In article , "Eike
Lantzsch, ZP6CGE" writes:

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

If you need a thicker absorbtive layer you can use the conductive
sponge which is used to pack old style DIL ICs.

I doubt that such will work below VHF. Absorbing foam polymers
have been used for decades on antenna ranges for the microwave
region. Emerson & Cuming have been making various grades of
that for a long time. Search the Web for them and see what they
say and what they have for information.

I've seen a fair amount of electronic hardware over the last half
century and haven't encountered any equipment operating below
1 GHz that used any sort of "RF-absorbing" material.

The best bet is just plain old metal shielding, bypassing feed-thrus,
series inductances, etc.

Len Anderson
retired (from regular hours) electronic engineer person