How to make a Radio Telescope at home

see yes yes i just switched on the video okay fine so good afternoon uh i'm ram so today i i think in the last couple of weeks back we had discussed about having a session on on this home built radio astronomy and radio telescopes and that was the subject that we are planning to do today and what i am planning to share is our experience of building and uh and and doing some astronomy out of the radio telescopes that we have built at home uh when i say we i also have sri rang who is also joined nepal so srirang is currently not work but we both have built this radio telescopes together so today i'm planning to present two radio telescopes which i will probably show that later as well but uh along with me sri lanka and we both have built this together and uh just to share a small journey around uh a year year and a half back uh we both were together uh studying uh a postgraduate course in astronomy and astrophysics so as part of the course one of the subjects was radio astronomy so as part of the radio astronomy course which was one of the subjects we did visit the governor radio uh telescope facility so when we visited as part of our educational tour and all that so that's when we saw uh what was being done there and then over just a casual lunch discussion in the uh in government itself in the facility uh myself and sriram we thought why can't we build one uh where we can we can do some some radio astronomy out of it so that's how the journey started around that was uh sometime july august last year and then and in the first trials that we did was after three months we were able to assemble and build something within two two and a half months and then we started our first trial and then as part of this course uh we did present a paper which is a part of our dissertation uh to complete this course and uh and the paper that we presented was on radio astronomy and how we can build radio telescopes at home and do some uh observations and grab some science out of it so that's the uh that's the just a prologue of what we did and i'm sure here if you have seen the camera what you're seeing here behind me is one of the uh radio telescope that we have built this is a new antenna which we have designed uh during the lockdown we have designed couple of them this is one of the versions and this version that we have designed uh is the is for the hydrogen line observation which i'll also try to talk about that in the next few slides so that is the prologue and what i'll do now is switch off the camera and start the presentation i have a set of slides uh which i feel is much easier to walk through and talk about it and that's how i plan to conduct this small session i hope it's okay so just switch off and so one more small solution i think this talk is going to be of uh some utility for some of my students also who do projects if you comment then can i just pass on this sure question to them sure so sure okay [Music] let me know when you're able to see the screen okay yeah so here is uh here is the couple of pictures of the actual radio telescopes that we have sorry sir but your screen is not visible to us okay right right okay thank you it's visible okay now now it's okay now okay so i'll just walk through a set of slides now that's where uh now the pictures that has been uh put here is uh is the actual pictures of what we have built and on the left side where there is a dish antenna uh that's a that's a solar radio telescope which is used for chromospheric observation and then on the right largely uh enlarged i'm not sure if others are experiencing that i'm not able to see the full slide but one portion of the slide fully maximized not sure why oh is it uh is everybody experiencing the same or should i and there's something text on one side i think it is okay to me i don't know okay for me okay [Music] yeah that's uh that's the full uh picture uh what i just did let's check the whatsapp that's the full picture that's true and there's i think maybe srisha needs to just recheck on his video [Music] [Applause] okay okay uh can we continue okay are you sure sure okay so yeah on the on the left side the parabolic dish uh is is the solar radio telescope it is based out of uh ibt design ibt stands for atp telescope uh i'll talk about that once again later and then on the right side um is is about the 21 centimeter hydrogen line detection it's a radio telescope for that and you see um three telescopes there each one of them are actually uh different versions of that it means that it goes uh from down to up its many versions that we have been building for the last one year plus more and each one of them have got its own distinct advantages in terms of gain efficiency and resolution and bandwidth and so on so which we will also try to take a short look about it later as well okay so i plan to start with giving a short introduction of what radio astronomy is all about uh now and what's the difference between visual or optical that is normally done versus what is radio now uh the basic difference between radio and visual are both are electromagnetic waves once again uh it is just that in in case of uh radio you can look at this particular picture on the left side uh it where what radio astronomy does is that it studies the emission of radio signals from celestial objects at radio frequencies and where you have a visual spectrum which is around 400 to 700 nanometer radio telescopes observe the skies in wavelengths from centimeter to a few meter so that's the difference between the electromagnetic wave length differences uh between radio and visual so visual is in in a very small wavelength is the visit this is the visible part i just brought so uh is where here so this is this is where radio astronomy comes in now from the point of view of the window of observation uh i'm just shifting to the slide on the right you can take a look over here that this is the visible light that we can see and this is a very narrow band whereas when you look at the radio radio is a very wide band application that means you can see uh you can resolve a lot many more objects in radio frequencies when you use radio telescopes than going visual there are certain distinct advantages as well when you compare both most of the time optical signals are or do have a lot of bearing on how the atmosphere is the turbulence of the atmosphere the weather the cloud and all that but a radio uh does not get into uh those kinds of interferences it is able to uh much more resolve a much more wideband plus also not getting into all those atmospheric seeing uh kind of challenges which optical um signals do have so that's the main difference but there are certain places in which even radio uh is not able to resolve uh those are typically infrared uh gamma rays and uh long wavelength radio waves which are typically blocked by our own atmosphere uh now that's uh that's the major difference um and when it comes to radio versus the visual uh the only advantage once again i try to repeat is that we get a much broader uh observable window from the earth than compared to an optical window okay so uh there's no hard and fast rule if you have questions please stop me then and there and we can keep discussing about it so the next uh i'm trying to go much more a bit more deeper into what radio astronomy and how we how it really helps us now once again this slide is about the comparison between the optical and the radio windows now when we can see it is a very broadband radio window here and what this picture talks about is how atmosphere most of the time does have a bearing on what we observe in the optical window and how the atmosphere does not have too much of bearing when we observe something in the radio so when we start talking about the atmosphere various layers of the atmosphere right from troposphere stratosphere uh thermosphere and mesospheres and each one of them have a certain level of absorption and kind of when light does come through the atmosphere it does affect the atmosphere does affect the way that we see the or visualize certain objects that's why uh many of these telescopes like hubble are placed up in the sky uh where it is free from all the atmospheric turbulence of the earth and it does have a very clear view of the celestial plane so that's where many of the telescopes like hubble and all are placed and since infrared is blocked by the atmosphere there are specific satellites which are placed which do capture celestial objects in the infrared spectrum and then there is x-ray chandra x-ray telescopes and then there are gamma values which can also be detected using certain satellites now for the radio window especially since it's got a very broad spectrum many of the observations or most of the observations are earth centric so they do mostly from the earth itself and that's that's what something which is interesting um so this is just at the end of the slide i have just kept a small idea of how we can compare the lambda and that is the wavelength of a particular radio frequency and convert that into frequency and what's the formula for that so lambda is the wavelength c divided by f gives us the wavelength c is the speed of light and f is the frequency you can always do conversion so most of the time if somebody tells you that we have to observe a window of 21 centimeter then you'll have to find out what is the frequency that will have to um build a antenna or design an antenna for and then you can use all these formulas to do all that conversions and and find out those basics so just left it like that for that uh now i'm just going into a detail about uh what we can do as some projects uh as most of us are mature astronomers here what we can do as some radio astronomy projects using sdr uh we'll talk about sdr also sdr is called as a software defined radio so it's it's just a small electronic gadget uh where it has got all those uh amplifiers low noise amplifiers sometimes filters and then it comes to the complete package of even coding decoding encoding and all that in in one single small device um so that's sdr so you can do various projects of radio astronomy using that device i'll also show that device later and these are a few examples of what can be done as a radio astronomy projects which you can do yourself at home uh and so on so i'm just trying to give a brief introduction of what all can be done um so ionospheric monitoring can be done um and uh this is at ultra low frequency and very low frequency and um mostly at around 30 to around three three to thirty and megahertz and kilohertz and hertz um and jupiter jovian is typically the jupiter so jupiter also emits radio signals because of its very high dense magnetic fields concentrated near its poles and jupiter has got its own rotational pattern where we know that it does the cross station um and of of its gaseous medium and because of that it does produce a lot of radio signals and those can be detected using antennas from here on earth and that is detected using uh at around 150 to 250 kilohertz so this this is something which is also done by hobby enthusiasts and then you can do a lot of solar observation uh typically solar continuum solar wind observations at very high frequency and then many of the observatories even in india like gauri with north they observe solar at around 70 to 135 kilohertz uh that's their observational window and they have built a large aperture telescope there if somebody has seen it even on the web you can see it's a two kilometer long uh telescope which has got a lot of yagi antenna array and uh they observe uh sun and map the sun using a radio medium and then you do have a pulser observations that you can do and typically it is from 70 to 406 kilohertz and you can design your own antenna and do a pulser observation so and typically uh one one basic thing is that so long uh the wavelengths become the frequencies are lower and lower uh the wavelengths are broader and broader the antennas have to be much larger in size and uh and once the wavelengths become shorter and shorter that is in frequencies become higher um the antenna can be smaller so the portability does come when you have a certain something which is a very high frequency so that's why most of our cellular phones does have that portability because they operate at around microwave wavelengths um yeah that's uh that's some basic and then yeah we do we can also do a lot of solar observations uh i will come to that part as well sun is a is a great radio source it emits a radio um multiple bands of radio frequency bands and that's that's something where you can observe sun in its many dimensions using radio frequency we'll come to that later that's one part that we can discuss and of course uh this is the 21 centimeter hydrogen line uh that is something that can be observed uh plus the sun also emits something at uh a one four two zero that is one point four two gigahertz which is solar continuum continuum is typically a continuous signal which can uh which will come from sun and that this can be observed and captured as well uh through radio frequencies spectral is typically the uh hydroxyl radical this is used in uh mostly astrobiological applications now also in seti uh city is stands for uh society for extraterrestrial uh research and and they also find out if there are any other uh living sources other than us somewhere in the universe lurking around and they they use these methods to find that out oh h typically because there is an oxygen and hydrogen kind of a combination always if you find something here the idea is or the the hope is that you can find somewhere a life other than us in somewhere in the universe so that is also used uh in in radio frequency observations at 1.6 gigahertz and 1.7 gigahertz so these are a few projects that can be done i have stopped it around 1.7 but there are many as others as well but many of the commercially available sdrs operate better at only up to 2 gigahertz and after that you will have to have some special sdrs which are typically radio astronomy sdrs which are not that easy to procure in the market but there are many other projects that can be done here a question am yes so these radio telescopes they are limited for visual observation or they're used for imaging no imaging comes out of this shri no imaging comes out of this uh this is purely uh where i can show i'll show you actually i have a few videos what you really get as signals so you will be able to see signals that means waveforms which which form or pulses that come out uh typically once you are able to resolve a target and from there you capture all that data and then you can do a lot of analysis from where the source is what is the what is the um what is the source made of and so on and so on so i'll show you but there's nothing optical is nothing that you can do with word radio okay okay so for a research purpose and understanding specifics of the target yes okay and also what radio does what visual cannot do is that it can go much far or farther than than optical right yeah got that yeah yeah so that's a distinct advantage and and the you can do a lot more science with this uh than optical optical uh does give you all that visual depth and clarity and pretty pictures and so on but here a lot more science can be done we'll talk about that some in the next couple of slides of how it is really useful okay yeah so uh now coming to what we have done um um what uh and myself here we have done is we have built two or two radio telescopes uh one is for observing the sun's chromosphere uh and that's at around the emission is at around 10 to 12 gigahertz uh from the sun and we are observing that here through our own ivt based design and then hydrogen line telescope a hydrogen line is emitted from a la a lot of galactic sources supernova remnants and so on we will also get to know why it is so important in the next few slides and that that is what we have built these two telescopes is what we have built in the new design that we have done um we do have uh it it's it's uh it's an optimistic or a design where we are planning to also use this in both spectral 21 centimeter hydrogen line also uh to try to do something with the oh uh hydroxyl radical uh kind of observation um but this is still yet to be tested we have just designed this and the hardware is all ready um right now we are doing the design of experiment to actually put this together and start resolving uh and getting information so i will go a bit more detail into um what we have done uh the first introduction is about uh the the the chromosphere radio telescope which we operate for observation of the sun's emission from the chromosphere and uh and this slide talks about what does sun radiate and and what what is this is sun radio source so and how it is a radio source and why it is so important to observe the sun in radio frequency so sun is a great radio source and what it does is that it emits in a in a very broad band uh in terms of radio right from 20 megahertz to 20 gigahertz it can be observed which is a very very large band um apart from whatever we visually see using h alpha or or any of those visual observations of of this sometimes we also see all those coronal mass ejections and photo sharing dispersions and so on but and prominence is of course using all that visual telescopes but radio is also very very important observation that people have been using uh for observing sun because of uh because of the broad amount of frequency that is emitted from the sun so if you look at the picture there um so each layer of the sun emits a radio uh frequency uh the photosphere does emit plus there is also emission coming out of chromosphere then there is a continuum solar continuum coming which is typically the radio sun which is every day sun as it starts shining because of its thermonuclear reactions and there is a continuum which does come and this is also observed here and mapped and if you look at this graph on the right side uh i'm trying to point it towards a small rectangle within the graph so this gives an idea about the frequency say from 10 megahertz to almost 30 gigahertz so you have various kinds of emissions which are coming so wherever there is this cross lines uh they are all called as a solar continuum which means it's a continuous emission coming from the sun and each one of those continuum is coming in from different layers of the sun so the there is decimetric continuum then there is asymmetric continuum and so on and then there is this microwave continuum uh this is where we have done something about and this is coming in from the chromospheric part and there there's also this decimetric continuum uh which is also coming in from the sun and uh this is also resolved through uh the uh the new radio telescope that we have built and i think about a couple of weeks back i just put the graph about what we have resolved so that resolution was sun's emission coming from uh this part of the decimated continuum and uh so that's how you can observe through radio and how do you start capturing and what you can do is in the next few slides i can explain but what this this graph shows is that as and when there is a lot of variation which is happening on the sun wherever there are sunspots which are either at the maximum or minimum when there is a quiet sun or if it's a normal sun or there is a noise or there is a burst all this can be found out through radio and that's how it's very very important that people do observe the sun um and uh because there might be so much of coronal mass ejections sometimes which it does happen and many of the satellites which are orbiting um the earth and they're all made up of electronics a ton of electronics do work on earth and if there are coronal mass ejections which are of very wide a high intensity there might always be a burnout that means that all these electronics chips are electronics they just stopped working and they're having uh these kind of instances which are happening earlier and uh they do observe a sun for those reasons uh not visual yes but radio is more to observe those kinds of rejections okay i'm i'm just going uh into the next slide where it this slide talks about more of our own design and what we have done so what we have done in our case is uh we have just taken our dish antenna this is a normal parabolic dish antenna which was uh which is used for all our cable tv receptions so i had a spare one which was uh used for earlier dish tv or something so we just we just modified that uh for observation of the sun now the reason that we used uh this this kind of cable tv this antennas is that uh we have we would have seen an lnb uh in front of the dish antenna a small block which is typically there uh it's uh it's a waveguide called as low noise block what that does is that whenever the dish antenna is pointed towards the source uh in this case when we are trying to look at all these satellite tv channels uh if you point it towards uh the satellite um where if it's earth and trick that means that it's always the same so somewhat at the same point so it starts beaming uh there and they use l-band uh l-band is typically what they use and uh uh and here the l-band uh these kinds of uh elements work from around 10 to 12 gigahertz that's where our satellite eu reception comes in so you can use those lnbs which which is normally used for satellite tv reception and do some modification to start uh getting signals uh from the sun for this so that's exactly like perfect excuse me can you please hide the notification at the bottom regarding presentation oh sorry yes please okay okay is this okay yes okay so we use an lnb can you explain about uh what are the modifications you have done with lnb yeah i'll come to that [Music] now the lmd assets does not require any modification and they'll then be whatever you are having in a satellite tv reception you can continue to use that so the only change that we have done is that normally what you have at home is a is a single port lmb unless you have uh two connections where it's using a a single satellite dish but you have two connections at home otherwise most of the times you get a single port lnb instead of that we ordered a dual port lnb so it's not that um that's expensive uh you do get it in amazon and all these places it's around 500 to 600 rupees so if you use that you get a dual port lmb and then what needs to be done is that you take that and you have something called as a satellite tv signal receiver it's a small uh red color box i'll show you that i do have a picture so what it does is that many of the people who come and install these dish antennas at home they use this to measure and find out where the signal is coming from which direction and then they you know bolt it and go so it's a small device uh which works on on an 18 volt battery and so on so what it does is that as soon as you turn the dish antenna in the direction of that satellite uh it just gives you a um there is a there's a meter there so it it just the needle starts uh you know pointing towards uh towards the higher band and it gives out a buzz or a beep so that is what is used and then even this is available uh this is very very inexpensive it's around and you use a normal coaxial cable which comes whatever is used for your dish antenna the same coaxial cable can be used and one of the ends of the coaxial cable now needs to go to uh these satellite freeway reception meters and then from the other port this is connected to uh from a coaxial cable rg6 to rg 174 there is a conversion that i have done so that means you just start the coaxial cable which comes with the cable tv and then you have to give it to a slimmer one i will show that later and then this can go into your rtl sdr receiver and then this will plug in via a usb socket to your laptop and then you can use some software called as sdr sharp or a radio sdr and so on and and then you can start uh receiving the signals from the sun when you start pointing the antenna to the place where because the sun is there in the sky that's that's how simple it is uh in in terms of uh actually building the whole stuff i have a question yeah so uh uh the input from in the rtl whiteboard lna it okay so now i'll just talk about that now the 18 words which has been put there is uh if you if you uh if you look at what we have at home all our cable tv receivers uh there is that uh there is a box right uh which is which actually one of the end of the box connects to the tv and it has got a coder decoder box isn't it the scene goes right small ones which plugged in near the tv and then you use a remote to switch the channels and you it comes with the setup box correct now the setup box what it does is that the one end of the setup box is connected to the coaxial cable right so the setup box it provides around 18 volts as a back voltage for the lnb to operate this lnb yeah to operate what we are trying to do over here is artificially providing this you you can you can use an 18 volt power supply uh a dc power supply and then a small uh inductor isolate it and directly feed it through this satellite meter and this lnv gets powered through that and then this is able to receive all the signals i'll show you i have a video yeah actually so that's uh that's the mode of operation and then you can use a set of software uh to start reading the signals this is how it reads uh when you open the software and this is at around 1.2 gigahertz so what this does is that this lnd it takes the signal coming in incoming signal at around 10 to 12 gigahertz and down converts it to 1 to 1.2 gigahertz so and then this uh down converted signal is what is going into all these white band lna whiteboard lns stands for a low noise amplifier it's just an amplifier to amplify the signal which is coming in from the lnb and then we are feeding it to the rtl sdr receiver uh it just it just gives a bump in the signal and gives some amount of stability and you can do a lot more analysis when you open up all these uh free fourier transform softwares like like this hdr and then radio sdr and various softwares which typically do all that and this is a this is where we are trying to go on at one point two gigahertz this observation you are able to see a spike here a peak we're able to see this peak here right so this is the signal coming in from the sun if i switch off this uh this 18 volt uh this this whole signal will die down and it will be a it will be a flat noise here as soon as i switch on um and if this this whole antenna is pointed towards the sun i will get this spike so this is how the signal from from a celestial source is received and then you can have all these meters and plug-ins and so on which will show you what is the strength of the signal and then you can store all these data and do a lot of analysis come to that yeah this talks about what are the dimensions of uh of the dish that we have used and we just use the counterweight to balance uh 2 kg counterweight this is the actual picture um the the red and yellow part is the lnb uh which is it there are two ports here and then one of the port this is the satellite radio uh it is just a signal um receiver it's a small box this is that box and then one port is connected uh to this where it detects the signal and the other port uh via the rj uh the coaxial cable and then it is connected to the laptop so this is uh this is the biggest setup of the radio telescope just put this on on a normal tripod which which is used for most of our camera a bit sturdy one because uh this whole thing weighs around three and a half kg and put two kilos of a counterweight this is a normal counterweight which is used for as an ankle weight in most of the exercise that you do in gyms so that's what i used okay this particular thing is not a tracking device i'll show you the other one which we have built for 21 centimeter that i have mounted it on the ioptron sky guider pro it's a it's a very lightweight equipment that we have built as an antenna that keeps tracking that is used as a tracking device that can use the track this is not okay so i'll just show a video no uh now uh there's a on the left hand side if you see um there's a picture here uh of of the dish antenna and there is a set of mirrors that have placed on this antenna right and then the sun as reflection falls in the mirror and then it's uh getting illuminated on the lnb part here the yellow color part you can see this so this is very important to find out because many of the parabolic dishes that you get uh either are center focused or offset focused so what we had tried to do was that this particular dish was an offset focus now we wanted to find out what is the degree of offset it is uh so that when we point it towards the sun uh it means that it's just like you know you see the sun and if this telescope is in alignment it will not work because it's enough stack so there will be our 10 or 15 degrees difference so that's that is what we wanted to assess uh before we actually do the experiment and uh in order to do that assessment we just use some mirrors and a small set of piece of mirrors which you get in any of those mirror shops and put some magnets around it with a sticky tip and place it on the dish to find out the offset and then we'll have to also do some final focus adjustments here just to ensure that the right amount of sun's energy falls on this and and it's in all good focus that we can get a high density output so these are a few things that you'll have to do once you build them okay now what i do is that um let us switch on the video um just a small suggestion can we also paste small specs of aluminium foil on the dish itself rather than mirrors here you can use your own method you can use your own methods that is fine okay thanks yeah you can use radio you can use aluminium as well here because we are able to visually see the sun much better and most of the time it so happens that if you have high reflectivity like a mirror uh you can visually also see the kind of beam which is forming on the lnd yes that sounds as a decent indicator yeah when you're in the right sun to make out the difference it is useful right right okay i'm just switching on the video do let me know if you are able to hear the audio as well are you able to hear the audio no oh one second uh i will try to do it let me know if you are able to see and this is the satellite db meter you can see the needle has pointed more towards the right that means it is receiving the signal and then these are the lna and the sdr and this is how the output looks on the screen and what i was trying to point over here is what's the relative temperature that when we are taking this observation so that is why it was just pointing towards the thermometer and i'll try to show the next video so let me know if you're able to see or hear this noise as well what this does is that you can look at the needle here it's moved towards the right that means it is towards the sun it is moved towards the right now as soon as i physically try to you know move the telescope or towards right and the left where it is going away from the sun the needle kills towards the zero and then it starts coming as i move towards the sun it becomes it comes towards the right so it means that's how the signal is getting received you can see that right when you physically move the telescope which is either towards or away from the sun there is also a difference in the signal yeah so this is how a basic operation of the radio telescope um any questions on this obama they used these uh similar radio telescope setups for uh capturing recently this is a black hole right blackwell imaging and they presented that last year um but you said these radio telescopes cannot do any capture of image are those telescopes different from this one what are you sure also this is what i read yes i'll try to explain that so what they are doing there is adding false color okay so it means that what you are trying to get over here you assume that you are getting one pixel okay so this is one pixel one information you're getting one pixel assume you are putting an array where you can get a pixel of say one zero two four by seven sixty eight that means that you need to have a lot many such telescopes working in coordination and every every each one each and each one of them will receive a signal and then they uh integrate that signal in a typical bit of 8-bit or 16-bit and then convert it into a 3-dimensional pattern or a 2-dimensional pattern okay okay okay so basically it is not a direct capture of image but the signals are interpreted by some software and they then convert it into an image exactly those numbers get represented in colors especially you know for cities like bangalore where it is cloudy whether a radio telescope imaging system can be done uh where you know we can actually image even if there are clouds and you know the signals can be converted into pixel images and then you can actually start imaging it i i keep thinking about that that is practical feasibility yes it is practical it is just that what needs to be assessed is what is the celestial object that you are trying to resolve number one and to recall much smaller and smaller distances you will require higher and higher power so you need to also calculate the aperture in terms of power to resolve and also the power in terms of power itself uh what what is the kind of electricity required and the amplification which is required to do all that i think so what srisha is willing to do is that can be achieved through raster scan of a patch in the sky okay so that will give a plot of the strength of signal that we can make out something for the visual i think that that is possible and that is what's done by the professional uh radio telescopes yeah i'm just trying to show and i've just gone to the next slide which partly answers that question as well now if you look at this slide on on the top left there is a frequency spectrogram right now what the spectrogram does is that uh using the same setup that you have done which was done there we we run spectrograms spectrograms are nothing but you take a bandwidth say we were resolving a signal at 1.2 gigahertz so what i want to do is that i want to find out at 1.15 to 1.25 which also includes 1.2 gigahertz what is the strength of signals that i am receiving in each one of these bandwidths i run the spectrogram where it will run a series of scans so it might run around 12 15 20 100 whatever the length that you want to or the frequency and what you want to and this spectrogram tells you that when i run it around 15 times 20 times where is the maximum i am getting you are seeing all those blue things here right and then there is a peak which is marked by a red cross there and it shows 1.2 so this is in megahertz when you convert that into gigahertz it is 1.2 gigahertz and every time when i when the peak i am getting is that around 1.2 gigahertz so what what this is is that the signal strength that i am getting at maximum when i have point pointed to a particular region in the sky and uh and resolving as a particular celestial object on a day time latitude longitude all that you can um you can record this for this is where i am getting the maximum signal strength and that is where i one is what you visually saw in the software which was down below and the screens which are here in the black backgrounds where you see those spikes but these are spectrograms where you you run those scans by energizing the antennas and then you get a response out of it and then you can start doing a lot of analysis through this as well this is not nothing but what the professor's favorite was telling that you can run a scan so this is exactly the scan yeah got that thanks rob sure okay now once you resolve uh what we try to do is that we cannot always depend on only one software uh saying that okay it has given us some result we will have to take uh different opinions of different softwares to mathematically also assess that okay what we are getting is actually from uh the same but celestial object and not a noise so that's where we try to take from various uh methods of gathering data and then if they are all able to give you the same result saying that at around 1.2 you are getting a peak then you can trust it's just that you know you don't trust the software just because only that software is giving you data that's how we are trying to do and this is how we wanted to assess ourselves that our signal was right so this was one method okay so now i think that was the introduction about the solar um radio telescope that we had done uh so if you have any other doubts do please ask me i'm trying to go into the next one uh which is talking up about the hydrogen line detection is there any questions on the solar part okay so now i'll try to go into the hydrogen line um telescope that we have built uh detection telescope that we have built uh before i go into that uh just trying to give a small introduction about uh why is it so important about this hydrogen line detection and what is the physics behind this whole thing so hydrogen line detection uh is is about detecting the neutral hydrogen neutral hydrogen is a form of hydrogen where it was formed during the dark ages and the transient from dark edges to epoch of rear theory of i'll just go to the next picture which is much more clearer uh for a while there was uh there was nothing um and then the max mata started coming together uh that is where we have hydrogen which is the most um abundant element uh started getting into the ionization phase where it can start it it can start getting itself binded into molecules then getting into helium and so on and that actually started the star formation galaxy formation and and the whole uh wreck of the um of the universal uh big bang part plus the reionization part now here's where the hydrogen line detection becomes very very important because this neutral hydrogen is those is part of those primordial matter of in interstellar medium i'm sure professor uh singh can you explain much more he being a cosmologist uh but if i'm going wrong please do correct me somewhere but that's the uh that's where it becomes very important to detect this as this this forms the primordial part of the universe big magnification itself and then when you are detecting something like this it means that you are going far far far back in time and that's why it is so important they are doing a lot of research on this because it gives you uh so much back in time and also this particular telescope is also described as a weighing scale for the universe because once you detect hydrogen hydrogen is the most abundant element and out of the total universal mass i think five percent is only the periodic matter which is the matter which we can all see where stars are made out of we are all made out of rest of it is dark energy dark matter and so on so the 95 percent is a a lot of unknowns are there but this five percent of what is known uh is where a lot is derived out of uh h1h1 of the hydrogen line physics so um now what many of us in astrophotography is instead are interested most of the time is also in the visible part where we look at the hydrogen alpha that is visible but h1 which is a neutral hydrogen which is an atom which is made out of only one electron and one proton which is as much dependent as much abundant as any other uh is not detected using any of the visual means but it can be detected using the uh radio nodes so what happens uh is actually uh if you look at this diagram where there is a blue sphere and the red sphere there uh the blue sphere being the uh proton and where the red sphere is the electron which is moving around the protons and there is sometimes what happens is there is a spin flip spin flip which happens where you're seeing uh both arrows are pointed here in the upper direction if when a spin flip happens there is a flip of the electron where the arrow gets pointed towards the downward direction that happens because of various things i'll think but not get into that part so once it happens this is this particular instance a photon is released and that is what is uh released in form of an energy and that is what is released at 1.420 gigahertz that is what is called as the hyperfine line of hydrogen and that is that can be detected here from earth and that is what we are interested in and that is what this radio telescope is all about one fine line photons released uh in that manner do they have any specific color no color this is not detectable by optical okay but uh if we were to get image or something using some software would that show any color for us actually no uh that's because uh neutral hydrogen [Music] does not have rather i don't know you can add some false color maybe but uh it is not optically this is not detectable okay so actually the energy which is released at that point of time uh can be detected only through a radio means and that that is not converted into we saw in the first slides the optical uh is at a much more much much kind of you know lower uh frequency bandwidth or the wavelength is much shorter but i can't but i think that one can do false solving for them yeah false coloring is possible once you get through radio you can do a false coloring okay but yeah yeah that's steve now i'm just trying to go uh once again um just to get into a bit of our details about why it is so important now um this uh this picture on the left is about the whole nature timeline itself starting from the big bang um down at the bottom in the dark ages and then start and then where the vertical breaks and earlier steps are formed in much more recent history from the universal point timeline point of view but what we are interested here is after the dark ages um there is where the earlier stars and the earliest galaxies and so on were formed and here is where the epoch of re-ionization though a lot of matter which was in the dark ages started clumping together um why is still a question which is answered yet to be answered in much more detail i feel is it true for when you're saying so in the why it happened it's still a question which is yet to be answered uh but we know that it happened uh and that is where the epoch of reionization was and here is where most of the hydrogen line physics is dwelling on or that's where we detect most of these lines from that means whatever you detect using this telescope you are touching something which is so primordial um that's the that's the kick that or or the thrill that somebody gets when you actually detect something out of it um yeah so for when the sinks sir you want to add something about from from the hydrogen line part on the cosmological point of view i think yeah it could be good i think i think he's got some connectivity issue but this is a very interesting discussion here so i just want to go back to the topic of the electron spin which you mentioned there which you mentioned that it might have many reasons when the spin happens but here you also mentioned that the photons are emitted because of the spin right yeah but in normal circumstances the photon generally gets generated the electron jumps from one band to the lower band yeah is that the same correct it's the same if you see this diagram i'll just flip back to the previous slide you can see the hydrogen energy levels diagram here yeah yeah yeah so this is a visible part you know the you see that the electron is jumping to the lower energy levels this is the hyperfine line where n is equal to one okay the visible is that dynamically mostly but there in the visible spectrum we do not mention anything of the front spin right it's more of a jump from one band to the other band yeah it is it is because of already it is in the excited state we are talking about neutral hydrogen and that is not a neutral hydrogen that uh most of the beta okay okay okay so in case of central uh hydrogen it is the spin that actually emits the photon character spin flip that image at spin flip is because of quantum physics and quantum mechanics okay uh fine so next uh i'll just go to the next slide now now that was the uh basic background of uh why this whole thing is so important and uh and that's why it makes it also important to build something and and do some trials yourself and that was the whole idea that i worked along with sri lanka who's also there and uh have to build this so we started building something which is very nascent naive and in the early days uh where we just used a small dipole antenna where we converted uh the 21 centimeter into uh when you convert that frequency it's 1.4 gigahertz and then the wavelength is 21 centimeter so we went with the half five half dipole design and then we started building a dipole with a reflector and started playing around with a lot of design uh to arrive at the best antenna there are many many ways to isolate and detect this hydrogen line our idea was to build something which is portable because typically the observatory scale or even where some university students who do all these kinds of projects they use uh horn antennas and they use a dish antenna and so on now the horn antenna is when you try to build them each one of them is around four and a half to five feet which is massive and then and the dish antennas are also one meter to three meter to five meter to 20 meter they're all very very massive structures now when you have to uh use them uh and at home and then you'll have to do some physics coming out of it uh one is the budget constraint next is the power next is the time uh what we have with us and what we wanted to do is something portable where you you can let it carry it around and place it on wherever you want and mostly which you can carry it in a shopping bag a normal shopping bag which you can carry it around and it's lightweight that was a few parameters that we had in mind and that's when we started experimenting on on building with those fundamental parameters and that's how we have been trying to improve so with that philosophy so uh what we have tried to do uh i i'll just show this is the dipole with the reflector behind and then you use a a coaxial cable and it goes through uh instead of a normal white band lna we are using a a hydrogen line filter a sawtooth filter which is used specifically for hydrogen line detection and analysis this is a start to filter which is available from new elec uh company and that is what we have used and then paired it up with an rtl sdr uh and then rest of the software and so on is the same it is just that the antenna design here is the most crucial thing and plus the usage of the filter um i have just gone to the next slide where you can call it as the mark one of our design uh this was the mark one of the design which we did and we did some analysis on what is the signal strength and characteristics of the antenna that we have built uh this was built using um kind of a dipole uh this dipole is look and see is something if you have seen old black android tv sets and you would have got an antenna with it it looks very similar and what we have used as a reflector here is a caked in um what is generally used for baking so that's a tin which we used which is made out of aluminium and that we use as a reflector and this is the conducting elements uh those those were the first designs that we did uh we were able to detect something uh but the resolution and then this uh and this pen were not that good uh and from then on we have been making various trials to make it better and better and uh still the trials are on and something which we built uh i just showed when we started just like that okay let me ask a question for the reflector do we keep a gap of lambda by 4 that 50 mm which you have mentioned yeah so if everything it depends upon upon the design so know whether you want to keep it again that you want to have in all that parameters i'll come to that once again later i have a small uh topic on what we need to do to make the design better okay okay please please carry on sure uh yeah this is uh this is just a picture which shows uh our journey of what we have done um the pictures down below uh where there's a rectangular plate which is once again a big ink ray and we we hooked up a small dipole there and that was our first design and then we put up another once again using a reflector which is a baking tray but this time we used uh this is a bike one we built a bike-wide antenna this is a completely different kind of a design uh of using a bike ride this had got its own distinct advantages this is good as well and then during the early days of may we built a new design which is the strip parabola um design with with the casa grain kind of a feed in front and once again a bike ride feed so now if you look at the picture top on the top left corner this is the whole setup um you you just place a computer um so i just kept some plastic chair and the stool just to get to the eye level and then hooked it on to a normal tripod this is very very light this whole thing does not weigh more than 120 grams or something and it goes easily in a in a back shopping bag and on the extreme uh right um just behind those uh flowery background is a new design that we have built just once again carrying forward the strip parabola element but we have built a completely different uh reflector and director with the cassegrain feed which is you know 45 degrees of axis with the base reflector and it still resists as an antenna it still uses the um antenna here so all this is made out of normal aluminium sheets uh actually what i did to build them was use most of these baking cans flatten them um cut them and place it in front in in a in a shape of the parabola and then put them together but uh for us to design this whole thing it has taken a lot of time and effort to get to uh the right um we can say the characteristics uh right from s11 to vswr to um to finding out the right gain um the finding out what is the right beam width which you require and so on it took a lot of permutation combination for us to get to this um so that's the that's some of the journey that we have done and the newest one which is on the right side with the flowery background is if you can see on the red color is nothing but the ioptron sky guide pro uh this is on a tracking mount uh this whole uh thing uh is less than around it's around 620 grams so it can easily sit on a sky guide a pro kind of a mount and it can keep tracking the object i can shut off the mount and make your make the celestial object flow through the uh flow through the antenna and we can do a various combinations with this and that was the whole idea for us to build this so that's the whole background of how we have built that now i'll try to show a video once again um to show how this works um the audio i don't think is required now what is there on the screen over here when i switch on the video you can see it's uh it's already tuned to one point four two zero four zero five right so that's where most of the hydrogen line gets detected at that frequency and i will just start the video now if you see the video there is a waterfall here which is in in between so you see the waterfall it starts getting horizontal lines that means the waterfall is getting disturbed and then in down below you start getting some pulses there you are seeing those pulses uh so those are the pulses which we are getting when we move the antenna across the sky i'll just show you in the same video when you move the antenna across the sky uh there is a variation in the amplitude of the signal and you see the antenna is getting moved across the sky and this was the place where we were moving where typically uh the the milky way is seen yeah so and when you move it across the sky you should be able to get those information or pulses coming in from the milky way and that is what we are trying to detect uh in this radio telescope so that's the basic operation and uh if you have questions on this uh i can take it i'll show what we do out of this in the next few slides okay this one talks about once you get a signal this was the uh this was the software which is used to get a signal you can see uh there is a sorry keep the point on okay you can see um from the baseline uh there is a peak which is getting uh jotted out and then it also gives you on the db meter uh what is the signal strength and so on and then if you look at here um there's a yellow portion which denotes the peak signal and the signal bandwidth itself and then the blue portion is the kind of the waterfall which is kind of got disturbed because the amplitude is varying and down below you can see this is how it normally looks when you are away from the object and when you start pointing towards the sky where there is a celestial object which has got a neutral hydrogen which is typically here uh the galactic and you start getting those pulses there now what you do is that you do have record option of taking information all that is seen over here in the in the mathematical ascii dump and this is how it looks like it's just a simple ascii file and then you store this and then you do a lot of uh analysis and out of this and that's what we are trying to do there are few things that you can do out of this uh one is uh we want to find out uh the rate at which uh the arms of the milky way are knowing red shift and blue shift and so on we cannot actually find out uh at what rate that we are expanding um and then we can do a few other things which you are planning to do i just stopped here for a while sheeran you want to explain uh yeah sure so from this data we can analyze various things that is like for example the first thing is like what is the velocity which the cloud that we are observing is moving so once we are pointing this telescope towards the source the source would be the hydrogen cloud which would be present in the milky way bank so once we are observing that that must also be moving with respect towards so there are a lot of other calculations that we need to do first of all we can calculate the shift whether it is moving away from us or coming towards us so that will give you the red shifter concept from that we can calculate its velocity but after that there are certain uh calculations based on the geometry so once we do that we exactly get the velocity with which it is moving so that is one part that we can do then once we have the velocity at different locations then we can try to plot a graph which is also known as a rotational curve which will give you the mass of the galaxy so right now we are at eight kilo pastry from the center of our galaxy so it will give you the mass of the galaxy under eight kilo pascal so the mass that we are going to calculate from this graph would we got to know about dark matter so this was the experiment which told us that our galaxy or other galaxy that are present contains certain amount of matter which is not normal which is having some different characteristics but this was the experiment and the first experiment to tell the presence of that matter still there are lots of other researches going on on this actually i have a question yeah [Music] is your device is applicable for other galaxies too or or it can only measure the rotational curve of our galaxy the milky way so right now for our telescope the beam width is uh very much low so so with this the resolving power of our telescope is also valued as per now it can only detect the mass of our galaxy but once we improve that then we can also target some other galaxy okay but this is this is the general application of this device yeah correct okay so uh the rotational curve what happens in the rotational curve is the plot of velocity with the distance and here the distance is the distance from the center of our galaxy so as we move away from the center what happens is in the general form if we look at the catalyst equation the velocity should be reduced but this is not happening once we study the rotational curve the velocity is getting constant so this difference between the velocity told us that there is somewhat relation between the mass and the velocity so uh the cloud which are at the exterior part of our galaxy are being hold up with a force that is pulling it towards inside so that that force needs to relate with some of the mass so that is that that's where the concept of that matter is so right now we are at the stage where we are just testing this we have uh tested it with uh observing the sun we have also tested the design for getting the various parameters the velocity the red ship and uh still we are working on improving that improving the resolution so that we can get the actual exact count and once we get that then we will be going yeah so is there any calibration thing in this device for example you are measuring the rotational curve of a milky way for example so yeah how you can get then get the idea that that rotational curve is correct okay so before plotting the rotational curve need to know what is the velocity with which we are moving which is also known as the velocity of standard so that is one part where we need to calibrate because everything is moving with respect to another so we need to first fix the uh the frame of reference with which we are calculating it so here the frame of reference is between the galaxy and the velocity with which the sun is moving around the galaxy which is indirectly the velocity of standard local stress so that is that is already being calculated which is around 230 kilometer per second but i recently just a couple of days back that also was changed so with the recent uh radio telescope observation and we are also moving with a greater speed but in our calculations we have considered 240 kilometers per second so once we get that once we get closer to that then we can do the rest of any more questions no thank you thank you i have a good question is the field of view of this telescope and how do we actually assess it how we can determine the field of view we i will show i will show the i will show some pictures and also some calculations that we have done later in the slide but uh what we are looking at is a beam width of 22 degrees so it means that the field of view will be around 22 degree okay okay there are certain calculations as well to thank you for uh being with on the field of view as well as you can also try that in simulation by if we have time yeah once again yeah we did the same kind of an assessment as what we did in case of the solar one which i just explained uh we took a series of spectrograms here uh trying to assess where we are getting the peak and uh then uh software and then we um then we analyzed it and that is how this this graph down below is plotted and um this this gives some idea about when you detect something you see those spikes over here and those spikes are kind of interpreted as the signals which are coming in from the source and that's how uh we were able to do the basic detection and and then do a cross analysis of what we have detected is actually right and and so on okay i'm just coming to kind of what components are being used uh there is a this is the rtl sdr which is the sdr software defined radio it is made by various companies what we have used something from rtl there is also something which you can get from movalec and various other manufacturers as well so uh they they work from uh 24 megahertz to or 2 400 megahertz that's their bandwidth and then um this talks about the input impedance it is around 50 ohms and so on but uh there are another digital conversion capacities around 8 bits and that is what we have used plus there's also those two filters that we were showing earlier uh what we are used for hydrogen line filters uh is a softer filter from uh that's one on the left of the blue color background and then there is a white band lna this is used as a low noise amplifier just to amplify the incoming signal and then feed it to the rtl sdr um that's what we these are the two devices that we have used from the electronics point of view rest of of the antennas we had to do some modifications to get them right this is the antenna design basics i will not go too detail into it but just to uh give a very brief introduction is that uh now here's where uh like like the field of view what promise signing up was asking uh about the dream bit uh it tells what is the what is the kind of resolution that it can do uh when it when the device is pointed towards a source and how long can that source be held in its view so it all depends upon the beam width uh characteristic and then and the main load where you actually start gaining a lot of data uh from the source which is emitting the signal so this beamwidth becomes very important when you are trying to design an antenna itself so it depends upon various parameters right from the aperture of the antenna and then the orientation the design that you are following and what kind of antenna what type of antenna you are doing and so on but there are a few um formula which is used for calculating the beam width and trying to resolve it to a particular frequency that you are interested in and then it will give you what is the benefit in our case it was around 1.72 degrees for the parabolic fish that we use for solar patio telescope it means that it cannot hold the sun for more than 1.2 degrees in the uh when it moves across uh in 1.2 degrees it moves away that means that the sun signal is lost it's a very narrow band uh now it's in terms of the chromosphere so you need to keep adjusting the antenna when the sun is moving to keep receiving the same signals constantly so that's something that is what is uh shown as as as the net result of when you calculate the beam width and find out how effective your antenna is so this is something which is very important and then we did a lot of simulations using a software like matlab and uh then cst and then there is vipreldi and many other software tools like uh net2 and so on uh which you can use to simulate your design and find out before actually building the antenna how effective it is uh in terms of uh of resolving a particular bandwidth or or a particular source or or a signal strength what what would be your game when you use a particular physical or a geometric pattern you design an antenna so this is just a snapshot of what we did using matlab and we started calculating the beam width and uh and baseband characteristics for the basic hydrogen line telescope when we built the mark one version so this has been further further improved a lot uh to narrow the beam width and try to get to a main loop which is much more which has got gain uh part of radio telescope design the antennas yeah these are the few parameters which you need to keep in mind one is the bandwidth that means what is that band that you want to operate between and then radiation pattern and beam width gain polarization and directivity i try to touch upon each one of them very very briefly um so bandwidth is is is where the upper and lower frequency bands that a particular signal is emitted say for example you want to build a an antenna which captures all the fm radio signals so fm radio typically operates between 89 megahertz to around say megahertz so that's the bandwidth in which this whole thing needs to operate and that's the that's the fixation of the bandwidth uh that you want to resolve an fm radio signal and you want to design an antenna for it i'm just giving an example and that you keep in mind and then you start designing something and then you'll have to find out what is the radiation pattern um so a radiation pattern is in which the antenna transmits or receive the signal and what is the pattern it follows and so it's a function of uh you know a main lobe and a back lobe and there are side lobes the main lobe is is actually the major portion in which all your signal reception or transmission happens and this the gain of this determines the net gain of the system itself then you will have to find out the this is the main this the radiation pattern in which the maximum radiation gets uh either converges or diverges towards the source in which it is transmitting or receiving so i think we don't have to put too much into detail otherwise it will go into antenna theory and so it just keeps this and then of course we were just talking about the beam width there are two subdivisions once again the full power and sorry half power and a personal gain which talks about what is the maximum resolution that can happen and with respect to a particular gain and yeah and where it is where is the peak in which your total resolution gets dissolved i will not put too much into all this so next is the directivity and gain directivity is uh when we're looking at the solar part where we are seeing that whether it is offset or it is a central focus depending upon on the directivity it means that whether it needs to be directed towards the source or it is offset direction or the gain talks about the net volume at which the signal is received when it is i think we can continue it in next lecture because it is too fast i'm just trying to tell that you can build various types of antennas okay okay it's saying that you don't have to limit yourself to a particular design for a particular application and you have various because there are various interesting things in this talk so yeah i don't want that you move it so fast all right so we can also discuss this in our next session stop presenting yeah that was the idea today um sorry if i think i'm about yourself also so you can it can be included in the video okay my name is naam i'm a software in india and astronomy is one of my hobby and radio xiaomi is something that we wanted to try new and that's a new avenue which we have been exploring what we can do as as a hobby from the radio parts of the astronomy and that's how we started a year and house back to do a couple of projects and still in the process of building uh and perfecting those designs getting started for building the reception of sun's chromosphere observation and then 21 centimeter hydrogen line detection these were the two home built radio telescopes that we have been working on and that's the short introduction my name is [Music] so it was a private observatory and then after i came to bangalore where i meet ra and then we all started with this right now told you so basically apart from this i am also looking for my master's ready and i have got two acceptance from australia right now so i will be continuing that once the orders are open until now i am just doing all this kind of research [Music] [Music] for this wonderful talk and thanks shirang thank you for bearing i think it was wonderful because generally we talk about astrophotography so definitely a bit overwhelming for one session and definitely we all realized that but uh looking forward for the next session quite interesting and quietly possible i don't think you know we can grasp all the elements in one go but it's a great uh introduction to the field and we are very proud of having you in our forum in astronomy forum having known you i think it's a great honor for they have certainly added a new dimension to astronomy yes absolutely absolutely um thank you thanks for organizing this thank you thank you so much for inviting me thank you thank you okay thanks to all thank you all thank you so much good day thank you

Channel: AstronomyLive

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Length: 95min 46sec (5746 seconds)

Published: Sun Nov 29 2020