In pulse position modulation (PPM) the position of the pulses shift right or left depending upon the amplitude of mod. s/g.

The o/p of the PWM modulator is used to trigger mono-stable multi vibrator. The multi vibrator goes into high state when triggered by the negative edge of pulses, stays high for pre-determined period of comes back. This results in positional variations.

1] PPM can be demoulated only when synchronized.

2] By standing synchronization pulses from $TX^r$ to $RX^r$, the pulse generator gets synced.

3] PPM are given to SR flip-flop.

4] O/P of pulse generator is given to set i/p, if sets the flip flop & Q goes to high.

5] The o/p of PPM, i.e. pulses are applied to reset input of SR. flip-flop, it resets the o/p.

6] Thus PWM o/p is obtained which can be converted to analog using PWM demoudlator.