Topband: Filters and grounding

[K9AY]

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