Satellite Transmitter

[Huma]

I am a student and we are working on a satellite project.

I need help regarding the payload transmitter portion of satellite of frequency 433.9MHz and data rate 256kbps using BPSK modulation technique.

If any relevant link .. kindly inform

[Enthalpy]

Hi Huma, could you tell us a bit more about your project? I built Sara over 20 years ago in a club.

http://www.corsud.net/leau/Micro_satellite_SARA.html

Is this a paper project, or will you build it?

 

What is the available know-how in your team: individually, and as a group? I mean practical knowledge, what have you already done?

 

My first comments:

 

This frequency is for amateur radio. You can use it only if your satellite is for amateur radio. It's also an ISM band but only in region 1 - improper to satellites - and anyway, data transmissions are not ISM. In some countries, for some uses, governmental agencies accept datacomms in ISM bands BUT (1) not everywhere, not always (2) improbably when this ISM band is in a radiocomm band (3) not on a satellite, whose tranmission spreads over a huge area and all around the world. So in case the purpose of the satellite is not amateur radio, you'd better go to a frequency band for satellite communications. We did the error for Sara, it raised worries. Go to you national radiocomm regulation agency, they will tell it clearly.

 

I suggest that you practice the reception of amateur radio satellites.

http://en.wikipedia.org/wiki/Amateur_radio_satellite

This will tell you much more than any book. Do it before you freeze such details like 256kb/s or bpsk. The signal amplitude varies a lot, you want to detect first the carrier despite the unknown direction and the big Doppler effect - so the modulation shall adapt, like low-datarate AM first, and if the signal is strong, bpsk, quadrature, constellation.

 

Do you need to build the transmitters and receivers? The ones on board, the ones on the ground? Buying the ground station (amateur radio bands helps then, sure) save much time, but then your modulation must be compatible. Do you want to build a complete receiver with digital signal processing? Or can you maybe buy the IF+ADC+Processing+software part, and just add the up- or downconverter to the proper frequency? Find a kit, or a detailed description in an amateur paper or book?

[Huma]

Thanks a lot for your response.

First thing is that me and my group members are doing Bachelors in Electronics Engineering and we haven't worked on any communication project till now . So this is our first experience.

Second we are interested in getting such transmitter module which meet our specifications.

And u asked that is this a paper project or will u build it.. we are going to build it .

 

[Enthalpy]

Huma, I know now way of saying that in a pleasant way, it would only be circumlocution... You can't make a satellite without experience.

 

The transmitter is only a small part of a satellite, but already a radiocomm design demands practical experience that takes years to get, and only outside a schoolroom.

 

Buying parts for a satellite is usually impossible, because satellites have some constraints. Not necessarily difficult ones, but unusual. For instance PVC, the cable insulator, is excluded from any satellite design. Or the insulators used at connectors - manufacturers usually won't tell you or just lie. Then you have to cool the transmitter without air. (The often cited radiations, vibrations or reliability are smaller worry). And so on, and so forth. If you buy space-capable hardware, it costs a fortune, for being specially designed.

 

If you buy a transmitter, it will be polluting, and the launch's main passenger will reject your satellite from the flight. Even if the transmitter got to orbit, it would probably fail from bad cooling.

 

You might get an old space-capable transmitter offered, but then you would have all the other difficulties of a satellite. None is so big individually, but they interfere very badly: thermal design, mechanical design, possible materials... It takes people with a broad technical and scientific backgroud to answer these difficulties a consistent way. Big companies have it easier because they build always the same satellite or nearly, and have specialized teams - but this doesn't exist for small satellites, and then you're back to the early space exploration times, when a handful of people must reinvent much.

 

And of course, practical projects are difficult. Every team fails at its first project. Then, at best, it tries again but with a project of more accessible difficulty. Knowledge can more easily be acquired, but a trained team is seldom and takes time. An existing team that has already built a sailboat has far better chances to build a satellite than a group of specialists without individual practical experience nor collective record.

 

I regret the hard answer, but the only way to success is to choose a much simpler project.

 

Since you're in electrical engineering, you might try to build a ground radio receiver for amateur satellites. That would be a (too?) hard project for a (good and big) group. Depending on the time available, just assembling the orientable antenna, connect a commercial receiver (for amateur radio), and possibly steer the antenna by a computer would be a better goal.

 

Just to figure out: half a dozen of well-trained students (not a first project) would take well 3 months of intense work just for that ground station with steered antenna.