FM Transmitters and Receivers Questions and Answers

Answer: A

Adjacent-channel rejection is a filtering problem, so steeper skirts at the intermediate frequency are the remedy, usually achieved by cascading more ceramic filters. A quieter front end improves weak-signal sensitivity, which is a different complaint. De-emphasis and audio bandwidth act after detection and cannot separate channels. Matching the remedy to the interference geometry is the recurring discipline of receiver work.

Answer: B

Carson's rule captures about ninety-eight per cent of the power, so the guard band holds the remaining Bessel tail together with any frequency error. The pilot and its harmonics lie in the baseband, well inside the deviation. The receiver's intermediate frequency is a separate matter entirely. And transmitter harmonics fall at multiples of the carrier, far outside the band. Knowing what a guard band is for explains why it is twenty kilohertz rather than an arbitrary figure.

Answer: C

For the same audio, wideband FM occupies 180 kHz against AM's 10, roughly twenty times as much, which is the price of its noise advantage and the reason it lives at very high frequency. Its carrier is not suppressed. Carrying the same audio does not imply the same bandwidth, since FM's deviation rather than its audio sets the width. And the mono transmission is already wide, stereo adding baseband content rather than extra deviation. Quantifying the trade is what makes it memorable.