"ml" wrote in message
...
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)

First, please know that a mesh is nearly as effective as a sheet -- and
much, much less expensive. I doubt you can afford that copper sheeting.
Can you cover the roof with metal mesh? (Using this principle, I draped some
hardware cloth over my sprinkler valves & wiring and it stopped the false
triggering of the solenoid valves from my 40m antenna. Effectiveness will
vary, depending on the coupling mechanism; coupling via the building wiring
may be as much of a problem as the radiation effects.)

Unless you are creating a true RF-tight enclosure (100dB of shielding
effectiveness is typical for them.) nobody can tell you how much suppression
you'll get, since the situation affects the numbers.

Getting into a struggle with a building owner, especially if it's your
landlord, may be a bad idea. However, he is legally not allowed to operate
a serious interference source and maybe can be forced to suppress the EMI at
the source. Our local power company, bless their hearts, came out and
completely fixed some power line EMI I had a few months ago. They
appreciate the interference laws but not everybody does.