How to make metal building opaque to FM transmitter inside building?

To the radio Folks,
Thanks for the tips on using an antenna to get FM signals into my
metal building. Now, I'm contemplating sort of the opposite. Ramsey
and others sell FM transmitters. These can be connected to the sound
card in a computer. Letting a person listen to web broadcasts. One
transmitter is weak enough that FCC rules allow anyone to use one. My
brother built one and I've used it. It drifts with temperature. And my
portable radio is digitally tuned. Also, it just doesn't sound that
good. They sell another transmitter that is supposed to stay on the
set frequency. But I think the power it puts out may violate FCC rules
for me. My steel building is built on a two foot high concrete stem
wall. I am thinking that's how I get any kind of radio reception at
all inside. Before the insulation is put up if the stem wall was
covered with chicken wire would that stop my puny transmitter from
getting out and bothering the neighbors? I know, this almost sounds
like a tin foil beanie question but I'm serious.
Thank You,
Eric R Snow,
E T Precision Machine

 

Metal buildings leak RF at all seams, so your building may radiate FM
quite well. I think you can distribute low power FM throughout the
building without much far field production by connecting the
transmitter to a leaky piece of coax that is routed all around the
inside of the building. You make a coax leaky by making small
openings in the shield every foot or so. I think you want to to vary
the distance between holes so it doesn't have a periodic frequency
response. You may need to terminate the end of the line in a resistor
but if the line is lossy enough this may not make much of a
difference. Be sure to go outside with a portable radio and check for
whether the transmission is getting much past the property line.