Masat-1 satellite will use the amateur radio frequency band to downlink telemetry data. The downlink data will not be encrypted, so everyone will be able to receive it, decode and process.
Frequency bands employed
- Earth-to-satellite (uplink) on 2 m
- Satellite-to-Earth (downlink) on 70 cm
Satellite’s telemetry transmission frequency: 437.345 MHz +/- 10 kHz Doppler
The reason for the Doppler shift is the orbital velocity of 7-8 km/s, as when a transmitter is getting closer to the receiver the received signal’s frequency is shifted upwards, and when the transmitter is getting away from the receiver the received signal’s frequency is shifted downwards.
The satellite’s modulation scheme: (A1A) CW and 2-GFSK with 625 Hz frequency deviation (CW is clocked at 120 characters/minute, which is well-audible by ear).
Data rate of the 2-GFSK digital packets: 625 or 1250 bits/second (a PC with sound card and demodulation SW is required)
Minimum list of devices required for receiving Masat-1
- antenna suitable for the 70 cm band (in open air, pointed towards the sky)
- tuneable radio receiver with 70 cm SSB USB mode, such as FT-817, FT-897D, TS-2000, etc.
- PC with sound card, running the telemetry packet decoder SW in JAVA environment. The demodulator software can be downloaded from this website.
A minimal arrangement of the receiving station
The structure of a radio amateur station optimized for satellite reception
Timing of reception periods during the normal operation of Masat-1
The digital data packets are transmitted by 2-GFSK modulation, which is a 2-state frequency shift keying where “0″ corresponds to “carrier frequency – deviation”, “1″ corresponds to “carrier frequency + deviation”, but the modulating signal is not square, but filtered by a Gaussian filter (to improve spectral efficiency and reduce leakage). The following figure shows the modulating square signal, the Gaussian-filtered signal and the frequency modulated signal (the bit sequence employed is 010111100010010).
To collect as much data as possible, universities, colleges and enthusiastic radio amateurs are all encouraged to receive our telemetry data and send the captured data to us via the internet.