from K9FD
>> I had to mount the filter
>> on the copper strap that runs across the desk to ground,
from W8JI
> I know there is a popular myth, partially reinforced by
> improper instructions and articles, that filters need to be
> "grounded". Filters, if the cabling is good and the shield have
> integrity, never have to be grounded.
______________
Note that these comments are not actually in conflict. What Merv is
describing is not actually grounding, rather it is a form of shielding.
When I was in the broadcast business and had on-site transmitters, my
standard practice was to run 4" or 6" copper strap from transmitters to all
studios, and make sure all audio cabling was taped or lashed in place right
on top of the strap. The low-impedance of the strap assures that the voltage
gradient along its length is small, and the tight coupling to the wiring
effectively maintains them at the same potential. Space between the wires
and the strap does two things: it allows the higher impedance of the wiring
shields to acquire a larger potential, and it makes the system into somewhat
of a loop, which acts as an antenna.
For RF in your shack, this technique is much better place to start than
applying chokes and/or bypass capacitors. A wide strip of aluminum flashing
under or behind your operating desk can serve the same purpose -- just be
sure it continues at low impedance to the common ground where cables and
lines come indoors. (You DO have a single-point grounded cable entry, don't
you?)
73, Gary
K9AY
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