What is the purpose of a guard band between channels?

• A. Increase channel capacity
• B. To prevent adjacent-channel interference by providing spectral separation
• C. To reduce noise floor
• D. To increase modulation order

Answer: (B)

Guard bands create a buffer of unused spectrum between channels so their signals stay separate. In real systems, filters aren’t perfect and signal spectra have side lobes that can spill into adjacent channels. The guard band gives room for those skirts to attenuate and for any out-of-band emissions to die away before the next channel begins, reducing adjacent-channel interference. Guard bands don’t increase capacity; they actually waste spectrum. They also don’t directly lower the noise floor or increase modulation order.