badgerchap Posted June 9, 2012 Share Posted June 9, 2012 Picked up this thread by another user (thanks MeanEYE):and got to thinking about the feasability of an SGL user based Radio Astronomy network.The idea would be based on the principle of Very Long Baseline Interferometry, in that in order to acheive the resolution of a single extremely large radio telescope, users could link up data from small, well spread out minature dishes of their own.Discarded Sky / Polsat etc. dishes could be used as the smaller elements (I've seen these used to 'image' very large angular diameter objects like the moon and sun etc., but individually they're not high enough resolution for anything smaller), and a network set up via the tinterwebs to achieve the large dish aperture.Now theoretically, I know this can be done. It's the principle behind the SKA (Square Kilometer Array), which will, after a recent decision, be based both in Australia and South Africa.I have identified a number of things that would need to be investigated to achieve this admittedly difficult and complicated goal:-Would the size of small dishes be sufficient to form the elements of the large dish?-How many dishes and users/participants would be neccessary?-What networking would be neccessary, and how could suitable software be created to allow the dishes to communicate?-How can accurate timing be achieved (I know large scale proffessional operations employ atomic clocks to synchronise scopes - how could such a network as this achieve a suitable level of accuracy with amateur funds and abilities?)?I'm sure there are a billion other problems that would be encountered, but first things first, would anybody be interested in participating?It'd be a great way to give us all something to do when it's cloudy (so it's be well used)!I wouldn't expect any miracles with this, and it would, through neccesity, be a long term project. I may be able to get help and assistance from my University, as I am aware that at least one, but most likely several more of my lecturers are involved with Radio Astronomy, and I'm sure they would be up for giving some assistance. I may even be able to get the department to contribute in some way, whether it be with equipment, funding ar even just support. I haven't approached them with this idea, seeing as I've only just had it, but I'm confident I could at least get some advice out of them! Could also be a cheeky contribution to my degree although of course that would only be a happy by-product!So please let me know what you think. Whether you're interested in participating / contributing, or even if you just have some sage advice on whether or not this would be possible, or to point out any potential pitfalls, or to dismiss the idea entirely, please speak up! Link to comment Share on other sites More sharing options...
sologuitarist61 Posted June 9, 2012 Share Posted June 9, 2012 This is certainly an idea that could and should be pursued if anyone out there has the knowledge base so that us less knowledgable people can particpiate. How about it people, any electronics people out there who can help? Link to comment Share on other sites More sharing options...
ixalon Posted June 9, 2012 Share Posted June 9, 2012 Call me a sucker for a cool project, but I'd be interested (after moving house!)It seems possible - these guys seem to have been doing something similar http://www.eracnet.org/workshop/allbin.htm (though not sure the current state of the project - there's not much recent activity at http://tech.groups.yahoo.com/group/erac-vlbi/).Not sure how well it would work with smaller portable dishes though? Link to comment Share on other sites More sharing options...
Black Knight Posted June 9, 2012 Share Posted June 9, 2012 I think it's a great idea, although that's easy for me to say since I have no technical knowledge whatsoever! . Is it even feasible? Link to comment Share on other sites More sharing options...
Mr TamiyaCowboy Posted June 9, 2012 Share Posted June 9, 2012 i tinker with stuff, and the build would not be to hard for myself.in theory using site shown in other link, i could be up and running in under two weeks.am a dab hand at bodge jobs, and hands on modding.will keep a watch on thread. Link to comment Share on other sites More sharing options...
Gina Posted June 9, 2012 Share Posted June 9, 2012 My background is electronics. I also have some experience of mechanics, computer interfacing, programming and building the odd wooden shed I have very limited knowledge of microwave electronoics though - my fields cover lower frequencies. I used to know the physics (wave theory) but my knowledge is rather rusty. Mind you a lot of my knowledge is a bit rusty and my brain is not what it was but my enthusiasm hasn't dininished all that much Anything new I find interesting and radio astronomy is of definite interest. My experiences with Peltier coolers may be useful. I wonder just how low they will go - I've managed -22C so far and that's in the chip, I expect the cooler was lower. Link to comment Share on other sites More sharing options...
badgerchap Posted June 9, 2012 Author Share Posted June 9, 2012 Well it's great to have some interest. I guess as my degree is in Astrophysics, I should concentrate on the receiving and antenna side of things. Maybe as I learn more I can refresh you on your wave theory Gina? Anyway, seems like at least some of us might be up for it! Link to comment Share on other sites More sharing options...
badgerchap Posted June 9, 2012 Author Share Posted June 9, 2012 Sorry, just bumping x Link to comment Share on other sites More sharing options...
Vince1963 Posted June 10, 2012 Share Posted June 10, 2012 Hi Guys.. I'll be honest... I have not the faintest idea of how to go about this but i want to take part in some way, maybe the various astro clubs across the country could work together as teams this combined knowledge would help each other. and i think improve its likelihood for success PS...Will i need one of these?.....http://www.maplin.co.uk/satellite-finder-48325 Link to comment Share on other sites More sharing options...
earth titan Posted June 10, 2012 Share Posted June 10, 2012 Count me in.Mechanical engineering background here. Link to comment Share on other sites More sharing options...
jamespels Posted June 10, 2012 Share Posted June 10, 2012 Copying comments over from another thread at Badgerchap's request...Couple of questions...1. we are not all going to able to connect to the same data store at the same time (even different cable lengths to the exchange and withing the internet will be enough to knock the results out), so we will need to find a very accurate clock and include it in all signals. The only obvious thing I can think of is the GPS time signal - has a few issues but could be usable?2. alignment might be a bit of an issue. Even with a powerful, local source (the Astra satellite - does anybody else get visions of a knackered Vauxhall in geostationary orbit when they hear this?), even a very small angular error meant next to no signal. Anyone have any idea what degree of accuracy we will need or how to achieve it?On consideration last night, I have added the following...TIMING- we are not going to be able to bring signals together in real time, so the key thing is to record a very accurate clock signal. From the 'pedia article, so long as the timing signal is consistent (e.g. we don't need to know exactly which second it is, but we do need to know that one second recorded by one receiver is EXACTLY the same as one second recorded by another), we can use the time to roughly align the tracks, then fine-tune them until interference patterns emerge (this is a software issue which the OP might like to get involved in )- The European VLBI apparently uses atomic clocks synchronised against GPS; we are not going to be able to afford atomic clocks so we are going to have to use GPS alone unless anybody has a better idea. My biggest concern with this is that GPS holds a deliberate error for non-military users (this is why it is accurate to a few meters rather than centimeters); I understand the European equivalent is better? Any volunteers to look into this?ALIGNMENT- First off, if we are not looking at EXACTLY the same thing, we are not going to get a decent signal (pretty obvious, but needs stating, I think). VLBA achieves <1 milli arc sec resolution; I think a long term target of 1 arc sec resolution for us would be brilliant, with 1 arc min being a good starting point. Any thoughts on this? If these resolutions are what we aim at, then a good goto should be fine, I think.- Another one for the programmers / experienced goto users... if we have a central server with observing targets, could a local PC get these and give the goto drives the exact coordinates? I have never used one so apologies if this is obvious.More later... need to get in the garden now!. Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Excellent input there jamespels,The alignment I would have to ask someone else to answer you on that - I'm not au fait with goto so far.As for the timing, I think this could potentially be our undoing. I've tried (fairly in vain so far) to find out how precise the GPS synchronisation would be, but I can only so far see that it's at worst accurate to about 1/100th of a second which I suppose is 100Hz. I'm not sure if this is accurate enough to then allow us to fine tune? I agree about the timing consistency - i.e. it doesn't matter which second, as long as it's the right one. This could be a saving grace really. As for fine tuning software, I think there is some already available as a result of other similar projects to this, but I reckon from what I've seen they're fairly old and may need either rejuvanating or even starting from scratch. I personally dont yet possess the skills to build such a programme, but I will in time as this is part of my course. In the interim though I can probably find a willing contributer if no-one on here is up for it. Would be best to keep it SGL though, so if anyone knows how....? I also like what you said about a long term resolution target - I think that any finer than that could well be beyond our means, but as a long term goal, I think that's fairly achievable.I have managed to track down the relevant lecturer at uni concerned with RA, and thankfully he's one I have been taught by (only in mathematical methods, but that's not his prime focus!). I've not actually asked him anything yet, but I have sent an e-mail asking him if I can ask him, if you catch my drift?! Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Excellent News Earth titan - your engineering know how will be invaluable, as I struggle with anything more sturdy than sellotape and toilet roll tubes Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Hi Guys.. I'll be honest... I have not the faintest idea of how to go about this but i want to take part in some way, maybe the various astro clubs across the country could work together as teams this combined knowledge would help each other. and i think improve its likelihood for success PS...Will i need one of these?.....http://www.maplin.co.uk/satellite-finder-48325Vince, I have not the faintest idea either - but that's half the fun of it! My personal hope is that by banging our heads together we can work something out!Also, I got in trouble for bumping this thread earlier, so my apologies to all! Slap-on-the-wrist received and understood Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 From Gina:"One of the sites I looked at linked to in this thread mentioned a Euoropean setup (I think) that used Satellite TV line time-base 15.6KHz signal and PLL system to get very accurate timing. This is entirely possible and would just require a satellite TV receiver and dish to receive the TV signal - plus some home made circuitry. GPS is nowhere near accurate enough apparently" Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Found a range of dishes here:http://www.satellite....com/dishes.htma 1m dish can be got for around a hundred quid. I seem to remember reading that a 1m dish is good enough for a range of targets all by itself - obviously not for the top level stuff, but it'd be a great plaace to start, especially if it was just for working by itself. Not sure if it would be neccessary to have one this large for interferometry or not. Smaller dishes may well work for this. Large dishes are available too (up to 3m) but they begin to become prohibitively expensive!Also found an antenna maufacturer / supplier about 10 miles down the road from me Mum, so might well drop in next time I visit! Link to comment Share on other sites More sharing options...
Vince1963 Posted June 10, 2012 Share Posted June 10, 2012 Is it critical that the satellite dishes will ALL have to be the same size in the Array ?, I was hoping to do this on the cheap and i think a lot of guys on here will feel the same. A 1Mtr dish cost about £100 alone (with the LBN) were a 60cm dish cost around £35... Will it need to be mounted on a goto mount with tracking capabilities?, if so then a 1mtr dish would be too heavy (please excuse my ignorance), I have seen the 60cm dish that is made of plastic (i think its plastic) which wouldn't be heavy. Link to comment Share on other sites More sharing options...
jamespels Posted June 10, 2012 Share Posted June 10, 2012 Large dishes are available too (up to 3m) but they begin to become prohibitively expensive!I can think of other reasons they would be prohibitive, too - particularly in our house!Seriously, if we can find one supplier willing to provide discounted dishes in various sizes for the project, it won't make any difference what size each peron uses.Coming back to the GPS signal - the timing signal is apparently accurate to 4 nanoseconds (from a well-known online encyclopaedia). I like the idea of using the satellite TV clock but this would need two dishes - one pointing at the satellite and one at the target. GPS has the advantage of not being directional (though it does give multiple sources with different times, obviously!!!).J. Link to comment Share on other sites More sharing options...
JamesF Posted June 10, 2012 Share Posted June 10, 2012 Is NTP insufficiently accurate for these purposes? It does have the advantages of existing already and having suitable software available for a range of platforms.James Link to comment Share on other sites More sharing options...
jamespels Posted June 10, 2012 Share Posted June 10, 2012 Is NTP insufficiently accurate for these purposes? It does have the advantages of existing already and having suitable software available for a range of platforms.JamesSorry James, what's NTP? Link to comment Share on other sites More sharing options...
RogerTheDodger Posted June 10, 2012 Share Posted June 10, 2012 NTP suffers from propgation delay and can be tens of milliseconds out.I'd be interested in this project too, electronics and mech engineering (although I no longer have access to a mech shop) and HPC computing arrays. Link to comment Share on other sites More sharing options...
JamesF Posted June 10, 2012 Share Posted June 10, 2012 Sorry James, what's NTP?Network Time Protocolhttp://en.wikipedia.org/wiki/Network_Time_ProtocolJames Link to comment Share on other sites More sharing options...
JamesF Posted June 10, 2012 Share Posted June 10, 2012 NTP suffers from propgation delay and can be tens of milliseconds out.Depends how you do it, I think. In particular, if you run an NTP server on the system you want to be accurate and have it synchronised against multiple sources, it can work out the propagation delays and account for them.How accurate do you need it to be? If you need sub-millisecond accuracy then it's almost certainly not suitable. On the other hand, if you have a clock source that's accurate to the nanosecond, can you make inexpensive hardware that won't have propagation delays greater than that?James Link to comment Share on other sites More sharing options...
RogerTheDodger Posted June 10, 2012 Share Posted June 10, 2012 in the region of 10^-9 seconds and better... the problem is not local timing but that of sychronisation. Link to comment Share on other sites More sharing options...
garethmob Posted June 10, 2012 Share Posted June 10, 2012 i just releised i posted in the wrong thread when i meant this one, it was effectivly what hardware we would need based on what is buzing in my head at presentok so hardware wise what exactly do we needi had a look at the ittybitty scope a while ago so is the hardware going to be based on that?i would imagine we would needsky satlight dishLMB (how many outputs 2 or 4?)motor and encoders for altitudemotor and encoders for alzimauth(i have visions of wixeys and gemreds now:P)a sort of lazysusan with rail track systemnext how does the dish connect to the computer? would we need a receiver like a usb tv tuner? there is a professional one in the RA section but its expensivethe software for viewing a single dish is available at present Link to comment Share on other sites More sharing options...
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