modelModulations

Information

The microcontroller writes the character U once (0x55: on air, with its start and stop bits, the frame alternates 0 and 1 at every bit). Its TX pin feeds four transmitters, each joined to its receiver by its own antenna wire and using another modulation. The air data rate is 1200 bit/s, so the drawn carrier is at fDisplay = 4800 Hz (four periods per bit) and the output interval of 10 µs is fine enough to see it.

Plot txOOK.sTx, txASK.sTx, txFSK.sTx and txBPSK.sTx between 25 and 35 ms:

• OOK: the carrier is there for a 1, absent for a 0;
• ASK: full amplitude for a 1, reduced amplitude (0.3) for a 0;
• FSK: 3 periods per bit for a 0 (3600 Hz), 5 for a 1 (6000 Hz), without a phase jump;
• BPSK: the carrier is inverted at every bit change.

Each receiver gets the character (rxOOK.nReceived... equal to 1): the receiver here does not demodulate the drawn signal, it decodes the bit carried by the antenna wire (masked synchronisation, see the user guide).

Components