Practical Circuits
Amplifiers and oscillators
Know the classes of amplifiers: Class A conducts all the time and is linear but inefficient; Class AB is a compromise used in SSB; Class C is high efficiency but nonlinear and used for FM or CW. Know that an oscillator generates a signal and that a crystal provides stable frequency. A mixer combines signals to produce sum and difference frequencies.
Power supplies and rectifiers
Know the half-wave and full-wave rectifier basics. A half-wave rectifier uses one diode and produces ripple at the input frequency; a full-wave rectifier uses two or four diodes and produces ripple at twice the input frequency, which is easier to filter. A bridge rectifier uses four diodes. Know that filter capacitors smooth ripple and that a regulator holds output voltage steady.
Digital and control circuits
Know basic logic gates (AND, OR, NOT, NAND, NOR, XOR) and their truth tables. Know that a flip-flop stores one bit. Know that a microcontroller or microprocessor can control a station's functions. Know the purpose of a relay (electrically controlled switch) and a transistor as a switch.
Worked example
A full-wave rectifier fed from 60 Hz produces ripple at 120 Hz. If hum appears at 120 Hz, suspect the rectifier or filter. If hum appears at 60 Hz, suspect heater wiring or a half-wave stage.
Common traps
Assuming Class C is suitable for SSB - it is not linear. Confusing ripple frequency for half-wave (1×) versus full-wave (2×). Mixing up NAND and NOR truth tables.