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What is the purpose of the parallel combination of the resistorand capacitor in the envelope detector? Explain how this part ofthe circuit works

April 23, 2011 by msjaved · 1 Comment
Filed under: Assignments 

1)What is the purpose of the parallel combination of the resistorand capacitor in the envelope detector? Explain how this part ofthe circuit works

2) Common radio uses two modulation schemes-they are AM and FM.Explain very briefly what the FM scheme is. How does it differ fromAM? what are the advantages and disadvantages of each scheme?

3)Which scheme AM or FM has better audio quality? Why?

Solution 2:

The radio broadcasts we hear take place in fourstages.

1. A microphone converts sound wavesinto electrical signals.

2. The electrical signal from themicrophone changes, or modulates, a radio wave called a carrierradio wave, so that it will contain the sound information. Thiscarrier wave is emitted by the broadcast tower.

3. A receiving antenna on a radio tuned tothe proper frequency picks up the carrier wave, which then travelsto the receiver or radio.

4. The receiver detects the modulation inthe carrier wave and converts it back into electrical signals. Theelectrical signals are sent to a loudspeaker, which changes themonce again into sound waves.

Sound information which including pitch andloudness and is carried by radio waves in one of two ways.Depending on the type of radio station AMorFM

the carrier wave is modified differently.Amplitude modulation, or AM, stations code information in thecarrier wave by changing, or modulating, theamplitude,

the height of the carrier wave’s peaks andvalleys. The speed at which the amplitude changes determines thepitch of the sound, and the amount that it changes determines itsloudness.

In contrast, frequency modulation, or FM,stations alter the frequency of the carrier signal. In this case,the speed at which the frequency changes determines the pitch, andthe amount that it changes determines the loudness.

Both these methods of broadcasting radio signals have advantagesand disadvantages.

Generally, AM carrier waves have much longerwavelengths than FM carrier waves, and as a result, they can bendaround obstacles like mountains and buildings better than FM wavesand can travel greater distances before the signalfades.

However, because information is coded in theamplitude of an AM carrier wave, things such as the thermalnoise with appliances and sparks going off in passing cars caninfluence the amplitude and are more likely to interfere with thewave.

Also, any unwanted change in the power of thetransmission can cause an amplitude change that will distort thesound the radio produces.

were in it is much less likely that thefrequency of an FM carrier wave might be accidentally modulated,the quality of the sound is better.

So the FM is better then the AM


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