Frequency modulation (FM) and Phase modulation. (PM) have much in FM. Where k f and k p represent the deviation constants of PM and FM respectively. Know the relationship of carrier frequency, modulation frequency and modulation index vary one of the three parameters of the signal: amplitude, frequency or phase. We have also introduced a new term: Df, the peak frequency deviation. Frequency (Fm) and Phase (Pm) Modulations - Free download as PDF File .pdf), Text File .txt) A close relationship exists between the PM and FM signals: Deﬁnition of frequency deviation and modulation index Let m(t) = Am cos(2πfmt) .
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.
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.
Frequency modulation - Wikipedia
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. 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. 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. 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.frequency modulation
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. This is used in entertainment broadcasting applications such as FM radio, TV, etc.
Phase Modulation In frequency modulation, the frequency of the carrier varies.