Re: Supporting the dish feed


John Fell
 

Hi John,
For your example of just the feedhorn to support on the single arm it has the advantages of minimal aperture shadowing and reduced feeder run .

For feed mounted RF systems a tri-or quad allows reduced individual section arms and a closed system of forces , which will improve rigidity and resistance to windage loadings , without undue increased blockage.

Looking at the tower head I guess the dish is around 6Ft diameter and middle range F/d - using at 2.3GHz or 3.4GHz  ? 

73
John
G0API

On Tue, 23 Feb 2021 at 09:24, John Lemay <john@...> wrote:
Morning all

Supporting a dish feed - one arm, three or four ??

I've recently completed a new prime focus mesh dish. I made up the usual
four arms to make a quadruped to support the feed from the rim. But it
looked a bit tricky to adjust the feed position so temporarily I provided
instead a single support close to the axis of the dish. A simple series of
holes on this arm gave me easy options for moving the feed to and fro.

I made a small hole in the mesh next to the hub to pass the cable through.
That makes it obvious that the feed cable can be shorter than one which
follows one of four arms to the rim.

I'm happy with the mechanical side of things (such as the single arm needs
to be stiffer), but what are the pros and cons as far as RF performance is
concerned ?

TIA

John G4ZTR



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