hf shielding-mesh
 

ml wrote:
In article ,
"Dave" wrote:

"ml" wrote in message
...
In article , Dave
wrote:

ml wrote:
hi

i have a general shielding question i realize that overall it
might be a impractical thing to build but looking at it i
wonder...

ontop of my roof is elevator room it's about 20x20

flat roof

lets suppose the motor controller throws out 1.7 to 30mhz at
s9+ (all over)

lets say i take a single 20x20 sheet of copper put it on the top
roof (assume i could ground it if need be)

lets say before i put the copper i measured s9

what shielding if any might i see "S" wise??

i understand interference would still be radiating form the rest
of the unshielded structure but wondering if measuring ontop of the
copper sheeting id' observe any attenuation?? meaning would the
signal penatrate that copper? -- and if so around how
much??(alot/very little)


tnx
I'd try bypassing and choking the wires going to the motor and the
controller.
thanks for the help Dav, i sorta feared a simple sheet wouldn't do
much but wanted to double check

seems the device does not radiate along the power lines it just
radiate s of the device itself

it's about 12x12 x12 inches or so the motor controler is inside a
tight heavey metal cabinet the only rf measured is from that
device itself

my thought is to perhaps find a way to build copper mesh 'box' i
can place over it perhaps that would do the trick? it has to be
mesh as the controller gets pretty hot and is fan cooled
galvanized 'hardware cloth' that has about 1/2" mesh is plenty good for that
and can be easily soldered.

thanks Dav, never heard of hardware cloth and wasn't really
sure what the apeture size should be but i'll give the above a try



Presuming you're having troubles at HF, almost any aperture size will
do. (the usual guideline is that the perimeter of the aperture be
wavelength)

Of course, this only applies if it's an Efield issue. And, of course,
it assumes there's no conductors penetrating your "perforated box"
(which is what the shielding screen is). Any conductor penetrating the
box needs to have filters that "short" the unwanted signals to the
"inside" of the box.

If it's the radiated magnetic field, there's a whole 'nother set of
problems you'll have to deal with.

hf shielding
 

In article ,
Jim-NN7K . wrote:

More effective to build a Faraday Cage around the elevator room
(service techs use these for RF tight enclosures).
Jim NN7K

ml wrote:
hi

i have a general shielding question i realize that overall it
might be a impractical thing to build but looking at it i wonder...

ontop of my roof is elevator room it's about 20x20

flat roof

lets suppose the motor controller throws out 1.7 to 30mhz at
s9+ (all over)

lets say i take a single 20x20 sheet of copper put it on the top
roof (assume i could ground it if need be)

lets say before i put the copper i measured s9

what shielding if any might i see "S" wise??

i understand interference would still be radiating form the rest
of the unshielded structure but wondering if measuring ontop of the
copper sheeting id' observe any attenuation?? meaning would the
signal penatrate that copper? -- and if so around how
much??(alot/very little)


tnx

wanted to thank everyone for responding and offering some tips

just a few FYI's

I doubt i could afford or be allowed to build a 'cage' around the
entire room

The motor emits to noticable noise

the motor controller in the cabinet aka magnetek600 sure does.

i would be easy i guess since it's rather small um loaf of
bread sized to build a copper mesh around it i was considering
going to a a/c place and have them do it professionally


measuring w/my ft-817 and a small hand held spectrum analyzer i
measure almost no noise along the input power lines nor any
out to the motor there is 1 sensor cable to the motor also
no noise all are run in seperate conduit

best as i can measure that is

appreciate all the help folks

hf shielding
 

(ml) wrote:
"The motor emits lo noticable noise. The motor controller in the cabinet
aka Magnetek 600 sure does."

The cabinet should be made RF tight and grounded.

A brute force pi filter, series L and shunt C on every conductor
penetrating the shielded cabinet usually solves the interference.

Best regards, Richard Harrison, KB5WZI