FM Demodulation | Frequency Modulation Radio Detection | Tutorial
With frequency modulation, the carrier wave phase Φc is shifted Wideband FM has good signal to noise ratio when it's demodulated at the receiver, so it's. Angle Modulation is the process in which the frequency or the phase of the carrier The difference between FM modulated frequency and normal frequency is The amount of frequency shift, produced by a phase modulator increases with. Phase-Frequency Relationship When Frequency is Constant. 0 θ. 0. C t ω θ+ . A Pictorial Way to View the Generation of FM and PM. Phase. Modulator. ∫.
This can be achieved in an analogue fashion as in the case of a transmission like an FM broadcast signal, or it can be achieved digitally to produce a form of transmission known as frequency shift keying, FSK. Read more about Frequency Modulation, FM Wide band and Narrow band FM When a signal is frequency modulated, the carrier shifts in frequency in line with the modulation. This is called the deviation.
The level of modulation is governed by a number of factors. The bandwidth that is available is one. It is also found that signals with a large deviation are able to support higher quality transmissions although they naturally occupy a greater bandwidth.
As a result of these conflicting requirements different levels of deviation are used according to the application that is used. Generally NBFM is used for point to point communications.
Much higher levels of deviation are used for broadcasting.
Receiving FM In order to be able to receive FM a receiver must be sensitive to the frequency variations of the incoming signals. As already mentioned these may be wide or narrow band.
アナログ振幅変復調について DSB-SC/SSB-SC変復調 - サーキットデザイン
However the set is made insensitive to the amplitude variations. This is achieved by having a high gain IF amplifier. Here the signals are amplified to such a degree that the amplifier runs into limiting. In this way any amplitude variations are removed.
In order to be able to convert the frequency variations into voltage variations, the demodulator must be frequency dependent. The ideal response is a perfectly linear voltage to frequency characteristic. Here it can be seen that the centre frequency is in the middle of the response curve and this is where the un-modulated carrier would be located when the receiver is correctly tuned into the signal.
In other words there would be no offset DC voltage present. The ideal response is not achievable because all systems have a finite bandwidth and as a result a response curve known as an "S" curve is obtained. Outside the bandwidth of the system, the response falls, as would be expected.
A common method for recovering the information signal is through a Foster-Seeley discriminator or ratio detector. A phase-locked loop can be used as an FM demodulator.
FM Demodulation / Detection Tutorial
Slope detection demodulates an FM signal by using a tuned circuit which has its resonant frequency slightly offset from the carrier. As the frequency rises and falls the tuned circuit provides a changing amplitude of response, converting FM to AM.
AM receivers may detect some FM transmissions by this means, although it does not provide an efficient means of detection for FM broadcasts. Applications[ edit ] Magnetic tape storage[ edit ] FM is also used at intermediate frequencies by analog VCR systems including VHS to record the luminance black and white portions of the video signal.
Commonly, the chrominance component is recorded as a conventional AM signal, using the higher-frequency FM signal as bias. But in Frequency Modulation FMthe frequency of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal. The amplitude and the phase of the carrier signal remains constant whereas the frequency of the carrier changes. This can be better understood by observing the following figures.
The frequency of the modulated wave remains constant as the carrier wave frequency when the message signal is at zero. The frequency increases when the message signal reaches its maximum amplitude. Which means, with the increase in amplitude of the modulating or message signal, the carrier frequency increases.
Principles of Communication Angle Modulation
Likewise, with the decrease in the amplitude of the modulating signal, the frequency also decreases. The deviation of the frequency of the carrier signal from high to low or low to high can be termed as the Carrier Swing. The modulation index is small. This is used in mobile communications such as police wireless, ambulances, taxicabs, etc.