Analog Communication Systems (4th Edition), Oxford University Press. 1 Basic Figure 1: An illustration of phase-modulated and frequency-modulated signals. Angle modulation schemes has a nonlinear relationship between s(t) and m(t). Know the relationship of carrier frequency, modulation frequency and modulation FM systems to AM systems with regard to efficiency, bandwidth and noise. vary one of the three parameters of the signal: amplitude, frequency or phase. modulation is achieved at the expense of increased system .. Figure Illustrating the relationship between frequency modulation and phase modulation .
For indirect FM modulation, the message signal is integrated to generate a phase-modulated signal. This is used to modulate a crystal-controlled oscillatorand the result is passed through a frequency multiplier to produce an FM signal.
Principles of Communication Angle Modulation
In this modulation, narrowband FM is generated leading to wideband FM later and hence the modulation is known as indirect FM modulation. Detectors Many FM detector circuits exist. 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. Slope detection demodulates an FM signal by using a tuned circuit which has its resonant frequency slightly offset from the carrier.Phase Modulation (Basics, Definition and Waveform) [HD]
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. Phase Modulation is the process of varying the phase of the carrier signal linearly with the message signal.
Let us now discuss these topics in greater detail. Frequency Modulation In amplitude modulation, the amplitude of the carrier varies. But in Frequency Modulation FMthe frequency of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal.
- Frequency modulation
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.
Frequency modulation - Wikipedia
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. The modulation index is large, i. Its spectrum consists of a carrier and infinite number of sidebands, which are located around it.