shield. That is why he recommend that only one end of shield on a twisted pair IC be hard wired to ground, and the other end terminated with 0.01 uf capacitor to ground (as to prevent signal current from flowing in the shield).

This will allow higher frequency [induced EMI] current such as RF flowing in the shield due to low reactance of Cap at higher frequency, but will prevent induced lower frequency EMI current to flow in the shield due to high reactance of caps at lower frequency.

My argument was that if the shield is not hard wired to ground at both ends, the shield will not be as effective on lower frequency such as 60 Hz EMI. But he said that not true.

So instead of bring up more links to argue about, I went to basic principle of shielding to tackle this problem.

The principle of shielding state:

"To provide effective protection, induced current (caused by EMI) must be permitted to flow in the cable shielding to oppose EMI. Sheath current flow produces an electromagnetic field that "bucks" and opposes the problem EMI, thereby minimizing its harmful effects and avoiding interference of communications signals.

However, by leaving one end of the shielding ungrounded to fix ground loops, a new problem rears its ugly head. When the shielding is bonded to equipment at only one end, induced currents are prevented, which eliminates the EMI protection and prevents the cable shielding from doing its job."

So Jon, there you have it :)

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Topic - Whether to terminate IC shield to ground with a Cap or not? - Tony Montana 15:30:13 10/20/04 (14)

Re: Whether to terminate IC shield to ground with a Cap or not? - Jon Risch 18:00:05 10/21/04 (9)

Where is Jneutron when we need him :) - Tony Montana 19:54:25 10/21/04 (8)

Re: Where is Jneutron when we need him :) - jneutron 11:20:54 10/25/04 (2)

Speaking of the devil :) - Tony Montana 21:56:00 10/25/04 (1)

Re: Speaking of the devil :) - jneutron 07:11:16 10/26/04 (0)

Re: Where is Jneutron when we need him :) - Jon Risch 21:14:08 10/21/04 (4)

PS - Jon Risch 21:29:09 10/21/04 (3)

Maybe you should have e-mailed Kurt. - jneutron 11:13:27 10/25/04 (2)

Re: Maybe you should have e-mailed Kurt. - Tony Montana 22:06:27 10/25/04 (1)

Re: Maybe you should have e-mailed Kurt. - jneutron 07:29:41 10/26/04 (0)

Re: Whether to terminate IC shield to ground with a Cap or not? - blackrock john 09:04:52 10/21/04 (0)

Re: Whether to terminate IC shield to ground with a Cap or not? - Top Jimmy 23:49:45 10/20/04 (2)

Re: Whether to terminate IC shield to ground with a Cap or not? - Tony Montana 20:03:10 10/21/04 (1)

Re: Whether to terminate IC shield to ground with a Cap or not? - Jon Risch 21:21:36 10/21/04 (0)

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