Physics · Ch 15 — Communication Systems
Detection of Amplitude Modulated Wave
Detection of Amplitude Modulated Wave
Detection of Amplitude Modulated Wave
As the transmitted signal travels through the channel, it gets attenuated, so at the receiving end the antenna's output must first pass through an amplifier before anything else can be done with it. To make further processing easier, the carrier frequency is typically stepped down to a lower intermediate frequency (IF) in an IF stage that comes before detection; a further amplifier follows detection, since the recovered message signal may not be strong enough to use directly. Figure 15.12 shows the overall receiver chain: receiving antenna -> amplifier -> IF stage -> detector -> amplifier -> output.
Detection is the process of recovering the original modulating (message) signal from a modulated carrier wave known to contain the frequencies and . …
What this figure shows. Block diagram, left to right: a simple antenna symbol labelled 'RECEIVING ANTENNA' at top-left feeds down into a horizontal chain of four rectangular blocks connected by arrows: 'AMPLIFIER' -> 'IF STAGE' -> 'DETECTOR' -> 'AMPLIFIER', with the incoming line from the antenna captioned 'Received signal' and the final output arrow on the right …
What this figure shows. Top row: block diagram, an 'AM Wave' arrow into a rectangular block 'RECTIFIER', whose output feeds into a rectangular block 'ENVELOPE DETECTOR', whose output arrow is labelled 'm(t)' leading to 'OUTPUT'. Below, three small waveform sketches labelled (a), (b), (c) sit under the AM-Wave input, the Rectifier output, and the Envelope-Detector output respectively, each with its own 'time' axis: (a) 'AM input wave', a fast carrier wave whose amplitude envelope bulges over one cycle of the message (both positive and negative excursions shown as a hatched oscillating band). (b) 'Rectified wave', the same fast oscillation but only the positive half, so only the upper envelope bump remains (vertical hatch lines under a bulging outline). (c) 'Output (without RF component)', a single smooth sinusoidal hump (the recovered messag …