Mr TamiyaCowboy Posted June 10, 2012 Share Posted June 10, 2012 the talking clock ? for time. or radio updated time ( weather stations etc etc)as for signal meters. maplins have a cheap job at £15LNB from maplins the cheapest is £15 at most. ( the cheap one would be fine using a 13v/18v supply)dish size, i myself think small is better, to start with a small 60cm setup.if we get some decent data from them, upgrading is a simple affair,just replacing the smaller 60cm for a larger. the same LNB could be used.the main problemi see is the LNB, best to have all the same make/model. otherwise could have problems from slight differences in the LNB'sit would be like having, 20x SPC900NC collecting frames and 10 xbox/asda cams doing the same. then trying to stack and align the two,so lnb is best to be the same all around, cheap, easy to source, and single output only (quad connection lnb cost more than a single output and requires capping off)best place to start, kelling heath star party or somewhere alike. just 5 dishes would give us some useful infomation. using a large object (the sun/moon/ polaris) as a test subject. and pen to paper readouts over a time period.As for hardware:1x dish1x LNB2x coax cable ( max 10ft say)power source ( car battery charger / lithium ion cell pack from cordless drill (14.4v)1x signal meter ( best using the cheap type none digital, keeping cost down and simple to use. )could an arduino/blackfin measure the signal strength ? if so it could be saved via memory stick shield. Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Sorry James, what's NTP?Yes, Sorry James, what's NTP? I don't think mixed dish sizes should be a problem - some current professional VLBI arrays use various dish sizes, in fact I think it's actually a benefit rather than a problem. The SKA will use 2 different sizes of dish, the large ones in SA and the smaller in Australia.4 ns sounds just about accurate enough. I've been looking at some of the potential targets and some deep sky objects can be recieved at around 1400 MHz, which would be a period (T) of over 700 ns. Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 D'oh! Sorry - didn't notice this second page!Yeah I think NTP might be a bit difficult - especially if GPS does turn out to be accurate enough. One question I'm not sure about - would we only need one central GPS clock, or would we have to have one at each telescope? Link to comment Share on other sites More sharing options...
Enrico Posted June 10, 2012 Share Posted June 10, 2012 Would DCF77 (the Frankfurt time signal) be good enough?. It's driven by Atomic clocks and it's position is known, so each dish can correct for distance from it if necessary to be that accurate.I'm guessing, but is it only important that the dishes "synchronize watches" when they all start capturing data (and maybe at the end)? In which case, it does not matter how accurate the pulse is, just that they all use the same pulse to start recording.... Link to comment Share on other sites More sharing options...
Enrico Posted June 10, 2012 Share Posted June 10, 2012 Oh, and I'd love to be part of the project somehow. Not sure what i can contribute apart from a location....(my degree is in physics, but it was more years ago now than I care to admit...).N.b. loads of used and new satellite dishes on fleabay if those would be any good.Agree with a previous post that would be good to standardize some of the downstream hardware to minimize any potential errors. Link to comment Share on other sites More sharing options...
Enrico Posted June 10, 2012 Share Posted June 10, 2012 N.n.b. DCF77 receivers available of eBay for just over a tenner.... Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 I'm guessing, but is it only important that the dishes "synchronize watches" when they all start capturing data (and maybe at the end)? In which case, it does not matter how accurate the pulse is, just that they all use the same pulse to start recording....Pretty much! Not sure how much info you get from the DCF77 - for 'civilian' purposes, you only receive up to the millisecond (at best) interval. We would need more like nanosecond of tens of nanoseconds, I think. But I will investigate nonethesess, becaus said clock definitely has that precision, just not sure if it broadcasts it all.... Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 DCF77 with normal grade equipment only recceives an accuracy of +/- 0.1 s. Even with research grade equipment, still only transmits at around 20 microsec. So won't be hot enough. Shame really, that would have been a ****easy solution! Link to comment Share on other sites More sharing options...
astromerlin Posted June 10, 2012 Share Posted June 10, 2012 Excuse the butt in, I know nothing of the subject but I'm interested al the same. Is it not possible to recieve data and use a known pulsar to syncronise the timing? Link to comment Share on other sites More sharing options...
Enrico Posted June 10, 2012 Share Posted June 10, 2012 ...according to some quick reading on the DCF77 topic, you can get 50 microsecond accuracy if you decode the FM signal hidden in the pulse (the "normal" signal which consumer clocks etc. receive is an AM signal). Still not near enough.Ideally, the time signal would be one that is received by the actual detectors being used for the radio telescope, i.e. a trigger or signature in the data (from a known point source at a known location) Link to comment Share on other sites More sharing options...
jamespels Posted June 10, 2012 Share Posted June 10, 2012 OK, thinking about this a bit more...Timing: what we are trying to achieve is a way of synchronising the tracks from each receiver. This means we need to have accurate "ticks" of a known interval (e.g. one second, or anything else convenient) and that we need to know roughly when each tick is but this does not need to be massively accurate (+/- a few tens of milliseconds?). We need the ticks so we can put the signal peaks and troughs in the right place for interferometry; we need to position the tracks in time so we can synchronise them without the software having to spend forever and a day finding the right starting point. NTP wont work because with variable latency, we won't be able to guarantee each "tick" is one second or whatever apart. By the sounds of it, the Frankfurt time signal will not be sufficiently accurate. This really only leaves (of the suggestions so far) GPS - we won't necessarily know the exact time of each "tick" but we will know they are consistent, whichever satellite the some from; furthermore, we will know approximately what time each tick represents because that is the whole point of the signal. We may not know how things vary from one satellite to another (I imagine we would pick up many over the course of a day) but we can at least see when they change and start a new track when this happens.To answer a previous question: yes, we will need one clock per site - the important bit s going to be encoding the time signal in each track so we can synchronise later.Coming round to low-cost alignment, I think a modification on drift-scanning is going to be the best bet - we all align on the same spot and allow the scan to drift with the earth's rotation. At the end of each period, we drop the target point 1 second south and repeat. This will mean we need to accurately align during setup but a relatively simple, low-cost mechanical contraption will allow us to control the alt, while keeping the az the same throughout. This setup will be far, far cheaper than a goto mount and can be made to any strength we need, within reason (it could even be manual to start with).Regarding the signal strength, anybody have any idea what selectivity & sensitivity we will need? Will a commercial grade LNB designed to pick up relatively powerful satellite TV signals cope with this?Still thinking... J.p.s. Somebody mentioned trying this out at a star party. For those who were on a different planet last year, or who have joined since last October, I am running PSP2012 and am happy to host & demo anything there. Just to note, though, we are not going to get any meaningful interferometry from locations on or around the site itself but it could be a very good tech demonstrator. Link to comment Share on other sites More sharing options...
badgerchap Posted June 10, 2012 Author Share Posted June 10, 2012 Excuse the butt in, I know nothing of the subject but I'm interested al the same. Is it not possible to recieve data and use a known pulsar to syncronise the timing?In principle, it's a cracking idea - problem is we'd 1) need a second dish at each site which would have to track our pulsar constantly and extremely accurately and 2) we'd have to find the beggar first!Coming round to low-cost alignment, I think a modification on drift-scanning is going to be the best bet - we all align on the same spot and allow the scan to drift with the earth's rotation. At the end of each period, we drop the target point 1 second south and repeat. This will mean we need to accurately align during setup but a relatively simple, low-cost mechanical contraption will allow us to control the alt, while keeping the az the same throughout. This setup will be far, far cheaper than a goto mount and can be made to any strength we need, within reason (it could even be manual to start with).Regarding the signal strength, anybody have any idea what selectivity & sensitivity we will need? Will a commercial grade LNB designed to pick up relatively powerful satellite TV signalsRegarding signal strength, not a clue. I will attempt to work it out over the coming few days if I get time, but the house is about to be invaded, so might take a while!As for the drift scanning, I think that's just about the most sensible idea we've had so far. Much more simple, plenty effective and shouldn't cost nearly as much. One sticky bit though is we'll have to be darned sure that each time we move up or down a notch, we all do it by precisely the same amount. I think either a preprogrammed movement or some kind of synchronicity between dishes would be the way to get around this, and seeing as they'd all have to be linked up anyway, the latter is probably best. I'm not sure how we'd exact this control though. I think we'd all have to build a similar altitude bearing and actuator, and have it controlled simultaneously and remotely.Tell you what boys and girls, this ain't harf gonna be complicated. Fun though! Might take a few years to get it right.... Link to comment Share on other sites More sharing options...
jamespels Posted June 11, 2012 Share Posted June 11, 2012 Regarding signal strength, not a clue. I will attempt to work it out over the coming few days if I get time, but the house is about to be invaded, so might take a while!This this may be a challenge using off-the-shelf kit. From http://members.shaw.ca/skywave/radio.htm:With successful solar observations under my belt, I decided to try looking at the Moon and other astronomical sources to see what I could detect. The Moon emits microwaves originating from its temperature. The nearly Full Moon, as observed April 10, 1998, produced a signal response of 3 mV, one tenth the strength of the solar response.The dramatic reduction in signal strength between the Sun and Moon made me wonder if I would be able to see more distant objects. Attempts to see sources known to be strong radio emitters, such as Cygnus A and Taurus A, were not successful. Reference charts showing the strength of signals from such sources compared to the signal strength of the Sun at 12 GHz, clearly showed that I was dealing with emissions so weak that I would probably not be able to distinguish them from the background noise created within the receiver system itself.The author make the very valid point a little later on that technology is changing very fast; this article was written in the late '90s so we have had a decade and a half of progress since then. Either way, I think the reference somebody earlier made to peltier coolers may come in before too long! Link to comment Share on other sites More sharing options...
Stargazing_Cliff Posted June 11, 2012 Share Posted June 11, 2012 My older brother is into Electronics and coding stuff Think i'll ask him about radio astronomy and i shall start looking for some old satelite dish and i think i know where one is Very interesting to know you can make small mini radio telescope.I know you can buy satelite starter kits for around 50 pounds Just woundered if they would work ? or does it have to be the older satelite dishes ? Link to comment Share on other sites More sharing options...
jamespels Posted June 11, 2012 Share Posted June 11, 2012 Tell you what boys and girls, this ain't harf gonna be complicated. Fun though! Might take a few years to get it right....OK, my take on this is that before we can go out looking for additional sites and trying to work out interferometry, we are going to need to spend a lot of time just getting the dish and electronics right. I suggest we concentrate on this first as we are going to need to be a bit inventive to get a suitably sensitive system with accurate timing and alignment for a realistic price.Incidentallty, another helpful article on the basics here... http://www.nationalstemcentre.org.uk/elibrary/file/3022/SATIS_1207_1208.pdf. From this, beam width in degrees is approx 60 x wavelength (lambda) / dish diameter. If we want to observe at about 0.2m lambda and want to achieve one arc minute (1/60 degrees) resolution, this suggests a minimum dish diameter of 0.2m so the 1m dishes suggested previously should be OK (barring nay other factors I don't know about yet!!!).Finally, very important point... we need a name and I suggest "LARA" (Large Amateur Radio Array, not the explorer )J. Link to comment Share on other sites More sharing options...
garethmob Posted June 11, 2012 Share Posted June 11, 2012 soooo how do we link the skydish to the computer? Link to comment Share on other sites More sharing options...
jamespels Posted June 11, 2012 Share Posted June 11, 2012 soooo how do we link the skydish to the computer?This is where Badger comes in... The LNB will connect to a box of electronics that plays the role of the bits & bobs in your sky / freesat box; this will result in a single output in the form of a DC voltage, the amplitude of which represents the intensity of the signal received. To my mind, this is where the first real challenge comes in: the box of electronics doesn't need to be that complicated as it isn't doing anything that clever, BUT the signal we will receive is very small and will be lost in the background noise in most cases. To avoid repetition, please see my comments here about this (I am trying to keep radio-scope design to the other thread; array design to this thread - not sure how successful that will be, though!).J. Link to comment Share on other sites More sharing options...
badgerchap Posted June 11, 2012 Author Share Posted June 11, 2012 I think you're right there, best place to start is with the dish(es). My suggestion to build on this would be that we should first start by just having a play around really. The difficult thing about being all over the country is that we're all going to have to do a lot of working things out for ourselves, but this also has the benefit that we should each get a better understanding of the tech. For me, I think I'll get a 60cm dish to test the concept, as this was the first amateur radio telescope I ever saw! If I can make this work to pick up the sun and moon, then I think it's worth moving up to a 1m dish - I would point out that the 1m dish shouldn't be neccessary for everyone - there is no reason why people can't stay with a smaller dish, or why they shouldn't fork out £3000 for a 3m dish, if that is their wish!Good suggestion for the name - I'm gonna throw another one in there for the sake of variety: ARIA (Amateur Radio Interferometry Array) Link to comment Share on other sites More sharing options...
badgerchap Posted June 11, 2012 Author Share Posted June 11, 2012 soooo how do we link the skydish to the computer?Hoping to nick some software for this, watch this space - in 'discussions' about this at the moment Link to comment Share on other sites More sharing options...
badgerchap Posted June 11, 2012 Author Share Posted June 11, 2012 Right peeps - I've got me an expert - Radio Astronomer from uni on board - at least to answer some questions anyway. Could people please supply some ideas for questions I can ask him - basically I want to check the feasibility of this before we all start rushing out to buy stuff, so questions in that frame of reference would be good. Thanks guys - and can I just say how stoked I am about how many people seem to be up for this? I'm amazed to see how many responses this has got!ThanksBadgerchap Link to comment Share on other sites More sharing options...
Mr TamiyaCowboy Posted June 11, 2012 Share Posted June 11, 2012 importance of time :this is where we are hanging trying to solve the time problem. signal, we are new at this so we need a fairly simple signal to chase. what is an ideal target signal for a small set up like what we will own/useARIA gets my vote sounds sorta cool and technical Link to comment Share on other sites More sharing options...
badgerchap Posted June 11, 2012 Author Share Posted June 11, 2012 I reckon best place to start is the sun - it's pretty hard to miss! Link to comment Share on other sites More sharing options...
JamesF Posted June 11, 2012 Share Posted June 11, 2012 I reckon best place to start is the sun - it's pretty hard to miss!You never mentioned that you'd emigrated.James Link to comment Share on other sites More sharing options...
Mr TamiyaCowboy Posted June 11, 2012 Share Posted June 11, 2012 You never mentioned that you'd emigrated.Jameslol jamesbadger is looking ahead to a time where we can see through clouds only reason he wants a radio telescopei think it is the reason we are all interested in the project to. Link to comment Share on other sites More sharing options...
badgerchap Posted June 11, 2012 Author Share Posted June 11, 2012 lol jamesbadger is looking ahead to a time where we can see through clouds only reason he wants a radio telescopei think it is the reason we are all interested in the project to.Nail - head - job done. Link to comment Share on other sites More sharing options...
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