In this project, one could design the terrestrial receiver that will be able to hear signals coming from the Sallesat I. Furthermore, that represents the educational part of the satellite, intending an approach to all schools and universities of the world on radio communication through an educational kit.
The double finality of this project requires the use of an efficient receiver as simple as possible with components easy to find on the market at a very low cost.
The work started from zero, studying what kind of integrated circuit should be used on it. There are several ICs on the market that have almost all the functions required by the receiver, so a careful analysis of the sizes, costs and distributors was needed. Finally, the Motorola MC3362 was selected. The selection of this IC was due to the fact that this chip allows a double conversion receiver type (and it would save us a lot of external components as for example the mixer), has a DIP format easy to solder in place and can be easily found on the market at very low cost.
Then, we started to make the first prototype. This process was divided in three phases:
RF Amplifier + Filter
Integrated Circuit MC3362 that includes two mixers, IF amplifier, demodulator and IF filters, squelch and audio frequency amplifier.
As we got the expected results, we then started to design the printed circuit board using the software Protel as a working tool.
In the final design of the board several factors were taken in consideration, as the common ground, minimal size, and etcetera. Further to this, several components were replaced, specially the coils that now will be supplied by Coilcraft, because the work of winding the wire on the coil’s forms were too difficult for students without any previous experience on that.
The resulting project can be seen on the photographs shown at the left (from up to down: receiver diagram, front view and rear view). The receiver has an on/off switch, squelch control and a volume control on the front panel that includes the speaker, while the output for a modem, the antenna connector and a third one for the power supply connection will be on the back.