Arecibo shutdown

You don't actually know anything about it. You have no idea if the drone would be even remotely useful.

If it was a simple matter of moving the receiving portion of the antenna, they would not have constructed such an elaborate apparatus.

It was administrated by the University of Central Florida. After the first incident their evaluators said it could continue functioning - but no repair notice was given.

After the second incident the advice became 'too dangerous to attempt repair.

You don't get a third notice. It collapsed on Tuesday.

RL

I wonder how many other expensive toys the Univ of Central Florida is currently abusing - and what others they may be planning to acquire, with their twisted priorities?

RL

Conceptually it is just a simple matter of moving the feed horn so that it stays at the focus of the object that they are tracking in the sky.

In practice that requires a 3 point suspension and some quite cunning mathematics to make it happen smoothly and accurately. They are aiming to maintain phase lock to a fraction of a wavelength.

As built originally it was designed for 430MHz. By the end of its life and after a great deal of refiguring it was being operated up to 10GHz.

Well, maybe not completely. The 'big dish' is a valley full of reflector elements, and 90% of those are untouched. It is possible, with a little effort, to clear away the debris and rebuild the dish. More expensive, would be to replace the mobile structure overhead. But, that structure might be engineered differently nowadays, from the way it was done back in the vacuum-tube era, so maybe the task of rebuild is less expensive than repair would have been.

I refer you to the previously quoted text describing "beam forming". I don't think that equates to chasing a poorly formed focal point of an off axis parabolic reflector.

"the unique beam-steering mechanism suspended high above the reflector dish allowed for a moveable focal point that could aim at different parts of the sky."

I don't know the details, but I'm pretty sure it isn't just "moving the feedhorn".

The problem here is people who think those involved must not know what they are doing and they themselves must know more. Not uncommon in this group.

Looking at the pictures from the crashed reflector, the edges are definitively not usable at 10 GHz. Perhaps the center part of the reflector was coated with more or less solid surface, so at 10 GHz the effective antenna diameter was perhaps 100 m or less.

Was the reflector parabolic or just spherical ?

Compare this with TV-satellite receiving systems capable of receiving multiple TV-satellites in multiple orbital positions by installing a separate feedhorn for each orbital position. Thus about +/-20 degree orbital positions can be handled simultaneous. The reflector is spherical so that the error for the extreme satellites is smaller on average than with a truly parabolic reflector.

Arecibo was chronically underfunded for at least 20 years, long before UCF got involved. The NSF said in 2007 that it might have to close for budgetary reasons.

UCF got called in to rescue it in 2016, but ran out of time. :(

Cheers

Phil Hobbs

On a sunny day (Wed, 2 Dec 2020 09:52:42 +0000) it happened Martin Brown wrote in :

Yes, thousands of sats, not only from Musk. OTOH I am very impressed what he has achieved and for "modern dishes" look at this teardown:

Now that is for you RF PCB designers! So basically an active? array replacing the focusing dish with LNB... flat! Also Musk will test his new starship second stage to 15 km this week I think. That dish is REALLY state of the art, you also see those flat dishes for sale now for normal geostatic satellite receivers, was considering buying one, about 1000$ for one that automatically steers to satellites, like this:

On a sunny day (Wed, 2 Dec 2020 06:13:19 -0800 (PST)) it happened Rick C wrote in :

Well since I modified the hardware and wrote the soft to control the drone I do about that. and I have quite some experience using satellites and dishes. So what's your experience with any of those?

You are just trolling,

On a sunny day (Wed, 02 Dec 2020 09:43:48 -0500) it happened legg wrote in :

Ok maybe it will end up like the pyramids as a tourist attraction?

Not trolling, just calling BS. I know that beam forming involves a lot more than just moving your receiver.

You may know lots about drones, but you seem to not know much about beam forming.

I refer you to the various references that I have already posted. The main dish is spherical and there are aspherical off axis Gregorian reflectors inside the radome that bring the raw beam to a precise focus.

You don't have to take my word for it:

The sky moves so to observe an object they have to track their target. Likewise when they are a node in VLBI - where their big dish provided excellent signal to noise on faint sources but they have a limited time on track. This is the guide for observers wanting to apply for time to do VLBI - its tracking range is rather restrictive with declination.

I am not sure if they ever did drift scans since the early days.

Most of it is about precise tracking in terms of a single observation. The tracking movement is typically precomputed and run from tapes on these older instruments. Though they may now do it from solid state.

Between observations they can change which front end receiver antenna is actually at the focus. They have ~5" arc pointing accuracy.

You are talking to a former radio astronomer. Although I did very little observational work with big single dishes I do know people who did.

On a sunny day (Wed, 2 Dec 2020 22:31:04 -0800 (PST)) it happened Rick C wrote in :

Since I designed my first video camera in 1967-1968 and that involves optics and making a beam is no different for light or lower frequency EM radiation I call your expertise on that bluff. In 1968 when I started working for the national TV network we got 6 month in the school benches training, one of the subjects was satellites, expert came over specially for those lessons. Later .... (as the miller told his tale) I worked for a very large company that made communication equipment where I had to write the service docs for the traveling wave amplifiers for their dishes from the lab reports. When I was captured by the flying cup and saucer the aliens .. better not talk about it, so beware, do not mess with those!

Poor Collins. As some indie song I recall says, "...they become what they deplore."

Cheers

Phil Hobbs

So it is not just a matter of moving the receiving element to obtain a prop er focus. Focusing requires elements that are far too cumbersome to hang off a drone?

You seem to be focusing on the tracking rather than the focusing that I was addressing.

I'm surprised you contradicted yourself then. You said it is just a matter of moving the feedhorn and then talk about "Gregorian reflectors inside t he radome". The context of my statements were about the idea of suspendin g all this from a drone. Clearly not practical. I guess technically you did say "Conceptually" it was about moving the feedhorn, so "technically" n ot in contradiction of using a drone.

"No different" conceptually, but the practical differences make using a drone at Arecibo an absurd idea. Did your experience teach you anything about practicality?

I don't get why you are continuing to support your clearly absurd suggestion.

On a sunny day (Thu, 3 Dec 2020 09:14:21 -0800 (PST)) it happened Rick C wrote in :

humans could not fly as those were heavier than air as opposed to birds that were clearly lighter than air, You better address the solutions and not your vague illusions of what you think the problem is. For the rest arguing with na sayers and trolls is a waste of time I see I already had you in the kill file, but you changed name again. plonk

eam forming.

optics

ation

drone at Arecibo an absurd idea. Did your experience

tion.

hat were clearly lighter than air,

think the problem is.

And yet you felt the need to share. Thank you for sharing.

Rather that display your emotions, you could just discuss the facts. The b ottom line is you can't realistically suspend the receiving elements of the Arecibo antenna using a drone. This is not remotely like a light beam or other EM phenomena because of practical issues. Theory and practice are th e same in theory. In practice they differ considerably.