Tom Holden wrote:

I was wondering if there is a radio frequency absorptive or otherwise lossy
material with which one might line a conductive shield or use instead of it.
I have noticed when tinkering with my DX-394 receiver that when I add a
conductive shield so that it is largely enclosed there is an increase in the
coupling of spurious signals from one part of the radio to another, e.g.,
from the 455kHz IF stage into the LW internal antenna and other parts of the
input circuitry. I suppose this is because the energy that would ordinarily
escape through the plastic lid is now reflected back and is trapped inside,
thus raising the intensity. This may amount to a degradation of 3 to 6 dB.
I use galvanised steel for the shield because it is cheap, easily worked,
highly conductive and ferro-magnetic so it is a good material for keeping
out both electric and magnetic external fields. Likewise, it keeps the
internal ones in when it would be preferable to dissipate them. Any advice
on an absorptive or lossy material for use from LF to VHF?

Would a carbon spray (if there is such a thing) do the job?
How about the antistatic foam material semiconductors and other devices are
packaged in?
How thick would it have to be?

73, Tom




Carbon spray might work at microwave frequencies but I don't think it
will be thick enough
at the frequency you are working at. Tire rubber and bicycle inner tube
material works at microwave
but again I don't know about lower frequencies..

Bill K7NOM