[amsat-bb] Question: small dishes for L-band uplink

[Jonathan NAYLOR <Jonathan.Naylor@xxxxxxxxxx>]

Has anyone got any experience of using small dishes for the L-band uplink ?

I currently have a spare 85cms dish which will eventually be used for 6/3cms,
but until my new feeds and tripod are ready, it is spare. I have seen lots of
documentation about using such small dishes for the AO-40 S-band downlink,
but nothing about using them for the L-band uplink.

I realise that the dish is rather small in terms of wavelengths, but putting the
numbers into the calculator gives me a gain of approximately 18 dBi assuming
a feed efficiency of 50%. On the L-band uplink I currently use a 26 element
linearly polarised yagi with approximately 16 dBi of gain. Assuming that I
feed the dish with a helix of the right size and generate circular polarisation,
I should see an impovement of around 5 dB in my uplink signal. This would be
made up from:

Gain improvement:                +2 dB
Linear to Circular polarisation: +3 dB
                                 =====
                                 +5 dB
                                 =====

Or have I missed something out in my thoughts or calculations ?

Jonathan  HB9DRD/G4KLX
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