[amsat-bb] TVRO Dish Feeds - Patch vs Helix

["David Beach" <VE3STI@xxxxxx>]

I see that many hams are using 60-100 cm satellite TV dishes with homebrew
feeds for AO-40. What puzzles me are the seemingly conflicting comments
regarding patch vs. helical feeds.

I would like to try constructing a receiving dish for 2.4G using an old
offset feed dish that appears to be about 1 m in diameter. I haven't chosen
this particular dish for any reason other than it happens to be available.
If such a dish is a lousy choice, let me know!

I have read a fair bit of stuff on the net at various websites but still
have a few questions:

For this type of dish (~1 m dia, offset feed) what are the pro's and con's
of using a patch vs. helical feed? Both seem fairly easy to construct from
website pictures/instructions I have seen.

Is the f/d ratio important for choosing between these differing feeds? (I
have not measured the f/d for this dish so don't know what it is.) One
website said the ratio is important for choosing the feed type, others are
'mum' on the subject.

Does a patch or helical feed 'fit better' with a specific type of dish -
offset vs central placement of the active element?

Thanks again for your comments. I don't wish to be a pest but I have looked
already (!) and am still a bit puzzled. Good URLs would be fine if you want
to keep your reply short and the info is available but I missed it in my
searches.

David Beach
VE3STI

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