R J Carpenter wrote:

"Dave Platt" wrote in message
...

In article ,
Avery Fineman wrote:

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.

I've seen ads in an EMI-related trade magazine for a ferrite (or
ferrite-loaded polymer I suppose) material, in the form of an
adhesive-backed sheet which can be cut and then stuck onto the tops of
ICs (CPUs, DSPs) or placed between adjacent circuit boards, to help
reduce unwanted emissions. I don't know whether this stuff's useful
frequency range goes low enough for the OP's needs, but it might be
worth a look.

From my few weeks in the microwave absorber business ) , IIRC an absorber
has to be ELECTRICALLY at least nearly a quarter-wave thick to be really
good. The ferrite loading helps accomplish this. A good impedance match to
the 377 ohm impedance of free space helps avoid reflections. For a broad
band, this encourages the use of the deep pyramid absorbers to taper the
impedance mismatch.

Some hams have found that absorbing material inside to covers of preamps in
the __hundreds of MHz region___ reduces the likelihood of self oscillation.
I've never seen a serious suggestion that absorbers would help in the
few-MHz region.

73 de bob w3otc

You are right of course.
My fault. I didn't read the OP's question thoroughly enough. I was
thinking of freq. above UHF. Absorbing material for lower freq. has
to be a LOT thicker than 1 cm. This can easyly be seen in any test
chamber.
With wavelengths longer than the compartment of the circuit I do
not see the necessity of absorbing material. Common construction
practice as pointed out will be suficient. Or just bury the device
6 feet deep in the soil ;-))

Kind regards, Eike