Radio Fundamentals🔗
Everything an antenna, a feedline, or a receiver does comes down to a few ideas about signals: how fast they alternate, how long each wave is, and how strong they are compared with something else. This topic covers that theory, the radio-specific part of the Basic exam's sections B-004 and B-005.
It starts where Start Here leaves off. The electricity underneath, from voltage to capacitors and inductors, lives on Exploring Electronics; these articles link to it rather than repeat it.
1. Describing a Signal🔗
- What Is a Radio Wave? Frequency, Wavelength, and the Spectrum — AC set loose from the wire, wavelength as 300 divided by megahertz, the ITU bands from MF to UHF, phase, and harmonics
- Decibels: Ratios You Can Add — why 3 dB doubles power, how chains of gains and losses add, S-units, and antenna gain in dBi and dBd
2. Coils and Capacitors🔗
- Reactance and Impedance: How Coils and Capacitors Treat Each Frequency — reactance in ohms, why a choke and a bypass capacitor stop RF but not audio, and impedance as the total opposition to AC
- Resonance and Tuned Circuits: Picking One Frequency Out of Thousands — where the reactances cancel, series versus parallel, bandwidth, and antenna traps