Which statement correctly describes DSSS and FHSS in SEW anti-jam capabilities?

• A. FHSS uses PN code spreading
• B. DSSS uses wideband spectral shaping
• C. FHSS uses optimized power control
• D. DSSS uses PN code spreading; FHSS hops carrier frequency; both provide anti-jam advantages

Answer: (D)

Spread-spectrum anti-jam relies on two practical approaches: Direct-Sequence Spread Spectrum and Frequency-Hopping Spread Spectrum. In Direct-Sequence, the data are multiplied by a pseudorandom PN code, spreading the signal energy across a wide bandwidth. This creates processing gain, making a narrowband jammer less effective because it must contend with the signal spread over many frequencies. In Frequency-Hopping, the transmitter rapidly hops the carrier to different frequencies according to a hopping pattern, so a jammer would need to jam across a wide range or track the hop sequence to stay effective, which is much harder in practice. Describing both ideas together captures their distinctive mechanisms and how they each contribute to anti-jam resilience: DSSS uses PN code spreading, FHSS hops the carrier frequency, and both approaches provide anti-jam advantages. The other statements mix up these concepts (FHSS isn’t defined by PN spreading; DSSS isn’t best described as wideband spectral shaping; FHSS isn’t about optimized power control), so they don’t fit as well.