modulation in phase and frequency - Electrical Engineering Stack Exchange
AM-amplitude modulation FM-frequency modulation PM-phase modulation In Phase Modulation, modulation index is directly proportional to. Difference: * In PM, phase of carrier signal changes while in FM frequency of carrier signal changes in accordance with the instantaneous value of modulating . namely amplitude modulation (AM) and frequency modulation (FM) cues, known to be . The relationship between attenuation and SNR was a broken stick function. .. Biometrika (Biometrika Trust) ;10(4)–
Amplitude of the modulated carrier remains constant in both modulation systems. BDG xx 3 An important feature of angle modulation: It can provide a better discrimination robustness against noise and interference than AM. In FM, the frequency of carrier is varied directly.
In PM, phase of the carrier is varied directly. The instantaneous frequency deviation is the instantaneous change in carrier frequency and is equal to the rate at which instantaneous phase deviation takes place.
For PM, the maximum frequency deviation takes place near zero crossing of the modulating signal. It is diffcult to know from modulated waveform whether the modulation is FM or PM. The low index systems are called narrowband FM in which frequency spectrum resembles AM. The power of an unmodulated carrier is redistributed in the carrier and sidebands after modulation. The average power of angle modulating signal, MI and FD.
Spectrum contains infinite numbers of sidebands and carrier as against two sidebands and carrier in NBFM. Used for broadcast and entertainment as against for mobile communication for NBFM. As the amplitude of FM carrier is constant, the noise interference is minimum. The amplitude of FM carrier is constant and is independent of depth of modulation. Hence transmitter power remains constant in FM whereas it varies in AM.
As against the limitation of depth of modulation in AM, in FM depth of modulation can be increased to any value, without causing any distortion. BDG xx 21 4. Because of guard bands provided in FM, adjacent channel interference is very less.
Principles of Communication Angle Modulation
Radius of propagation is limited as FM uses space waves with line of sight. So it is possible to operate many independent transmitters on the same frequency with minimum interference. FM equipments are more complex and hence costly.
Area covered by FM is limited, to line of sight area but AM coverage area is large. FM radio was developed in the United states mainly by Edwin Armstrong in the s.
Modulating differences In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted. Importance It is used in both analog and digital communication and telemetry It is used in both analog and digital communication and telemetry Frequency Range AM radio ranges from to KHz OR Up to Bits per second.
FM radio ranges in a higher spectrum from 88 to MHz. OR to bits per second. In AM radio broadcasting, the modulating signal has bandwidth of 15kHz, and hence the bandwidth of an amplitude-modulated signal is 30kHz.
Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth required is kHz.
- Difference between AM and FM
- FREQUENCY AND PHASE MODULATION (ANGLE MODULATION)
Transmitter and receiver are more complex as variation of modulating signal has to be converted and detected from corresponding variation in frequencies. Noise AM is more susceptible to noise because noise affects amplitude, which is where information is "stored" in an AM signal.
FM is less susceptible to noise because information in an FM signal is transmitted through varying the frequency, and not the amplitude. FM PM 1 The max frequency deviation depends on amplitude of modulating signal and its frequency The max phase deviation depends on amplitude of modulating signal 2 Frequency of the carrier is modulated by modulating signal. Phase of the carrier is modulated by modulating signal.
Modulation index remains same if modulating signal frequency is change.
Modulators — Carrier frequency can be generated by LC oscillator. By varying the values of L or C of tank circuit, carrier frequency can be changed. When these components are used with LC tank circuits, we are able to vary frequency of oscillator by changing the reactance of L or C.
Indirect FM — Modulation is obtained by phase modulation of the carrier An instantaneous phase of the carrier is directly proportional to the amplitude of the modulating signal.
Direct FM- The frequency of carrier is varied directly by modulating signal An instantaneous frequency variation is directly proportional to the amplitude of the modulating signal.
Frequency modulation using Varactor Diode — There exists small junction capacitance in the reverse biased condition of all the diodes. The varactor diodes are designed to optimise this characteristic. As the reverse bias across varactor diode is varied, its junction capacitance changes.
These changes are linear and wide 1 to pF BDG xx 30 Frequency modulation using varactor diode — All diodes show small junction capacitance in the reverse biased condition.
High frequency stability as crystal oscillator is isolated from modulator. To avoid distortion, the amplitude of modulating signal is to be kept small. Depending on several factors such as range, application and budget, modulation can be casted into three types: Out of these three types, the former two are widely known as they form a major commercially applicative part of radio communication.
In this article, we will discuss common difference between AM and FM which will enhance our learning in terms of these two technologies. Formulated in the s, AM is a relatively older modulation process compared to FM which was found in the s by Edwin Armstrong.
AM stands for amplitude modulation where the amplitude of the carrier is modulated as per the message signal. The other aspects of the carrier wave such as frequency phase etc.
On the other hand, FM means frequency modulation and in it only frequency of the carrier wave changes while amplitude, phase etc. Frequency range of working: FM based signal transmission consumes a higher amount of power than an equivalent AM based signal transmission system. Signal quality is a lot superior in FM than AM as amplitude based signals are more susceptible to noise than those which use frequency.
Moreover, noise signals are difficult to filter out in AM reception whereas FM receivers easily filter out noise using the capture effect and pre-emphasis, de-emphasis effects. In capture effect, the receiver locks itself to catch stronger signal so that signals received are more synced with that at the transmitting end. In pre-emphasis, de-emphasis process, the signal is further amplified to a higher frequency at sending end pre-emphasis and vice versa at receiver end de-emphasis.
These two processes reduce down the chances of a signal to get mixed with other signals and make FM more immune to noise than AM. Fading refers to power variation during signal transmission.