FM tape recorder is also called FM recording system. In this, FM modulator, FM demodulator and low parse filter are used, with the help of which the recording of the signal is done. In this, the carrier signal frequency is modulated by the input signal, this process is known as FM modulation. In this recorder the input signal is recorded on tape as normal. In this, the center frequency is selected in relation to the tape speed. The frequency deviation for tape recorders is chosen around the carrier frequency. Hence the value of frequency deviation is 40%. Usually the reproduce head reads the tape and then transmits the signal to the FM demodulator and low pass filter. The reconstructed signal is received at the output of the low pass filter.
Frequency Modulation ( FM ) Recording in DC The output response to voltage is obtained more accurately. In this recording system the carrier oscillator frequency (fc) is modulated by the level of the input signal. In this, when the value of the input is zero, oscillations are also present in the modulation along with the center frequency. In FM recording, the application of a positive input voltage causes the carrier frequency to deviate in one direction by a specified percentage, and conversely, the application of a negative input voltage causes the carrier frequency to deflect in the opposite direction by an appropriate percentage of the modulation output to the tape. feed happens. tape signal dc The constant for the input is of frequency. AC There is a frequency change for the signal in which the change in frequency is directly proportional to the amplitude of the input signal. The output received from the frequency demodulator is fed into the low pass filter which removes the desired frequency and carrier generated in the modulation process. The operation of the FM modulator simply checks the known input voltage used and measures the output of the electronic counter. This signal is not used on tape under any circumstances And does not depend on the amplitude. In this, the residual carrier signal and any band noise can be easily removed through the low pass filter. FM recording shown in block diagram
The signal to noise ratio of an FM type tape recorder is of the order of 40.50 dB. The accuracy ° of this recorder is less than 1%. At 80 kHz frequency and 120 in/s tape speed, the FM recorder's +1 dB flat response becomes even higher when a very high carrier frequency is used in an FM type tape recorder. It uses +40% full scale frequency deviation. Mostly it is used for vibration measurement, in which a lot of data is recorded with the help of multi channels, the dynamic range of this recorder is 60 dB and the frequency range is from 0 to 10 kHz.
Advantages - The following are the advantages of FM recording
(i) This recording is free from dropout effect.
(ii) This recording is useful for multiplexing in instrumentation systems.
(iii) This recording system has a much wider frequency range and records frequencies of the order of kilo Hz.
(iv) It is independent of amplitude change.
(v) It accurately reproduces the waveform of the input signal.
(vi) This recording also records quantities such as force, pressure and acceleration in the form of voltage.
Disadvantages - The following are the disadvantages of FM recording
(i) FM recording is more sensitive to fluctuations in tape speed.
(ii) FM circuitry is more complex than that of a direct recording system.
iii) These recording systems are limited by the high frequency response of 80 kHz.
(iv) It requires high tape speed. (v) It requires high quality tape transport.
(vi) It is more expensive than the direct recording system.
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