Analogue optical link for multichannel frequency-modulated television transmission
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Abstract:
The performance of an analogue optical link for the transmission of multichannel frequency-modulated TV signals with small frequency deviations is measured. A signal/noise ratio of 47 dB is achieved on a four-channel PAL system with a frequency deviation of 600 kHz, a bandwidth of 16 MHz per channel and an interchannel spacing of 18 MHz.Keywords:
Frequency deviation
Optical link
Channel spacing
Link (geometry)
The performance of an analogue optical link for the transmission of multichannel frequency-modulated TV signals with small frequency deviations is measured. A signal/noise ratio of 47 dB is achieved on a four-channel PAL system with a frequency deviation of 600 kHz, a bandwidth of 16 MHz per channel and an interchannel spacing of 18 MHz.
Frequency deviation
Optical link
Channel spacing
Link (geometry)
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Equations are derived for the carrier and side-frequency amplitudes which are obtained when a carrier wave is frequency-modulated by a complex audio signal. The bandwidth occupied by such a frequency-modulated wave is defined as the distance between the two frequencies beyond which none of the side frequencies is greater than 1 per cent of the carrier amplitude obtained when the modulation is removed. Curves are given to show the amount this bandwidth exceeds the extremes of deviation for a range of modulation indexes from 0.1 to 10,000, for sinusoidal, square, rectangular, and triangular modulation. For more precise definitions of bandwidth, curves are also given for side-frequency amplitude limits of 0.1 per cent and 0.01 per cent of the carrier-wave amplitude. For complex modulatlon the total bandwidth can be estimated by computing the bandwidth that would be required by each audio-frequency component, if it were on separately, and adding the results.
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Modulation (music)
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This paper presents a new digital frequency modulation scheme using digital sinusoidal oscillator, By multiplying an information signal with the oscillator coefficient, positions of the system poles are varied according to the strength of the incoming signals. As a result, the frequency modulation is obtained. The advantage of this system is that its frequency deviation and bandwidth are directly defined by the initial frequency condition of the system and are independent of the signal strength. Thus, the signal bandwidth is easily controlled. Computer simulation results are provided to confirm that the proposed system is the frequency modulator.
Frequency deviation
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Pulse-frequency modulation
Pulse-density modulation
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An examination of the frequency distribution of the power in typical broadcast signals shows that low-deviation phase modulation (PM) should have advantages over amplitude (AM) and frequency modulation (FM). A method of stereo broadcasting is also proposed in which the sum of the two channels is transmitted as AM and the difference as PM.
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Frequency deviation
Phase difference
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The presented paper deals with determination of the critical modulation frequency (CMF) and critical bandwidth in the case of random amplitude and frequency changes in a sinusoidal signal. The critical modulation frequency is the smallest value of modulation frequency for which thresholds for detecting amplitude and frequency modulation, expressed in appropriate modulation indexes (i.e. m and β), reach the same values. Random amplitude and frequency changes of the simple tone were produced in the amplitude and frequency modulation process by random modulating signals. The results of the investigations enable to state that the critical modulation frequency is an increasing function of the carrier frequency. It was also shown that psychoacoustically measurable quantities such as detection thresholds, the critical modulation frequency and quantities connected with it (i.e. critical bandwidth, a range of occurrence of a monaural phase effect}, do not depend on a modulating signal character (i.e. whether this signal is periodic or random}.
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Pulse-frequency modulation
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Frequency modulation is likely to play an important part in postwar radio developments. The present position of this method of communication is here reviewed; a brief discussion of the features of the three methods of modulation—amplitude, frequency and phase—is followed by a survey of the history of frequency modulation, with a consideration of its limitations, advantages and present applications.The first of the two main Sections of the paper is concerned with the production of a frequency-modulated signal; direct and indirect (integrated phase-modulation) methods are examined with particular reference to the variable-reactance valve modulator with automatic mean-frequency correction, and the indirect transposed-sideband modulator with a crystal-controlled master oscillator. Measuring and monitoring equipment is also described.The second main Section deals with frequency-modulated reception, and indicates the essential features of a frequency-modulated receiver, which, except for the amplitude limiter and frequency-to-amplitude converter (examined in detail), is similar to its ultra-short-wave counterpart for amplitude modulation. Also included are three Subsections dealing with tuning indicators, frequency-deviation compression, and distortion and interference. Possible future developments are discussed, and the paper concludes with a bibliography of the most important contributions to the literature of frequency modulation made over the past twenty years.
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Pulse-frequency modulation
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A method measuring the modulation indexes of square wave frequency modulation (SWFM) signals have been proposed and experimentally verified. The measurement circuit consists of a series of bandpass filters, DC rectifiers, analog-to-digital converters, and a processor for calculating the frequency deviation. In accordance with the modulation index of the SWFM signal at the fundamental and third-harmonic frequency of the IF carrier, the frequency deviation of the SWFM signal has been found to be precisely determined when the modulation signal is input to the SWFM signal modulator. This method is useful for determining suitable modulation signal levels for sideband spreading in the SWFM signal, and can be applied to the measurement of the modulation index at the transmitter in FM voice communication systems.< >
Frequency deviation
Modulation index
Modulation (music)
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Pulse-frequency modulation
Pulse-density modulation
Delta modulation
Square wave
Frequency multiplier
Radio transmitter design
Delta-sigma modulation
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Two-point frequency modulation gives a flat frequency response irrespective of the loop cutoff frequency of a p.l.l. digital frequency synthesiser. The spurious modulation components otherwise generated are also then suppressed. The modulation index is typically limited to Nπ where N is the divider ratio.
Wideband
Modulation (music)
Modulation index
Frequency deviation
Spurious relationship
Frequency multiplier
Pulse-frequency modulation
Cutoff frequency
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Estimation of the parameters of frequency-modulated (FM) signals presents a significant challenge when the peak frequency deviation is large in comparison with the modulation frequency. In the frequency domain, such signals contain many significant side-bands and so are considered to be wide-band FM signals. Standards are being developed for the testing of frequency and rate of change of frequency (ROCOF) measuring instruments used in electrical power transmission and distribution systems. To verify the measuring and operating ranges of these instruments under dynamic conditions, injection of wide-band FM signals with carrier frequency equal to the power system nominal frequency (50 Hz or 60 Hz) is being envisaged. A refinement is proposed here to one method of FM signal parameter estimation in the time domain which uses prior knowledge about the modulation frequency. This refinement overcomes convergence difficulties when the FM signal is wide-band by finding an improved initial estimate for the modulation phase.
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Frequency band
Pulse-frequency modulation
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Capture effect
Frequency deviation
Modulation (music)
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Carrier recovery
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