[asac] receiver specs

[Stephane Guilloteau]

Dear ASAC members,

    As pointed out in John's message, getting the receiver specs is
important. As usual, the sooner the better...
The parameters have different influence on the receiver design.

The polarisation purity requirement mostly influences the optics and
horn/orthomode transducer. I would assume that the 1 % goal in calibration
requires a cross-polarisation better than 20 dB, and that all antennas
should be
also co-aligned in polarisation to the same level. What do the polarisation
experts (==> Dick Crutcher) think about that ? Note that it may be difficult
to reach this level with an orthomode transducer... Can we accept lower
specs ?

The noise performance influence the mixer design and optics design. If we
fail to set agressive enough specifications, engineers may be free to select
a simpler but more noisy design... Yet we must be reasonable to avoid
throwing out all receivers... This may require a faster input than the next
face to face meeting.

I can try to draft a recommendation on the lab measuring device to evaluate
"cartridge" performance with B.Lazareff.

    Stephane