 One of the things that amateurs do is space. It's quite common for amateurs to have small portable radios that won't work well over urban distances with buildings in the way. So we put repeaters on the tops of tall buildings. Well, a satellite's just like a really, really, really tall building. And so right from the beginning of the space age, as early as December 1961, amateurs have been putting repeaters into orbit. It turns out that amongst a bunch of communications engineers working for NASA in the early 60s were a bunch of hams. So you need payload. You need ballast for this particular payload so when you launch a rocket it's got to be spin symmetric otherwise the thing will fail to launch greatly. So there's the payload and there's often ballast to get the thing to balance correctly so the rocket will maintain a steady path. And so they're like, huh, you need ballast and we would like to put a repeater in orbit. And so really right at the beginning of the space age you've had amateurs doing this. So there are still about, today there are about 15 amateur satellites in orbit. Satellites that carry amateur traffic, some have another function like the International Space Station for example has human beings inside. But it has an amateur repeater on board, an amateur sort of email system and also an amateur station. So if you have the right gear you can in principle talk to astronauts on board the ISS. The difficulty here is they all work London time so you've got to be willing to do it at very odd hours of the morning and I haven't yet succeeded. So to deal with all the current amateur satellites they're all in low earth orbit. They will cross the sky from horizon to horizon quite quickly. Who are accustomed to seeing a TV antenna on the side of a building, not in Singapore. The satellite is pointing in a fixed direction. That's pointing at a satellite 36,000 kilometres away. Almost four times the diameter of the earth, so the earth satellite, very long way away. Much cheaper satellites orbit lower and all the amateur satellites are as cheap as possible and so they orbit quite low. The problem with that is that it's moving. And so yes, it did camp last year, Adrian and myself. Initially I was just holding the antenna and operating the radio at the same time, which was exhausting. So at some point Adrian could go pointing the antenna so I could operate the radio. Again, because the satellite is moving so quickly, about 20,000 kilometres per hour it's affected ground speed. Doppler effect actually changes the, measurably changes the frequency of the radio signals. So you're having to adjust the radio continually as the satellites cross the sky. So I thought okay that's really much too difficult. The obvious and simple solution to this problem is to build a device which will take care of the pointing, which is that thing there. And so that actually works. So the deal is there's really four things that you've got to worry about, at least four things with the satellite. One is that they are crossing the sky so you've got to point. One is that the frequency is shifting with Doppler shifts so you've got to keep adjusting the radio. And one is, again, amateur satellites are cheap so they don't have attitude control. They just tumble through space. And so the antenna's orientation changes continuously and unpredictably. So in addition to pointing, I was also twisting for Adrian. I was twisting to keep it correctly aligned with the satellite. So when you make a machine to do it, that third one's a bit difficult. And it's actually cheaper and simpler to just add a second antenna at right angles. And it's a bit, one more trick which we'll get to to make that work. But that's why it's two sets of antennas. The antennas are also at two frequencies to keep the receiver and transmitter from interfering with each other. Usually on the ground with ground better repeaters you have things called cavities with big brass tubes. On a satellite, weight is everything. And so it's actually cheaper and simpler to have the receiver at a lower frequency and the transmitter at a higher frequency so they can't interfere with each other. The transmitter won't cause the receiving antenna to resonate. And therefore it's much easier to keep the receiver and transmitter from interfering with each other by having the two radios of two different bands and also the antenna's are running. And so that's why the two different sizes of elements of the antenna. So the design I chose was produced by Agilio Disclavir to Work for NASA's Classroom Access program. So this is a program to make it easier for K-12 students to get access to space-related stuff in different ways and in particular to communicate with satellites. And so I thought, OK, I'll try his design. It's a fairly, well, it's a non-3D printing based design. It turns out to matter. I've forgotten all the metalworking I learned in high school. So his design uses mostly robotics parts. And as you can see they're pre-machined. So you're buying standard parts and putting them together. Give or take things like the cut around the brass tube in the middle. It's a sort of really rough cut. That's my extremely clumsy metalwork. This took about 10 or 12 iterations of cut, assemble, examine, dismantle, cut a bit more, assemble, examine. Nope, miss that? OK, dismantle. Do it again and again and again until I've got it to the point where all the moving parts work together correctly. What you're seeing is on its side, the two metallic cylinders of the motors. So the thing to the right is actually the azimuth motor, the motor that turns that way. It's inside the box on top of the stand. The motor at the top is the azimuth or elevation motor, which turns that way to point between the antenna and overhead. That's on the left, on the symbol machine. What you can probably see is a green board. They're actually printed circuit board. So this is an interesting way to attach a potentiometer to be a sensor. To make a very simple servo, you have a DC motor with a reduction gear and a bit of geometry. Instead of using steffans and then having to know where the thing is with limit switches. So it's just, it works. The plastic gears are only for positioning the pots, they're not load bearing. The load bearing stuff is all metallic. So this is from ServoCity, which is a robotics part supply in the US. The parts are designed for industrial and other robots. The white pipe is where you attach the antenna. There was a problem. This was the design for a single antenna. The guy who designed this thing updated it later for two antennas. The elevation motor is at one end and the thing attaching the antenna is this bit of white pipe sticking out the side. In the updated version there's actually two metal pipes and the elevation motor has been moved out to one side. So I was working through this and you can see how the two green arrows there handmade quarter inch to one inch places with set screws inside tubing. I'm not even mentioned in the text. I don't even know what that means. Let alone have the technical skills of the parts to make such a thing. So that, right, that's kind of a showstopper. Really need the two antennas otherwise the fading is horrible. If you only got one antenna and you can't twist it, which in the single antenna case you can't, half the time you can't communicate with the satellite. So I looked around Hacker Space and I had some PVC pipe. And so that's why it looks like that. It's a bit rickety. If I, after it's all operated and you'll see it, it does do what it's supposed to do, but it kind of wobbles around a bit. If it's out by a few degrees it doesn't matter. But it's a, this is quite a nice sort of tight assembly of robotics part. So this is a hastily assembled PVC pipe. The fully assembled set looks like that. Which is more or less what you can see over there. I'll call out. I'll just come back to the details later. The key thing I suspect that suggests at this point is the, the means of control is a USB cable. And again there's a change in the design which led to a rather strange and a lot of work which I'll explain in a minute. The fabrication was, for me a bit of a learning exercise. I've never done surface mount soldering before. And so there's a bunch of resistors and capacitors there that are surface mount. Everything else is through hole. There were just the capacitors that were tiny at all. One milliliter by one and a half milliliter of devices. So I ordered from element 14. You can see two syringes there. On the left is a grey one which contains the solder paste. Which turns out you're supposed to use an air compressor to deliver, not use a hand. Really, really, really hard to get the solder out at all. Pressing away. The hands are hurting to get pellets of solder out. On the right is another syringe containing the tack flux. So this is flux as the flux built into solder, but it's also sticky. So it's useful to put a bit down to sort of cause the component to stick where you want it to stick. Before the solder melts, once it melts, there's enough surface tension to get the component to sort of jump into the right position and then the solder will set again. But until then there's a risk of it moving around. Especially because for the smaller group of components I decided to use a hot air gun instead of an oven. The other reason was we didn't have an oven. So, frequently the hot air gun, which is the thing on the right. So you add the little tube you hold, which blows air up to 300 degrees Celsius. Keeping all the components in place with the tack flux and pointing the other right way is an interesting exercise. Roll up one tape in the back. If you put one component in place and then you want to do another one, it's like, ah, shrew a hot air is such that it will actually re-melt the solder and push the component away. So the cap on tape is actually enough to stop that from happening. I'm pleased to say it developed during the Apollo program for space use. More for near zero Kelvin use, but it also has interesting properties for soldering. The tack flux has dire warnings on it about it being an irritant. Which is why the duct and the fan, nonetheless, I got a whiff of the stuff up my nose in my eyes. It is really, really unpleasant. Like, sort of lindiment, but much stronger and just nasty, nasty stuff. Not toxic, not hugely dangerous, but really, really irritating. So, things to be aware of. If you see this stuff, like a tube that says in big letters, it says in MSDS the material safety data sheet first, and follow the instructions. The more sensible approach is indeed to use an oven, and the cheap way is to take an ordinary office shelf toaster oven. In fact, we now have one ad-hacker space earmarked for this purpose, and build a microcontroller. Don't use it for bread. Yeah, no longer food state. No, not appropriate for food, but put a thermal probe, a temperature sensor inside the oven, or rectifier to switch the thing on and off, and then there's firmware available that can be fed the temperature profiles for different solders. Different solders have different optimum peak temperatures, rates of heating, rates of cooling, and the amount of time they held at heat. So you say, yes, okay, I'm using that solder. Here's the profile, give it a controller, and it'll do the exact thing that that solder is designed to have done to it. So this is for 12 components, looking by hand, was fine, but for a larger number, and at some point I will do this, the radio end of this is interesting. So there are two different tricks here. This is very much amateur radio tricks, use of quarter wavelength sections of coax. So one of the problems I mentioned was to solve the twisting problem is to have two antennas at right angles to each other. That's not quite enough. You need them offset by quarter wavelength. So you can either physically offset them, which makes the mechanical design much harder, or you can insert a quarter wavelength difference in the feed line. So the signal from or to the radio, I'll get to the loop in a moment, but you can see that the two end pieces are about the same length, they go to the antennas, and there's a bit of cable in the middle. That is exactly one quarter wavelength at the speed at which a radio signal propagates inside this piece of coax, which is not quite the same as this bit of line of acumen, but similar. And so it means that whatever is put into the antennas or received from the antennas from one is a quarter wavelength behind the other. And what that does is creates, they call it circular polarization, but it's more accurately a sort of helical, it's like a helix in space. So instead of being that way or that way, it's that. And the important property that has is that will resonate with an antenna at any orientation except pointing at you. But at one position there's nothing we can do, so the signal is all going away from the earth. But in every other orientation, a helical polarized signal will resonate. And as I said, amateur satellites are cheap, so they don't have good attitude control or any attitude control. And so the two antennas plus the quarter wavelength of the way solves that problem. Two separate harnesses, this is the 70 centimetre one, but there's also another one with a bigger loop pieces for the two meter. The other piece is the loop, and here you have more amateur tricks. So connect two 50 ohm antennas in parallel and you now have a 25 ohm mode, which does not correctly match the radio, which expects 50 ohms. So how do you transform 25 ohms to 50 ohms? Well you can make filters and stuff with transformers, or you can go, special trick with transmission lines, if you are assuming everything else is correctly balanced, the, if you have a 25 ohm feed, a 50 ohm feed and a bit in the middle, that's the square root of the product of the two of the outside, the geometric average, then it will actually transform one to the other. So what you need to get from 25 ohm back to 50 ohm is a piece of 37.5 ohm coax. Well you can't get 37.5 ohm coax, but you can get 75. So the loop is actually two bits of quarter wavelength, 75 ohm coax in parallel, to make a single piece of quarter wavelength, 37.5 ohm coax, which transforms 25 ohms to 50 ohms. So how to do dirt cheap, and very light weight, both the circular or helical polarization, and the transformation to get from two parallel ohms and is back to what the radio expects with just its coax. There are other tricks that can be done with quarter wavelength coax. It's quite remarkable what average is going on. So I can use that for... I won't bore you with it. Another detail, unfortunately, between the publication of the instructions and the kit that I purchased, the thing had been revised. This never happens. In particular, the use of the USB cable creates a little bit of space for interference to arise, which is fine for Morrison voice, but it's a problem for packet radio. There are some digital modes that amateurs use that are fairly narrow compared to a white one. And the guy doing this wants to do packet. So he switched to using a pair of X-beads. I don't mind spending a bit of money, but it's like, really, I'm going to buy two X-beads, replace a cable? That's ridiculous. I'm not going to do it. So the original board, it's easy on a green board, which is the new one. You can see the rectangles of hard white edges. Those are actually transistor pairs that form H-bridges for running the two motors all backwards. So you have a set of four transistors to run a DC motor one way or the other. And then there's a little driver chip by the button below. On the older board, you can probably make out the mounting points for the transistors on either way and the driving chip. But at the bottom, what is actually a USB socket for the mounting point for it. And next to it, a driver chip to match serial to USB. Right. I'm sitting in a hackerspace on a Saturday. How do I fix this? I looked around, I've got a USB cable, but it's a USB to GDL. And the microcontroller on the board expects 3.3. There's got to be a solution to this problem. And of course there is. I had a bag of 10k resistors. So I was like, right. How can I shift 5 volts to 3 volts? Well, like that. And I don't need to go the other way. The other board at the moment doesn't have a feedback channel. It's only commands going to it. But if I wished to go the other way, then one driver on resistors would be enough. So for the way that I did go, which is to bring the 5 volts down to 3.3 before going into the microcontroller, you can see the outline of the actually position on the board and then a little bit of the rear board that I sort of cut off and soldered for resistors to and a socket for the USB cable. And voila! I have the input on the front of the board there. Thank you. Sort of working stuff out as I go. So that was most of it. The other problem was the metalwork. It's fiddly and time-consuming and it's stuff I haven't done since high school and frankly I spent 20 hours on it. Had I understood that beforehand I would have taken a different design which I'll talk about in a moment. There's another problem and it's common to rotators. The device, how am I going to talk about that? The device has 360 degrees of azimuth freedom which is great to be able to point to any one direction. But if you're wanting to follow a satellite across the sky it might pass you zero. So for example, assume the satellite is crossing the blue line on the left and so your initial azimuth limit is vertical. So you can point here to here. So your satellite is crossing and suddenly you hit zero degrees. So now you've got to turn the whole machine this is the red line the other way and take a minute or so and of course the satellite is still moving. So you're out of communication for a couple of minutes and then reconnect it before it disappears below the horizon. This is not really a satisfactory solution. The fix is you decide before the pass where you want your zero to point and the software supports either north or south which covers most satellites. You turn the thing around you set a setting in the software and hopefully it all works. So that's really awful. So I'm inclined to look for a 540 degree freedom device there around and one of the options I'm looking at is sat-nawx. So a more contemporary not NASA attached open source project is working on a network of ground stations. In addition to running the network they also publish far more contemporary designs so apart from simple aluminium channel cut with a hacksaw all the complicated parts are 3D printed. So there's no hours of cut and fit and fiddle and cut and fit and fiddle and cut and fit and fiddle is just put the bits and go. So that's, I will consider that especially if it's easy to modify it for 540 degrees. The other thing is having to have a laptop sort of on a tripod next to it, it's stupid. So I use this single heavens above on my phone don't yet know how but wouldn't it be nice to be able to say I can select a satellite and tell the tracker to follow it. So maybe. The addition of a digital compass and gyro to deal with 619 degrees of freedom so I don't even have to worry about correctly guessing orientation, just plonk it and let the computer whack it out but what I really want to do is eliminate the rotator completely and instead do something called beam forming. This is a vastly more complicated approach but the chips are doing it are getting cheaper and cheaper and cheaper so maybe. So the idea is if you take in this case 6 antennas in a straight line this is a simple case a phased array and you are sending the same thing to all of them but you send it a bit earlier to the one on the right and then a bit later and later as you go to the left you end up with a coherent wave front not going down the picture but going to the right that is to say you can control the direction in which the signal is being sent not by rotating an antenna but by manipulating the phase relationships between the signal arrival at each of the antennas and so instead of having arrays of antennas on non-rotators the idea is to have a bunch of non-moving antennas unfortunately it is a larger number of antennas in radios but the radios themselves are sort of incomplete radios they are front ends of radios and a lot of computation are then complete like 400 radios so that it then becomes possible to communicate with amateur satellites both send and receive without having to have a moving thing in the first place what will invalidate all of this is that not quite invalidated but certainly another option is that in January QTEL, the Qatar Telco is launching a geostationary satellite and so far it appears that the Qatar Amateur Radio Club will get to write a transponder on that satellite all the way to geostationary and then a US satellite later next year so this hasn't been the case for decades we're now back to okay let's put ameters not at 500km but at 36,000 so anyway stuff to play with for some considerable time to come thank you