Radio Communication and Electronics Fundamentals (RO/RM trade)
Radio Communication and Electronics Fundamentals (RO/RM trade)
This trade domain tests basic electricity, radio propagation, modulation, transmitters/receivers, antennas and operating procedure. Expect numerical items on Ohm’s law, power, wavelength and decibels.
Core rules
- Ohm’s law and power: V=IR; P=VI=I²R=V²/R. In series, current is common; in parallel, voltage is common.
- Wave equation: λ = c/f, with c ≈ 3×10⁸ m/s. Convert MHz to Hz before dividing.
- Modulation: AM varies carrier amplitude; FM varies carrier frequency. FM resists amplitude noise better but needs wider bandwidth.
- Propagation: HF (3–30 MHz) supports skywave via the ionosphere; VHF/UHF are mainly line-of-sight.
- Decibels: for power, dB = 10 log₁₀(P₂/P₁); 3 dB ≈ double, 10 dB = tenfold.
- Receiver/antenna: sensitivity detects weak signals; selectivity rejects adjacent channels; SWR near 1:1 shows a good impedance match.
- Procedure: use standard phonetic alphabet, clear call signs, and correct RST signal reports.
Worked example
Find the wavelength of a 150 MHz signal. λ = c/f = (3×10⁸ m/s) ÷ (150×10⁶ Hz) = 2 m. The mistake is to divide 300 by 150 and forget the unit: 300/150 = 2, but only because MHz and m/s are paired as λ(m)=300/f(MHz).
Traps
Confusing frequency with wavelength; using 3×10⁸ km/s; treating dB as a linear unit; swapping AM and FM; assuming SWR measures radiated power; and mixing series/parallel resistance rules.