[Moon-Net] 23cm small dish feed idea

Bob Atkins ka1gt at hotmail.com
Tue Nov 29 02:54:25 CET 2016

Bob Atkins has shared a?OneDrive?file with you. To view it, click the image below.


My only experience with the "Penny" feed was at 10GHz. It works and it's easy and convenient, but as I recall, it's not very efficient, especially if the F/d ratio of the dish is >0.4. It words pretty well for focal plane dished (F/d = 0.25) thought, which most feeds don't.

There are a couple of other waveguide based backfire feeds in RSGB publictions of the same vintage (see RSGB VHF/UHF manual, 3rd Edition, 1976), There's a dipole feed, again most useful with small F/d dished (0.25-0.35). There's also a back feed better matched to longer F/d dishes (see attacked file).

They all look much more suitable (or exclusively) for linear polarization.

I'm also considering a small dish for 1296, so the subject of feeds is of some interest to me. I'm assuming a septum feed with cables, preamp etc. sticking out in front of the dish will be the only reasonable way to get an efficient circular polarized feed. If there is an alternative I'd be interested!



From: moon-net-bounces at mailman.pe1itr.com <moon-net-bounces at mailman.pe1itr.com> on behalf of Alan Beard <beardal at unixservice.com.au>
Sent: Monday, November 28, 2016 3:33 PM
To: moon-net at mailman.pe1itr.com
Subject: [Moon-Net] 23cm small dish feed idea

Hi all,
With my 2m prime focus dish, I'm not that keen on a septum waveguide feed,
sticking out from the feed point, some 60cm and pre-amps and cables etc. etc..

This "Penny Feed" idea brings the feed back into the dish centre, a dead area
usually blocked by the feed anyway. Short cables can then go through my dish
centre, reducing messy cables enormously. I can even replace the feed struts
with fiberglass rods.

My question is, can the waveguide here (below) be square (or round) as with
a septum circular polarised feed?
(slots on all sides)
(Can someone model this please?)

From: http://www.microwave-museum.org/exhibits/mwm0024.htm


73 Alan VK2ZIW

Evil flourishes when good men do nothing.
Alan Beard               Unix Support Technician from 1984 to today

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