Practical takeaway
Modulation chooses how information changes the carrier; multiplexing chooses how multiple information streams share the available channel.
E8B · Amateur Extra question group
Modulation & Multiplexing
Modulation chooses how information changes the carrier; multiplexing chooses how multiple information streams share the available channel.
Amateur Extra exam focus
The explanation below teaches the ideas behind E8B while keeping the important terms recognizable. The Quiz Me button uses the current question-pool wording for this group.
1. Modulation index describes depth of modulation
In AM and angle-modulation systems, modulation index relates the information amplitude to how much the carrier is varied. Excessive modulation can create distortion or unnecessary bandwidth.
2. FM bandwidth depends on deviation and modulating frequency
Larger frequency deviation and higher audio/data frequency both increase occupied FM bandwidth. Deviation ratio compares peak deviation with the highest modulating frequency.
3. Multiplexing separates by time, frequency, code, or orthogonal carriers
TDM assigns time slots, FDM assigns frequency ranges, and OFDM sends data on many closely spaced orthogonal subcarriers.
E8B checklist
- Modulation index describes how strongly a carrier is being modulated.
- FM bandwidth grows with deviation and modulation frequency.
- TDM separates by time; FDM by frequency.
- OFDM uses many orthogonal subcarriers.
Exam scope: NCVEC 2024-2028 Amateur Extra Class (Element 4), effective July 1, 2024 through June 30, 2028, with February 4, 2026 fourth errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool