Signals and modulation

How information is put onto a radio wave and taken off again.

What modulation isPutting information onto a carrier wave.Amplitude modulation (AM)Varying carrier strength: sidebands, bandwidth and efficiency.Frequency modulation (FM)Varying carrier frequency: deviation, capture effect and noise immunity.Single sideband (SSB)Dropping the carrier and one sideband for efficient HF voice.Digital modulation: FSK, PSK and QAMHow bits become tones and phase shifts.Bandwidth, symbol rate and data rateHow much spectrum a signal needs and how much it can carry.Error detection and correctionParity, CRC and forward error correction.Spread spectrumDirect sequence, frequency hopping and why they resist interference.Time domain, frequency domain and FourierSeeing a signal as its sine-wave ingredients.Sampling and the Nyquist limitTurning a continuous signal into numbers, and aliasing.