Frequency modulation the amplitude

Frequency modulation the amplitudeINTRODUCTIONIn frequence modulation the amplitude is kept constant and the relative relative relative frequency is intoned by the amplitude of the modulating distinguish. The modulation index for fm is m = utmost frequency deviation/modulating frequency. FM signal can be equal as-v = ac take advantage(wct + m sin wmt )ABSTRACTFrequency modulation is a type of modulation where the frequency of the carrier is varied in accordance with the modulating signal. The amplitude of the carrier remains constant.The breeding-bearing signal (the modulating signal) departs the instantaneous frequency of the carrier. Since the amplitude is kept constant, FM modulation is a low-noise process and provides a in high spirits quality modulation technique which is employ for music and speech in hi-fidelity disseminates.In addition to hi-fidelity tuner transmission, FM techniques argon used for other of the essence(p) consumer applications such as sound sy nthesis and recording the luminance portion of a video signal with less distortion.There are several devices that are capable of generating FM signals, such as a VCO or a reactance modulator.Frequency Modulation is abbreviated FM.DefinitionsAn important concept in the understanding of FM is that of frequency deviation. The amount of frequency deviation a signal experiences is a measure of the change in leaveter output frequency from the rest frequency of the transmitter. The rest frequency of a transmitter is defined as the output frequency with no modulating signal applied. For a transmitterwith linear modulation characteristics, the frequency deviation of the carrier is instanter proportional to the amplitude of the applied modulating signal.Mathematical Analysis of FMAs was done with AM, a mathematical analysis of a high-frequency sin wave, modulated by a single tone or frequency, will be used to yield information about the frequency components in an FM wave, FM major power relations, and the bandwidth of an FM signal. From the definition of frequency deviation, an equation can be written for the signal frequency of an FM wave as a function of timefsignal = fC + kf eM(t) = fC + kf EM sin?MtAnd substitution of d = kf EM yieldsfsignal = fC + d sin?MtBut what does this equation foreshadow? It seems to be saying that the frequency of the transmitter is varying with time. This brings up the alike(p) type of problem that was observed when we looked at a time display of AM and then performed a mathematical analysis in an attempt to determineits frequency content. With AM, the signal appeared to be a sine wave thats amplitude was ever-changing with time. At the time, it was pointed out that a sine wave, by definition, has a constant peak amplitude, and thus cannot have a peak amplitude that varies with time. What about the sine waves frequency? It also must be a constant and cannot be varying with time.As was the case with AM, where it turned out that our m odulated wave was very the vector sum of three sine waves, a similar situation is true for FM. An FM wave will consist of three or a lot frequency components vectorially added together to give the appearance of a sine wave thats frequency is varying with time when displayed in the time domain. A somewhat compound mathematical analysis will yield an equation for the instantaneous voltage of an FM wave of the form shown hereeFM(t) = EC sin(?Ct + mf sin?Mt)where EC is the rest-frequency peak amplitude, ?C and ?M represent the rest and modulating frequencies, and mf is the index of modulation. This equation represents a single low-frequency sine wave, fM, frequency modulating another high-frequency sine wave, fC. Note that thisequation indicates that the argument of the sine wave is itself a sine wave.The Index of ModulationThe index of modulation, mf, is apt(p) by the following relationshipA few more comments about the index of modulation, mf, are appropriate. As can be seen from the equation, mf is equal to the peak deviation caused when the signal is modulated by the frequency of the modulating signal therefore, mf is a function of both the modulating signal amplitude and frequency. Furthermore, mf can take on any(prenominal) value from 0 to infinity. Its rangeis not limited as it is for AM.FM Power RelationsRecall that for an FM wave the amplitude of the signal, and hence the power, remains constant. This means that the power in the individual frequency components of the wave must add up to the transmitter output power. Furthermore, if the modulation index changes, the total power must distri scarcee itself over the resulting frequency components. If there is no modulation, then mf = 0 and J0 = 1.0. Mathematically, this can be shown by the followingPrest freq = J0 power 2 PtransorPrest freq = Ptransfor mf = 0.0.To determine the power for any individual frequency component, wecan use the following relationPn = Jn2(mf) Ptrans 4.11Furthermore, the total s ignal power will be given byPtotal = (J0power2 + 2J1power2 + 2J2power2 + 2J3power2 + ) Ptrans.The Effect of Noise on FMRecall AM and the effect of noise on it. Random electrical variations added to the AM signal alter the original modulation of the signal. For FM, noise still adds to the signal, but because the information resides in frequency changes instead of amplitude changes, the noise tends to have less of an effect. Expanding upon this idea a bit, one notes that the random electricalvariations encountered by the FM signal will indeed cause distortion by jittering the frequency of the FM signal. However, the change in frequency modulation caused by the jittering usually turns out to be less than the change in the amplitude modulation caused by the same relativeamplitude noise variations on an AM signal. Also unlike AM, the effect of the frequency jittering becomes progressively worse as the modulating frequency increases. In other words, the effect of noise increases with mo dulation frequency. Pre-Emphasis and De-EmphasisTo compensate for this last effect, FM communication systems have incorporated a noise-combating system of pre-emphasis and de-emphasisFM Generation TechniquesFM signals can be generated using either direct or indirect frequency modulation.Direct FM modulation can be achieved by directly feeding the message into the input of a VCO.For indirect FM modulation, the message signal is integrated to generate a phase modulated signal. This is used to modulate a crystal controlled oscillator, and the result is passed through a frequency multiplier to give an FM signalDIRECT FM GENERATIONThe simplest method for generating FM directly is to vary the frequency of an oscillator. A capacitance microphone or a varactor diode may be used as part of the oscillators frequency determining network. The capacitor microphones capacitance varies in response to the intensity of the sound waves striking it, making the oscillators frequency vary as the amplit ude of the sound varies. The varactor diodes capacitance depends on the voltage across it. Audio signals placed across the diode cause its capacitance to change, which in turn, causes the frequency of the oscillator to vary.INDIRECT FM GENERATION plot 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 radical of the Armstrong modulator.The mathematics required to analyze the Armstrong modulator completely are complex, so we will discuss save 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.. 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, date keeping the deviation constant so that additional multiplier stages can be used to obtain more deviation.FM Perfor military manceFM SpectrumA spectrum represents the relative amounts of different frequency components in any signal. Its like the display on the graphic-equalizer in your stereo which has leds showing the relative amounts of bass, midrange and treble. These correspond directly to increase frequencies (treble being the high frequency components). It is a well-know item of mathematics, that any function (signal) can be decomposed into purely sinusoidal components (with a few pathological exceptions) . In technical terms, the sines and cosines form a complete set of functions, also known as a basis in the infinite-dimensional vector space of real-valued functions (gag reflex). Given that any signal can be thought to be made up of sinusoidal signals, the spectrum then represents the recipe card of how to mak e the signal from sinusoids. Like 1 part of 50 Hz and 2 parts of 200 Hz. Pure sinusoids have the simplest spectrum of all, just one componentIn this example, the carrier has 8 Hz and so the spectrum has a single component with value 1.0 at 8 Hz . The FM spectrum is considerably more complicated. The spectrum of a simple FM signal looks likeThe carrier is now 65 Hz, the modulating signal is a pure 5 Hz tone, and the modulation index is 2. What we see are multiple side-bands (spikes at other than the carrier frequency) separated by the modulating frequency, 5 Hz.There are roughly 3 side-bands on either side of the carrier. The shape of the spectrum may be explained using a simple heterodyne argument when you mix the three frequencies (fc, fm and Df) together you get the sum and difference frequencies.The largest combination is fc + fm + Df, and the smallest is fc fm Df. Since Df = b fm, the frequency varies (b + 1) fm above and below the carrier. A more realistic example is to use a n audio spectrum to provide the modulationIn this example, the information signal varies amongst 1 and 11 Hz. The carrier is at 65 Hz and the modulation index is 2. The individual side-band spikes are replaced by a more-or-less invariable spectrum. However, the extent of the side-bands is limited (approximately) to (b + 1) fm above and below. Here, that would be 33 Hz above and below, making the bandwidth about 66 Hz. We see the side-bands extend from 35 to 90 Hz, so out observed bandwidth is 65 Hz.You may have wondered why we ignored the smooth humps at the extreme ends of the spectrum. The truth is that they are in fact a by-product of frequency modulation (there is no random noise in this example). However, they may be safely ignored because they are have only a minute fraction of the total power. In practice, the random noise would obscure them anyway.Frequency ResponseFrequency response is a specification used in amplifiers, pre-amplifiers, CD players, tape decks and other au dio components to measure how uniformly it reproduces sounds from the lowest tones to the highest. An amplifier or other component should preserve the loudness relationship between various instruments and voices and should not over or under-emphasize any frequency or tone. This is known as flat frequency response.BandwidthAs we have already shown, the bandwidth of a FM signal may be predicted usingBW = 2 (b + 1 ) fmwhere b is the modulation index and fm is the maximum modulating frequency used.FM radio has a significantly larger bandwidth than AM radio, but the FM radio band is also larger. The combination keeps the number of available take about the same.The bandwidth of an FM signal has a more complicated dependency than in the AM case (recall, the bandwidth of AM signals depend only on the maximum modulation frequency). In FM, both the modulation index and the modulating frequency affect the bandwidth. As the information is made stronger, the bandwidth also grows.Applications of frequency modulationBroadcastingFM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech . Normal (analog) TV sound is also broadcast using FM. A narrow band form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space.SoundFM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature for several generations of personal computer sound cards. radio setAn example of frequency modulation. This diagram shows the modulating, or message, signal, xm(t), superimposed on the carrier wave, xc(t)The modulated signal, y(t), produced from frequency-modulating xc(t) with xm(t).A Method of Reducing Disturbances in Radio Signaling by a Sy stem of Frequency Modulation called radio FM.As , wideband FM (W-FM) requires a wider signal bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against noise and interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission hence the term FM radio (although for many years the BBC called it VHF radio, because commercial FM broadcasting uses a well-known part of the VHF band in certain countries, expressions referencing the more known wavelength notion are still used in place of the more abstract modulation technique name).A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals). For a given signal strength (measured at the receiver antenna), switching amplifiers use less battery power and typically fol low less than a linear amplifier. This gives FM another advantage over other modulation schemes that require linear amplifiers, such as AM and QAM.REFRENCEShttp//en.wikipedia.org/wiki/Frequency_modulationhttp//www.tech-faq.com/frequency-modulation.shtmlhttp//www.fas.org/man/dod-101/navy/docs/es310/FM.htmhttp//www.answers.com/topic/frequency-modulation