FM: Frequency Modulated Waves

Replies

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  durga ch

  Do you mean something like recording Live tv?
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  sauravgoswami

  FM record electronics use the input signal to vary (modulate) the carrier frequency of a record oscillator. The frequency modulated output signal of the record oscillator then becomes the signal that's actually recorded onto the magnetic media. Figure 5-4 shows a block diagram of the FM record electronics.
  Figure - FM record electronics.
  

  
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  FM record electronics consist of three main parts:
  Input pre-amplifier circuit.
  This circuit does two things: (a) it serves as an impedance matcher between the signal source and the magnetic recorder, and (b) it pre-amplifies the input signal.
  Record oscillator circuit.
  This circuit generates a carrier signal onto which the input signal will be modulated. The input signal is used to vary (frequency modulate) the carrier signal. This is how the input signal gets frequency modulated onto the carrier signal. The output of this circuit is the frequency-modulated carrier signal.
  The center frequency of the carrier depends on two things: (a) the bandwidth of the signal you're recording, and (b) the media onto which you're recording.
  For magnetic tape, the carrier frequency can be as low as 1.688 kHz for an operating tape speed of 1-7/8 inches per second, and as high as 900 kHz for 120 inches per second.
  Head driver circuit. This circuit takes the frequency-modulated output from the record oscillator circuit, amplifies it, and sends it to the magnetic head for recording. The output level of this circuit is set to be just below the magnetic saturation point of the magnetic media.
  FM REPRODUCE ELECTRONICS
  The FM reproduce electronics work just like direct reproduce electronics, with one exception. FM reproduce electronics must first demodulate the original input signal from the carrier frequency before the intelligence can be sent to the output device for listening or analysis. Figure 5-5 shows a block diagram of the FM reproduce electronics.
  Figure 5-5. - FM reproduce electronics.
  

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  FM reproduce electronics consist of four main parts:
  Pre-amplifier circuit.
  This circuit takes the frequency modulated carrier frequency from the reproduce head and amplifies it.
  Limiter/demodulator circuit.
  This circuit takes the output of the preamplifier, stabilizes the amplitude level, and demodulates the signal intelligence from the carrier frequency.
  Low-pass filter circuit.
  This circuit takes the signal intelligence from the limiter/demodulator circuit and cleans up any noise or left over carrier signal.
  Output amplifier circuit.
  This circuit takes the output from the low-pass filter and amplifies it for output. It also matches the impedance of the magnetic recorder to the output device.
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  integratdbrains

  Won't a Band Pass filter be required before the preamplifier circuit for the record circuit? I feel it will be required. What say Saurav?
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  sauravgoswami

  definately it will be required if you are recording it from a mobile or hand-held device!!! and we can also set the band-pass filter accordingly,a single DSP engine is enough to achive it!!!
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  just2rock

  yes it can be simply done using preequilizer & post equilizer circuit