Electronic Fundamentals and Equipment
This domain tests the electronics behind station equipment: semiconductors and biasing, power supplies, op-amps, digital basics, test equipment and safety. Advanced questions often ask you to calculate a bias point, a gain, or a dissipation and then judge whether the component is operating safely.
Semiconductors and biasing
Diodes rectify or regulate; a zener diode operates in reverse breakdown to hold a reference voltage. A BJT has a base-emitter drop near 0.7 V and current gain beta; an FET is controlled by gate voltage and has high input impedance. Bias networks set the operating point, while emitter or source resistors stabilize it against temperature and device variation. RF power devices need heat sinks, neutralization and suppression of parasitic oscillation.
Power supplies and filters
A transformer steps AC to the required level; a bridge rectifier converts it to pulsating DC; a filter capacitor smooths it; a regulator holds the output. Ripple is reduced by larger capacitance and higher frequency. Switching supplies are efficient but generate noise that must be filtered and decoupled. Fuses belong on the hot side, and safety ground must never be defeated.
Op-amps and digital basics
An ideal op-amp has very high gain and input impedance. Negative feedback sets the gain: inverting gain = −Rf/Rin; non-inverting gain = 1 + Rf/Rin. An ADC with n bits has 2^n levels; Nyquist requires sampling at least twice the highest frequency. Logic families have defined noise margins, and microcontroller clocks can radiate RFI.
Test equipment and safety
A dummy load, wattmeter/SWR bridge, DMM and oscilloscope are standard. High-voltage capacitors can retain charge after power is removed; discharge them safely. RF can cause burns, and transmitting without a load can damage an amplifier.
Worked example
A 12 V supply feeds a 6.2 V zener through 470 Ω; the load is 1 kΩ. Load current = 6.2/1000 = 6.2 mA. Resistor current = (12 − 6.2)/470 = 12.34 mA. Zener current = 12.34 − 6.2 = 6.14 mA. Zener dissipation = 6.2 × 0.00614 = 38 mW. The reasoning: the series resistor drops the difference between supply and zener voltage, and the zener absorbs the current not taken by the load. If the load current rises above 12.34 mA, regulation fails.
Traps
Using the non-inverting formula for an inverting stage; forgetting that an op-amp cannot swing beyond its supply rails; underestimating zener power; using too small a filter capacitor; confusing ADC bits with sample rate; testing a transmitter without a dummy load. A "12 V" transformer secondary is RMS, so the rectified peak is about 17 V - a common power-supply design trap.