Self-clocking Signal - Analog Examples

Analog Examples

Amplitude modulation – modulating a signal by changing the amplitude of a carrier wave, as in:

is self-clocking, as the zero crossings serve as a clock pulse.

One may consider this clock pulse redundant information, or at least a wasteful use of channel capacity, and duplex the channel by varying the phase, as in polar modulation, or adding another signal that is 90° out of phase (a sine wave), as in quadrature modulation. The result is to send twice as many signals over the channel, at the cost of losing the clock, and thus suffering signal degradation in case of clock drift (the analog equivalent of bit drift).

This demonstrates how encoding clocking or synchronization in a code costs channel capacity, and illustrates the trade-off.