Industry Videos

Physical Data Transmission - Part 2: Amplitude Modulation & Frequency Shift Keying

The video introduces basic physical‑layer modulation, contrasting simple line codes with two more capable schemes—amplitude modulation (AM) and frequency shift keying (FSK). It explains why line codes waste bandwidth, carry few bits per symbol, and struggle on shared or non‑dedicated media, prompting a shift to modulation techniques that map data onto carrier waves. Key concepts covered include frequency versus wavelength, the inverse relationship between them, and the rule‑of‑thumb that signal power roughly halves each wavelength traveled. Higher frequencies yield more symbols per second (greater bandwidth) but suffer rapid attenuation, while lower frequencies travel farther but support fewer bits. AM is described as varying carrier amplitude to represent binary states, illustrated with a vacuum‑tube circuit and modern transistor equivalents, though it is rarely used for digital data due to noise susceptibility. The bulk of the lesson focuses on FSK, where each binary value is assigned a distinct frequency. Bell 103, a historic modem standard, uses four tones—1070 Hz and 1270 Hz for the calling station, 2025 Hz and 2225 Hz for the answering station—allowing full‑duplex communication. The presenter emphasizes a 200 Hz channel separation to avoid intermixing of sidebands, a principle still relevant in contemporary modem and fax designs. Understanding AM and FSK provides a foundation for modern, higher‑order modulation schemes that build on these basics. Designers must balance frequency‑driven data rates against range limitations, and the legacy of Bell 103’s tone‑based FSK continues to influence today’s error‑resilient communication protocols.