AO-40 "Big Dish" Project @ W0FMS (new country QTH)

September 30, 2002

This is a start to the project of putting some of my surplus big dishes (5' up to 10') on AO-40.  These dishes are all prime focus, nominal 0.3 f/d dishes +/-.

First order of business, decent patch feeds.  Ok, mounting the dish should be first, but I have to actually get the new QTH built completely!
Since we are very close to "sun outage" time in the Clarke Belt, and AO-40 hovers very close to the Clarke Belt, the next couple of weeks should tell me
if where I want to put the dish will be clear of trees for a good part of the orbit or not.  I'm afraid I'll have problems to the East....  For me 10/6 is close enough sun arc to the Clark belt to see what is shadowed and what isn't.  SO at least I should have a site survey done in a week or so

Oh, well, back to feeds....

I've tried many designs, and it appears that the G3RUH-type feed is superior to others.  Not that I don't believe that a square patch (rectangular) couldn't be made to work as well, I've just not found the magic combination.

As far as the actual G3RUH feed-- at $170 US I can't afford it.

Not wanting to re-invent to many wheels, I am relying on the research of W0LMD who has made a simplified version of the type of patch design that G3RUH
uses.  The details are on

I'm notorously bad at measuring round things, so I took a little time and came up with a CAD drawing that summarizes the dimensions from W0LMD's site.

So far I have a correctly scaled (at least on two different manufacturer's printers here) Adobe Acrobat file that contains a template for cutting and drilling the single-band  (or dual-band portion of the) 2401 MHz circular patch that Dr. Suding mentions on his site.

This is where I'm going to leave off for today, but it might be useful to the AMSAT community, so I'm posting it before I even try it.

W0LMD 2401 MHz Circular Polarized Patch Feed Template