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60cm Portable AO40 rig

I am building a portable AO40 rig for use on the balcony of a condo and
other occasions where a full big-rig is not practical. I would like to use a
60cm dish I have with 2.4Ghz downlink and 23cm uplink both co-located on the
60cm dish. Size is very important here. I have some concerns and am hoping
some of you that have worked with helix feeds for dishes will advise me of
you thoughts and conclusions.

First: Has anyone placed a 3-4 turn 23cm helix feed on a 60cm dish?
Did it work?
Does one take a big gain hit from the fact that the back plane on the helix
should be about 10" in dia. (The dish is only 24") I would think you are
blocking a good portion of the reflective surface. Would the helix perform
if the back plane were not included, and merely a small impedance shim used
very near the last 1/4 turn to adjust impedance?

Second: Has anyone placed a 13cm LHCP helix inside a 23cm LHCP helix as a
dual feed system? I would assume a cavity of some sort would be necessary to
keep the 23cm out of the front-end of the 13cm downconverter. (I think I
recall someone talking about this on the bird the other night.)

Finally: Any other thought you have on such a project would be very much

Thank you in advance,

Gunther Meisse

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