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FM also known as frequency modulation is preferred because of the more concise ability to transfer quality sound at the expence of distance. Also FM is not as severely effected by weather as its lower frequency AM counterpart.
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How does a high-power FM transmitter work?
Summary: An FM transmitter has an oscillator that generates the carrier RF signal. Frequency modulation takes place at the oscillator stage. The modulated signal is then sent through some filters and then finally amplified by a class C power amplifier, and then delivered to the antenna. An FM transmitter has an oscillator that generates a carrier signal on a desired frequency. But something like a voltage controlled oscillator is used so that the oscillating frequency can be changed by a modulating signal. When there is no modulation, the oscillator runs at it assigned frequency (called a center frequency). The voltage that is controlling the frequency at which it is running is constant. By applying the volage of a modulating signal to that "controlling" voltage, the frequency of the signal can be caused to vary above and below its assigned center frequency in a way that is directly proportional to the modulating signal. It is shifted above and below its assigned center at a rate proportional to the frequency of the modulating signal and at an amount proportional to the amplitude of the modulating signal. This takes up a bit of what is called bandwidth on the electromagnetic spectrum. The modulated FM signal appears as a "group" of frequencies around that center frequency with the sub-group of frequencies about the center being called the upper sideband, and that sub-group below the center being called the lower sideband. Almost all of the power in the generated signal is carried in these sidebands. This RF signal is them amplified by a high power RF amp, and the (now) high-powered FM signal is then sent via a transmission line to an antenna, from where the signal radiates into space. A link is provided to the Wikipedia article on FM modulation. Surf on over and check out the drawings and the little "moving pictures" to get a handle on FM. (No static at all!)
What is indirect method of FM transmitter?
indirect FM transmitter is the transmitter which indirected connectly to the FMINDIRECT FM GENERATIONWhile it is not possible to vary the frequency of a crystal oscillator directly, it is possible to vary its phase. The resulting PM signal can be used to create FM. This is the basis of the Armstrong modulator.The mathematics required to analyze the Armstrong modulator completely are complex, so we will discuss only the basic circuit operation. An audio signal is passed through a preemphasis network and then an integrator, a special network whose output is the time integral of the input signal. The preemphasized integrated signal is used to phase modulate a crystal oscillator. Mathematically, it can be shown that PM using the integral of the audio signal is identical to FM using the audio signal itself. In this way an FM signal is generated.The Armstrong modulator cannot produce much deviation, so combination of multipliers and mixers are used to raise the carrier frequency and the deviation. The multipliers are used to multiply the carrier and the deviation. The mixers are used to decrease the carrier, while keeping the deviation constant so that additional multiplier stages can be used to obtain more deviation. It is worth going through an example:An FM station is authorized to operate at 90.9 MHz, with maximum deviation of 75 KHz. The FM signal is generated with an Armstrong modulator whose output is 500 KHz with a deviation of 15.432 Hz. The modulator output is applied to 3 triplers and a doubler to obtain a frequency of 81 MHz and a deviation of 2.5 KHz. The 81 MHz signal is mixed with a 77.97 MHz signal to produce a 3.03 MHz signal whose deviation is still 2.5 KHz. This signal is fed through a doubler, tripler and quintupler to multiply the carrier to 90.9 MHz and the deviation to 75 KHz.
Application of pre emphasis and de emphasis?
fm,audio digtal recording
Pre-emphasis in FM systems involves?
Amplification of higher frequency component of modulating signal
What is narrow band FM and how a narrow band FM generate?
If the modulation index of FM is kept under 1, then the FM produced is regarded as narrow band FM. Lower the modulation index, lower the no. of significant sidebands are produced (with reference to bessel function). So lower the no. of significant sideband, lowerer will be the bandwidth of the resulting FM prduced. Sometimes, Narrow Band FM is regarded as, when the significant energy in FM occupies the same bandwidth as ordinary AM with the same modulating signal.
With regard to FM signal modulation how will a decrease in modulation voltage affect the FM signal spectrum?
Answer: A decrease in the audio voltage will resort in a to narrow band and will be difficult for the receiver to detect the audio.
Why is amplitude of demodulated FM signal much less than modulated signal?
because demodulated FM is an audio signal, which the frequency is much smaller that is why it can be transmitted alone. It need carrier which has large frequency. Modulated signal is an audio signal + carrier that is why the amplitude is higher.
What is the need for limiter in FM receiver?
The limiter clips the top and bottom of the FM signal to remove any AM signal or static that was picked up. This prevents the FM discriminator from seeing those unwanted signals and inadvertently converting them to audio, scrambling the intended audio signal. Simply put, the limiter blocks interference and static making FM reception very clean.
What type of modulation is used to carry the picture portion of a television signal?
Amplitude Modulation (AM) is used for the picture portion of a television transmission while Frequency Modulation (FM) is used for the audio portion.
Why power amplifier used in FM transmitter?
Amplifier is used in an FM transmitter to increase the level of a signal suitable for transmission
What is the difference between am raido and FM radio?
A: AM radio is an Amplitude Modulation transmission . Meaning it has fix frequency but it is modulated by the signal. FM Frequency Modulation the frequency is modulated by the signal
Why inTV broadcasting video signal is trancemitted in AM but audio signal is in FM?
AM was used for the video signal because components to transmit and receive the video signal (tubes, originally) were not available that could modulate the frequency fast enough for the amount of information required for a video signal. The VHF band, where most of television broadcasts resided until the the adoption of Digital Television (DTV) was also being used for FM audio broadcasts.
Which type of modulation is used in TV transmission?
In television system for video transmission AM is used and for audio transmission FM is used....
Why FM is used for voice signal?
Analog radio uses either amplitude modulation (AM) or frequency modulation (FM) to carry an audio signal. AM signals can be received at greater distances than FM but they suffer from interference from other stations and a wide range of electro-magnetic sources. FM signals offer better quality with less interference than is typically found with an AM signal. The transmission range is far smaller than AM. For a wide geographic coverage, multiple transmitters are needed although the limited range also makes FM an ideal medium for local stations where long range is undesirable.
Why is frequency modulation preferred over amplitude modulation for transmission of music?
FM provides noise immunity, whereas AM is easily affected by noise. With FM, the amplitude of the sound is converted into a shift in frequency. So the volume is limited by the bandwidth, but the frequency of the sound can vary as much as it likes, giving a higher fidelity sound. Spikes induced on the signal usually affect the amplitude of the signal. The amplitude of an FM signal is not used in the demodulation process and is therefore immune to spikes in the signal. AM was first used in radio because it is very easy to achieve using basic components. A single rectifier only, is needed to recover the audio. FM is quite a complicated process and could only be achieved once electronics had progressed.
Why only AM but not FM used for transmitting video signal?
Because of video's complex nature, AM lends itself to transmitting several different signals simultaneously, like video, chroma, sync, etc. and it can provide the bandwidth required to do it easily. FM for the audio has a bandwidth of 100 khz, and FM is much better for that. It's also a `cleaner signal`, but the FM transmitter has limitations on how much information it can carry.
What does IF mean in an FM circuit?
IF stands for Intermediate Frequency. An intermediate frequency is a frequency which the primary signal or carrier signal signal is changed to in the process of reception or transmission. For example, an FM or frequency modulated radio or FM television tuner uses an intermediate frequency or IF of 10.7 megaHertz, abbreviated mHz. The primary signal of an FM radio may be between 88 to 108 mHz. This signal is processed to 10.7 mHz and then demodulated to an audio signal that human ears can hear. The reason for using an intermediate frequency is that it will not interfere with the primary or carrier frequency. Also, the lower IF frequency is easier to deal with electronically. Commonly used IF frequencies in FM are 10.7 and 5.5 mHz.AM or amplitude modulation commonly uses 455 kiloHertz although others frequencies may be used.
