E8D02: Direct sequence: What spread spectrum communications

Q: What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?

The correct answer is B: Direct sequence. The correct answer is B: Direct sequence. Direct sequence spread spectrum is the technique that uses a high-speed binary bit stream to shift the phase of an RF carrier. The binary stream (spreading code) directly modulates the carrier phase, spreading the signal across a wide bandwidth. In direct sequence spread spectrum (DSSS), a high-speed pseudorandom binary sequence (the spreading code) is used to phase-shift the carrier. This spreads the signal energy across a wide frequency band. The receiver uses the same code to despread the signal. DSSS is widely used in systems like Wi-Fi (802.11b), GPS, and some amateur spread spectrum modes. The high-speed code creates the wide bandwidth characteristic of spread spectrum signals.

Updated: Dec 9, 2025 | Source: 2024-2028 Question Pool | Topic: E8D

E8D02E8D

What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?

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Deep Dive: E8D02

The correct answer is B: Direct sequence. Direct sequence spread spectrum is the technique that uses a high-speed binary bit stream to shift the phase of an RF carrier. The binary stream (spreading code) directly modulates the carrier phase, spreading the signal across a wide bandwidth. In direct sequence spread spectrum (DSSS), a high-speed pseudorandom binary sequence (the spreading code) is used to phase-shift the carrier. This spreads the signal energy across a wide frequency band. The receiver uses the same code to despread the signal. DSSS is widely used in systems like Wi-Fi (802.11b), GPS, and some amateur spread spectrum modes. The high-speed code creates the wide bandwidth characteristic of spread spectrum signals.

Why Other Answers Are Wrong

Option A: Incorrect. Frequency hopping rapidly changes the carrier frequency, not the phase. It doesn't use a binary bit stream to shift phase. Option C: Incorrect. Binary phase-shift keying (BPSK) is a modulation method, not a spread spectrum technique. DSSS uses BPSK as part of its operation, but the spread spectrum technique itself is direct sequence. Option D: Incorrect. Phase compandored spread spectrum isn't a standard term. Direct sequence is the correct answer.

Exam Tip

Direct sequence = Binary stream shifts phase. Remember: Direct sequence spread spectrum uses a high-speed binary bit stream to shift the phase of an RF carrier, spreading the signal across a wide bandwidth.

Memory Aid

**D**irect **S**equence = **B**inary **S**tream **P**hase **S**hift (think 'DS = BSPS')

Real-World Example

You're using a direct sequence spread spectrum system. A high-speed pseudorandom binary sequence (maybe millions of bits per second) phase-shifts your RF carrier. This spreads your signal energy across a wide frequency band. At the receiver, the same code is used to despread the signal, recovering the original narrow-band information.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E8D

Reference: FCC Part 97.3

Key Concepts

Direct sequence Spread spectrum Phase shifting Binary bit stream

Verified Content

Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E8D topic.