TopBand: Light Dimmer Noise

[Larry Higgins]

At 08:48 PM 7/8/97 +0000, W8JI wrote:
>The reason they don't help is if you shield an antenna from the 
>time varying electric field you also shield it for any time varying 
>magnetic fields or radiation fields. All shielding does is make the 
>loop's "shield conductor" become the actual antenna, instead of the 
>stuff inside the shield. 

Tom, maybe you could shed further light on this subject.  I've been under the 
impression that a Faraday shield on a loop antenna acts as an electric field 
shield, but not a magnetic field shield, because the shield (usually) is not 
made of a magnetic material.  Also, I've worked with industrial
instrumentation 
for years, and in every installation chapter there is a caution to the user
that all control lines should not be in the same conduit with power lines,
and should be in their own STEEL conduit.  I've seen two instances where
the wisdom of this advice was proven.  In both cases, instrumentation wires
were in aluminum conduit.

We had severe a noise problem on a DC drive, due to noise on the tachometer
line. I called NQ9Q, who at that time was an RFI engineer at Zenith
Computer.  He asked what kind of conduit they were using, and when I told
him it was aluminum he asked whether I had picked up any aluminum with a
magnet lately.  We changed to steel conduit and the problem was completely
eliminated.  Also, isn't there a difference between a mu metal shield and
an aluminum foil shield?

Larry, N9DX



--
FAQ on WWW:               http://www.contesting.com/topband.html
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com