Goal
Recover the message from I/Q and compare demodulation methods.
Prerequisites: Parts 02–06. We finish SSB generation with the phasing method after Part 08.
Future lessons
- CW — telegraphy: a narrow filter, a beat frequency oscillator (BFO) for audio beats, the keying envelope, and key clicks from hard switching.
- AM — amplitude modulation: envelope detection and synchronous detection; detuning and overmodulation.
- FM — frequency modulation: phase difference, instantaneous frequency, deviation and the units of the result.
- SSB — single sideband: USB/LSB, detection by multiplication; an overview of the filter, phasing and Weaver methods.
Lab plan
- Compare a telegraph element with a rectangular envelope and with a smoothed envelope.
- Build a model of an AM transmitter and receiver and compare two detectors.
- Recover FM with angle(z[n]·conj(z[n-1])); check the units and the ambiguity of the phase step.
- Receive test USB/LSB signals; after Part 08, compare the generation methods.
We do the experiments in Python with NumPy, SciPy and Matplotlib. We keep the parameters, units and plots. The base models use float64 and complex128; we add bit-depth limits in separate experiments.
Completion criteria
- I can explain which signal property each demodulator uses to get the message.
- I compare the original and the recovered message and take gain and delay into account.
Result for the main project
Demodulators and repeatable experiments with transmit and receive.