[Gb-ccb] RFI screening requirements

[Martin Shepherd]

It occurs to me that I really don't know what Green Bank's RFI
screening requirements are. Discussions at different times have
implied widely differing requirements.

For example, at the preliminary design review I asked whether a
honeycomb RFI ventilation filter would be ok for the cooling fan,
given that the attenuation of this filter dropped off rapidly above
10GHz. I was told that this fan-screen would meet GB's RFI
requirements. Now however, there is concern at GB that the 2.5mm hole
in an all-metal optic-fibre feedthrough connector would not meet Green
Bank's RFI requirements. These two data-points appear to be
contradictory.

I am guessing that the difficulty in specifying this revolves around
the unknown of how much radiation a single-board computer and FPGA
will generate at microwave frequencies. I don't have the experience
necessary to make an educated guess at this, whereas I assume that
people at GB do.

So, could somebody at GB please provide me with a specification for
the cutoff frequency needed of the RFI screening?

Martin