Name two anti-jamming techniques used in space systems and their underlying principle.

• A. Frequency hopping and direct sequence spread spectrum
• B. Time division multiplexing and carrier squinting
• C. Narrowband filtering and pulse shaping
• D. Antenna cooling and rotor control

Answer: (A)

Spreading the signal over a wider bandwidth is a powerful way to resist jamming in space links. Two classic methods do this in different ways: frequency hopping and direct-sequence spread spectrum.

In frequency hopping, the transmitter and receiver hop the carrier among a set of frequencies in a pseudo-random order known to both ends. Because the energy isn’t staying on a single frequency, a jammer would have to follow the rapid changes or jam the entire hopping band to stay effective. If the jammer can’t track the pattern, most of the transmission lands on a frequency the jammer isn’t interfering with, and the receiver can recover the signal on those clear slots.

In direct-sequence spread spectrum, the data are multiplied by a high-rate pseudo-random code that spreads the signal across a much wider bandwidth. At the receiver, the same code is used to despread the signal, letting the intended receiver coherently recover the data while interfering signals that don’t share the code are spread out and appear as low-level noise. This yields a processing gain that makes narrowband jammers less effective and improves robustness to interference.

Both techniques rely on synchronized codes between transmitter and receiver, and they are central to providing resilience against intentional or accidental jamming in space environments. Other options listed don’t inherently provide anti-jamming benefits: they are general multiplexing or hardware-control methods or picture-in-theory filtering approaches, not spread-spectrum protections.