The classic AM transmitter layout is a master oscillator, followed by a "pen", or penultimate amplifier, followed by a PA or power amplifier. The master oscillator, which is probably crystal controlled, generates the carrier frequency.
In FM the carrier is still present and the power is still there, at a constant amplitude at the transmitter. It's only the frequency of the carrier that alters, in time with the audio applied to it. The louder the sound the further the frequency shifts.
The process of changing the amplitude of the "carrier" so as to add information to it (modulation) doesn't change the frequency of the carrier. But it does create energy at two other newfrequencies.The new frequencies are equal to (carrier frequency) plus and minus (the modulating frequency). These are referred to as the upper and lower sidebands.The upper sideband is an exact copy of the modulating signal, but with every component of it shifted up by an amount equal to the carrier frequency. The lower sideband is a mirror image of the upper sideband, with every frequency component in it reflected about the carrier frequency.
In a analog transmitter the RF carrier have to be modulated with the analog signal either by AM or FM where in digital transmitter the carrier is simply switched on and off a off = a zero and on = a one
FM transmitter : In this case the frequency of a carrier signal is modulated/altered in accordance with that of frequency of modulating signal. TYPES OF FM TRANSMITTER: 1> directly modulated FM transmitter. 2>indirectly modulated FM transmitter. an FM transmitter is a portable device that plugs into the headphone jack or proprietary output port of a portable audio or video device, such as a portable media player, CD player, or satellite radio system. The sound is then broadcast through the transmitter, and plays through an FM broadcast band frequency. Purposes for an FM transmitter include playing music from a device through a car stereo, or any radio.
1AnswerA coherent detector uses the knowledge of the phase of the carrier wave to demoduleate the signal.it's simply a product device , which multiply the AM signal by a sinusoidal signal having the same carrier frequency , followed by a low pass filter ( LPF). The product will shift the AM signal to 0 Hz and double carrier frequency , and the LPF will eliminate the later component.2ANSWER:Coherent detectioninCoherent detectionrequires carrier phase recovery at the receiver and hence, circuits to perform phase estimation.Sources of carrier-phase mismatch at the receiver:inPropagationtalking causes carrier-phase offset in the received signal.inThe oscillators at the receiver which generate the carrier signal, are not usually phased locked to the transmitted carrier.coherent detection: Huge need for a reference in phase with the received carrierinLess complexity compared to incoherent detection at the price of higher error rate.Coherent ( synchronous ) detection: in coherent detection , the local carrier generated at the receiver in phase locked with the carrier at transmitter .Non coherent ( envelope ) detection : this type of detection does not need receiver carrier to be phase locked with transmitter carrier
The oscillator circuit, which is usually quartz crystal controlled with the quartz crystal in a temperature regulated oven to stabilize its resonant frequency.
it generates the carrier frequency of the output after passing a signal.
-- the modulation index varies -- the instantaneous deviation varies -- the amplitude of the carrier component varies -- the spectrum of sidebands varies -- the total occupied bandwidth varies
In FM the carrier is still present and the power is still there, at a constant amplitude at the transmitter. It's only the frequency of the carrier that alters, in time with the audio applied to it. The louder the sound the further the frequency shifts.
The process of changing the amplitude of the "carrier" so as to add information to it (modulation) doesn't change the frequency of the carrier. But it does create energy at two other newfrequencies.The new frequencies are equal to (carrier frequency) plus and minus (the modulating frequency). These are referred to as the upper and lower sidebands.The upper sideband is an exact copy of the modulating signal, but with every component of it shifted up by an amount equal to the carrier frequency. The lower sideband is a mirror image of the upper sideband, with every frequency component in it reflected about the carrier frequency.
The frequency with which the carrier frequency is deviated is exactly the modulating frequency, i.e. the frequency of the sound that makes up the music or voice announcement, stereo pilot, SCA subcarrier, etc.
Low frequency signal are not able to get propagated throught longer distance. So it is to be carried by a carrier wave. Hence high frequency carrier wave is to be generated by the help of an oscillator. So we need an oscillator here a crystal oscillator to produce high frequency carrier waves.
In a analog transmitter the RF carrier have to be modulated with the analog signal either by AM or FM where in digital transmitter the carrier is simply switched on and off a off = a zero and on = a one
If you subtract from the carrier frequency the frequency of the tone that modulates it, then filter out the carrier frequency, then you have a lower sideband frequency. If you add to the carrier frequency, filter out the carrier, then you have an upper sideband frequency.
FM transmitter : In this case the frequency of a carrier signal is modulated/altered in accordance with that of frequency of modulating signal. TYPES OF FM TRANSMITTER: 1> directly modulated FM transmitter. 2>indirectly modulated FM transmitter. an FM transmitter is a portable device that plugs into the headphone jack or proprietary output port of a portable audio or video device, such as a portable media player, CD player, or satellite radio system. The sound is then broadcast through the transmitter, and plays through an FM broadcast band frequency. Purposes for an FM transmitter include playing music from a device through a car stereo, or any radio.
A carrier wave is produced by an electronic oscillator that generates a steady waveform at a specific frequency. This waveform serves as the base signal on which information is modulated for transmission in communication systems like radio and television. The carrier wave's frequency determines the bandwidth and reception quality of the transmitted signal.
In a analog transmitter the RF carrier have to be modulated with the analog signal either by AM or FM where in digital transmitter the carrier is simply switched on and off a off = a zero and on = a one