New feed for LRO-H3

andrew....@googlemail.com

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Mar 19, 2026, 2:49:28 PM (20 hours ago) Mar 19

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https://www.astronomy.me.uk/changing-over-to-brian-colemans-hydrogen-line-feed-on-lro-h2-solar-cooker-radio-telescope

Alex P

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Mar 19, 2026, 2:59:17 PM (20 hours ago) Mar 19

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The positioning of that feed equates to it probably seeing ~ 30cm dia of the dish, but with the central 15-20cm or so blocked by the feed.

Alex P

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Mar 19, 2026, 3:15:26 PM (20 hours ago) Mar 19

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If this was a solar oven, how much light would be getting to the 1/4wl piece of feed wire ? " see " the problem ???

Preston Ozmar

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Mar 19, 2026, 3:46:03 PM (19 hours ago) Mar 19

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The feed does not appear to be at the focal point of the dish.

On Thu, Mar 19, 2026 at 3:15 PM 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

If this was a solar oven, how much light would be getting to the 1/4wl piece of feed wire ? " see " the problem ???

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andrew....@googlemail.com

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Mar 19, 2026, 4:51:53 PM (18 hours ago) Mar 19

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So far, I’ve only got as far as mounting it – next step is to sort out focus. Mounting it was hard enough for today!

Andy

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andrew....@googlemail.com

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Mar 19, 2026, 4:59:36 PM (18 hours ago) Mar 19

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I still have focus to sort out – today was about getting it to sit in centre of dish – a bigger task than I thought it would be.

Obstruction = (20 x 20) / (150 x 150) = 1.8% central obstruction [NB I know area has pi in the equation but pi top and bottom cancel out].

Would the best place for the focal point be just inside the bottom end of the feed?

Andy

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image001.jpg

b alex pettit jr

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Mar 19, 2026, 5:26:14 PM (17 hours ago) Mar 19

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yes. purpose of the long extension ?

Andrew Thornett

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Mar 19, 2026, 7:36:34 PM (15 hours ago) Mar 19

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Not sure - good question - ill ask Brian who made it.

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Thursday, March 19, 2026 9:26:04 PM
To: andrew.thornett via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Re: New feed for LRO-H3

yes. purpose of the long extension ?

Would the best place for the focal point be just inside the bottom end of the feed?

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Eduard Mol

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3:22 AM (7 hours ago) 3:22 AM

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Hi Andy,

Looks like you got a W2IMU type feed. I have one as well in my 3 metre dish (although it does not look as neat as yours). The main purpose of the wider section at the front is to give the antenna a narrower radiation pattern to decrease the amount of spillover noise. Indeed the focal point should be a few cm inside the opening of the feedhorn.