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Pulse-position modulation - Wikipedia, the free encyclopedia

The advantage of using PPM for this type of application is that the ...Pulse position modulation is also used for communication to the ISO/IEC 15693 ...

Question:PPM Pulse Position Modulation : "The amplitude and width of the pulse is kept constant in the system. The position of each pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave. PPM has the advantage of requiring constant transmitter power since the pulses are of constant amplitude and duration. It is widely used but has the big disadvantage that it needs a synchronization between transmitter and receiver." 1) what does it mean by "The position of each pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave?" 2) What does it mean by synchronization i.e "the big disadvantage of PPM that it needs a synchronization between transmitter and receiver" ? thanks

Answers:The transmitter puts out a stream of pulses called sync pulses which the receiver recognizes, in a special circuit called a phase locked loop(PLL). In the PLL it has an oscillator that generates pulses at about the same frequency as the transmitter (The frequency of the sync pulses is known ahead of time by standards.) a circuit called a phase detector decides whether the local generator is putting out its synch pulses at the the right frequency, it adjusts the oscillator to make it right. then it makes sure that the phase of the local pulses is adjusted so that the local sync pulse arrive exactly at the same time as the transmitted ones. This is known as being in synch. . in between each of the synch pulses, the transmitter will generate a data pulse,.These pulses do not confuse the PLL because they do not have exactly the same time between them. The receiver will will clear and start a counter when it receives a synch pulse and read it when it receives the data pulse. the value in the counter is passed through the receiver as the received data. Therefore the delay between the sync and data pulse conveys the value of the data to be transmitted. Clearly, I have oversimplified things a bit. periodically, systems have some housekeeping data they add to the data streams that make the data link more robust. and things like parity and error detection and error correction codes are sometimes sent with the data.

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Answers:It's more resistant to noise than AM. It requires less bandwidth than FM. It's harder to encode/decode than both.

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Answers:From and audiophile's point of view, less distortion and a richer sound. From a radio tech's point of view, less atmospheric interference and lower incidence of bleed-over onto adjacent frequencies.