Questions about Radio Systems

[Silicon014]

Hello guys! I'm embarking on a project which requires me to have an intimate relationship and knowledge of radio transmission, because I'll be designing a system from scratch. Could someone explain the process to me technically, from start to finish (I mean like from eletrical input to antenna efficiency)? I'd honestly like to know about not only transmitting, but also on receiving transmissions (tips and tricks appreciated! ). It'd be great if you were a HAM radio operator or someone of the like, as I really intend to have a deep understanding of the entire system. Thanks a ton!

[K^2]

What's your background? But basically, you need to understand how every part of a superheterodyne works to understand radio communication.

[Silicon014]

Well, basically, what I'm doing is designing the radio system for a bit of a dream project of mine. I'm actually planning to design a satellite from cheap, off the shelf components that serves a very important purpose (Which I will not say to protect my uncopyrighted intellectual property). I will say that it needs to be able to send signals that can reach the Earth over about 50000km of vacuum (Near GEO)

[sharpspoonful]

I'm a Radio Operator in the military. What you are looking to do will be difficult depending on what you intend to broadcast. First off, you will need to broadcast in the UHF band or higher; since you won't have a relay of satillites, you'll need to know its orbit angle, velocity and position in the sky to transmit properly. There's a lot to the transmission.

Sorry I sound like potato. I'm at work and using my phone.

Edited November 8, 2013 by sharpspoonful

[Silicon014]

No big deal Sharp. Is it really that tough to make an omni-directional or a dipole radar transmit that far of a distance?

[Bunsen]

The big questions are (1) how much information do you have to move and (2) how much electric power can the satellite spend on its radio. If you're talking about a cubesat-scale thing, which usually goes along with the cheap, off-the-shelf components, transmitting from beyond GEO down to Earth is going to be very hard.

[K^2]

Sharp's right. If you simply broadcast a signal from 50,000km, there won't be much to receive due to inverse square law. You have to be able to focus it into a beam directed at Earth, or wherever your receiver is, and that means working with UHF or higher.

If you want that beam to be steerable, it has to be a phase array. These things are way more advanced than a regular radio. If direction can be fixed, you just need a dish.

And like I said, what's your background? How much do you actually know about electronics, because this isn't something you are going to do from a blank slate. If you are serious about it, and you don't have much in terms of starting knowledge, you'll have to start with books and probably some classes. I can point you towards some resources, but I need to know what you are starting with. How much do you know about electronics, general physics, and mathematics.

[pxi]

It might actually be worth looking into seeing if you can do a HAM Radio Licence course, that would probably teach you a lot of what you want to know.

[NGTOne]

I actually looked into building a CubeSat myself - based on the research I did, your available electrical power (on the order of, if you were lucky, about 20 watts) wouldn't be enough to run an omnidirectional transmitter that could actually get picked up against the background static. Best bet would be two dishes of some sort, one on the ground, and the other on your sat. I'd wager that the one on the ground would have to be rather large (think something along the lines of an old-school satellite TV dish).

And keep in mind that even with cheap, off-the-shelf components, a CubeSat project will cost you on the order of roughly 80-100K. Anything more custom than that will likely push your costs higher.

[Nibb31]

And putting a CubeSat in GEO is going to cost a lot more. I don't even think there are any upper stages with provisions to carry CubeSats to GEO.

[K^2]

And putting a CubeSat in GEO is going to cost a lot more. I don't even think there are any upper stages with provisions to carry CubeSats to GEO.

There are. And I've seen quotes as low as $30k for a cubesat launch. It's pretty reasonably priced.

based on the research I did, your available electrical power (on the order of, if you were lucky, about 20 watts) wouldn't be enough to run an omnidirectional transmitter that could actually get picked up against the background static.

You can do bursts. Dish won't do you much good on a cubesat. Since you are limited to 10cm on the side, even if the dish folds out, you'll have hard time getting something over 30cm in diameter. That's a 1GHz wavelength. Even at 5GHz you'll be lighting up a 10° cone. You can work with that in LEO, but from GEO you are doing hardly better than omnidirectional broadcast.

Point is, if you want to "talk" to something in GEO, you need a much bigger sat.

[Winter Man]

A good book that's been handed down in my family is this:

Worth a read if you can find a copy. It predates transistors, but the principles are all the same. Also for the purposes of aiming a signal on a cubesat you have more than just wireless comms issues. You need to think about satellite orientation as well. Even the biggest dish won't do you any good if it's facing the wrong way. Although on the dish side of things, I recall seeing somewhere an inflatable dish like a half-metalised balloon. Those things could be really quite huge and pack down to not all that much.

[JebidiahsBigSister]

Could someone explain the process to me technically, from start to finish (I mean like from eletrical input to antenna efficiency)? I'd honestly like to know about not only transmitting, but also on receiving transmissions

No they can't.

They can't because, unlike KSP, real life science takes time and effort in which to become proficient. I would estimate that if you wish to have an "intimate relationship and knowledge of radio transmission, because I'll be designing a system from scratch." it would take 200 - 300 hours of study in order to begin to accomplish your goal. Several people have recommended books to you - I might also recommend the latest version of "The Radio Amateurs Handbook".

There are no "tips or tricks" which can be relayed to you to accomplish your goal other than providing you with source material with which you can study.

I'm actually planning to design a satellite from cheap, off the shelf components that serves a very important purpose (Which I will not say to protect my uncopyrighted intellectual property). )

In order to do that you will need roughly a Masters (or possibly a Bachelors if you are extremely bright) in Electrical Engineering requiring 4-6 years of study. Attempting to to what you wish without such an education is just a bit ... unrealistic would be a nice word to use.

Edited November 8, 2013 by JebidiahsBigSister

[DaveofDefeat]

Not to mention if hes building this himself hes going to need to know how to code and some basic computer systems.

And will space radiation and the temperature effect the electronics at all?

Edited November 8, 2013 by DaveofDefeat

[nhnifong]

If the goal is to make observations from beyond GEO but GEO itself is not a requirement, consider an eccentric orbit that brings the sat closer to the surface at it perigee so it can periodically communicate with a ground station.

[Kryten]

If he's thinking of a secondary he can't be terribly picky about orbits. I think most slot providers don't actually offer a choice at all, other than 'take it or leave it'.

[hotmailcompany52]

In order to do that you will need roughly a Masters (or possibly a Bachelors if you are extremely bright) in Electrical Engineering requiring 4-6 years of study. Attempting to to what you wish without such an education is just a bit ... unrealistic would be a nice word to use.

Not nessciarley all you need is some advanced computer coding knowledge. All you need is a raspberry Pi and some science stuff and a way to transmit and yor done

[NGTOne]

Not nessciarley all you need is some advanced computer coding knowledge. All you need is a raspberry Pi and some science stuff and a way to transmit and yor done

Not quite. A RasPi isn't radiation-hardened - over time, cosmic rays striking the silicon chips will cause errors and damage, culminating in component failure.

[K^2]

If the goal is to make observations from beyond GEO but GEO itself is not a requirement, consider an eccentric orbit that brings the sat closer to the surface at it perigee so it can periodically communicate with a ground station.

That's a good idea. Molniya should do the trick. It has a period of exactly half of sidereal day, meaning it can be right overhead at lowest approach once in every two revolutions, and its apogee is at 40,000km. That's a touch short of the OP's 50,000km, but maybe that's good enough.

By the way, I mentioned earlier that there are relatively affordable cubesat launches, but I should have pointed out that it's for LEO. GEO is not going to be as cheap. Though, there was a project for a cubesat with a tiny ion drive. That could get to GEO or Molniya from a LEO launch.

[sharpspoonful]

Another issue I would like to present is frequency allotment. I dont know where you are in the world, but in the US you'll need to buy an FCC licence to operate which is expensive. UHF and SHF they are not cheap and the equipment for SHF isn't cheap either.

[NGTOne]

That's a good idea. Molniya should do the trick. It has a period of exactly half of sidereal day, meaning it can be right overhead at lowest approach once in every two revolutions, and its apogee is at 40,000km. That's a touch short of the OP's 50,000km, but maybe that's good enough.

By the way, I mentioned earlier that there are relatively affordable cubesat launches, but I should have pointed out that it's for LEO. GEO is not going to be as cheap. Though, there was a project for a cubesat with a tiny ion drive. That could get to GEO or Molniya from a LEO launch.

There are commercially available electric and monopropellant thrusters built for CubeSats - problem is, they don't produce a lot of thrust (naturally, right?), and they all need a 3U sat for any appreciable fuel/payload ratio (some don't even fit into a 1U unit).

[Bunsen]

Another issue I would like to present is frequency allotment. I dont know where you are in the world, but in the US you'll need to buy an FCC licence to operate which is expensive. UHF and SHF they are not cheap and the equipment for SHF isn't cheap either.

That depends on what you're doing with the satellite. If it's not in support of somebody's job (and the FCC is now starting to count university research projects as somebody's job), you may be able to operate under an amateur license. As for the universities, the FCC now wants them to apply for experimental licenses -- more paperwork than ham, but still not the expensive commercial licenses.

If you aren't under the FCC's jurisdiction, though, I have no idea.

[NGTOne]

There's another thing as well - GEO, believe it or not, is regulated by the international community (specifically, the International Telecommunications Union). This is to prevent geosynchronous sats from, you guessed it, interfering with each other's radio signals (or smashing into each other). Any other orbits are fair game, though.

[dharak1]

Does that mean you could put it in half day and be fine? I thought GPS sats used half day? What if you interfere with their signals? What is the OP using this sat for? I hope its pictures of Earth, that would be neat.

[K^2]

problem is, they don't produce a lot of thrust

I don't think of that as a problem. Once you're in LEO, you have all the time in the world to get to the orbit you need. What you really care about is ISP. So if there is a good commercial option for a high ISP ion drive, then it's doable.

But if it has to be a 3U, that's going to roughly tripple the launch cost. Then again, since 1U would probably be too small for this mission anyhow...