Why should the phase of a PSK signal be changed at the zero crossing of the RF signal?
To minimize bandwidth✓پاسخ درست
To simplify modulation
To improve carrier suppression
All these choices are correct
توضیح
Reversing phase at the instant the RF waveform passes through zero avoids an abrupt step in instantaneous voltage. A step is a discontinuity, and discontinuities spread energy widely in frequency, so timing the transition at the zero crossing keeps the occupied bandwidth to a minimum.