On Tue, 2 Dec 2003 13:32:55 -0500, Joe Subich, K4IK wrote:
>I don't know that they're exactly contradictory ... network cards can
>create a "pin 1" problem. There is no shield, several wires are left
>floating and unbalanced RF is free to find its own way to a chassis
>ground through the circuitry.
Not a pin 1 problem, but a different one. The network card is balanced
with no shield. If either the driver or the input is poorly balanced,
there can be a common mode problem. Also ,some input transformers are
better than others at decoupling RF from one side to another.
Think about this. What a ferrite choke does, regardess of the form it
takes, is reduce the common mode current, and if there is a shield, it
reduces the current on the shield, which in turn reduces the coupling
to the equipment. Many years ago, I was doing a big outdoor concert in
downtown Chicago, and my very expensive condenser mics (with a pin 1
problem) were getting hit with lots of TV channel 2 (55.25 MHz pix
carrier). I reduced the current enough to get below audibility by
wrapping the mic cable several turns around the steel mic stand. Again,
square law detection was giving me enough to solve my problem that day.
Jim Brown K9YC
http://audiosystemsgroup.com
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