FM MODULATION
The techniques involved to record and replay video signals are not so straight forward as for audio signals. The main problem is the relatively large bandwidth of the video signals which for a broadcast-standard signal extends from dc (about 25 Hz in practice) to 5.5 MHz. For domestic video recorders a more limited response is adequate, the HF roll-off occurs at about 2.5 MHz, permitting more in sparing use of the tape.
A magnetic tape system's output level is proportional to the rate of change of the magnetic flux, so that output is directly geared to frequency. Thus each halving of frequency (octave) halves the output signal, giving the tape/head interface a characteristic 6 dB/octave curve, Fig. 33.3. Because the difference ...
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