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Giftmacher

Offset fed dish to prime focus

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Got 1m dish antenna, is it worth converting it to prime focus? I'm planning to put it on AZ-EQ6 mount and try reception of Hydrogen line and GOES satellites.

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3 hours ago, Giftmacher said:

Got 1m dish antenna, is it worth converting it to prime focus? I'm planning to put it on AZ-EQ6 mount and try reception of Hydrogen line and GOES satellites.

The offset feed (of your title) is at prime focus already.

The dish will be an offset segment of a parabola (hopefully a parabola) - you will need a hammer to make it into a symmetrical (coaxial collinear whatever if you like  - I need a blackboard :) )  fed dish.

It would only be a secondary focus if there was an intermediary surface/reflector, such as in a Cassegrain which would entail a hole in the middle of your dish.

Is this a language misunderstanding between us ?

Your post is a little short on detail,  and there is a vast difference between the requirements of GEOS and 21cmH :(

Edited by SilverAstro

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I don't think we understand each other. Prime focus-fed antenna I mean front-fed. Offset antenna has feeder off-axis.

From what I saw the setup for H line and GOES is almost same- two low noise amplifiers, one band pass filter. The rest in case of GOES does PC with decoder (see herehttp://www.teske.net.br/lucas/2016/10/goes-satellite-hunt-part-1-antenna-system/) Of course feeder and BPF must be tuned to another frequency (1690 MHz in case of GOES) and of course 1m dish is way too small for serious results, but I want to try it and maybe to turn my antenna to front-fed for better targeting.

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On 1/25/2018 at 07:17, Giftmacher said:

I don't think we understand each other.

Prime focus-fed antenna I mean front-fed. Offset antenna has feeder off-axis.

and of course 1m dish is way too small for serious results, but I want to try

 

Perhaps we dont ! Let's have another go :) :-

The profile of the dish is different for the different offsets. I think your meaning of "front fed" is the vertical feed arrow pointing at the dish 'V'.  You can think of that as an offset zero in which the feed is pointing along the axis.

in the case of the offset dish 1, the feed is still at prime focus, and on the axis, but looking sideways.   Similar for offset dish 3

OffSet.jpg.6973566c08c5c2d3bbecfaeff75c4f77.jpg

(diagram borrowed and modified from wiki, my yellow and green)

Edited by SilverAstro

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