Segment of helical scan video tape as it is being erased
For recording the audio, the bias signal is used for the same purpose as in a
standard audio recorder.
a. The bias signal provides bias power for the control track head; it is
modulated by the vertical sync and recorded as control track pulses.
b. In the video record mode, the bias signal provides a carrier signal for
recording the video.
This is made possible (even though the video frequencies
cover a much wider range than audio) by the use of video signals to control the
frequency of an FM modulator.
c. The resulting FM signal is applied to the bias oscillator frequency, which
establishes the voltage level, for FM recording of the video on the magnetic tape.
Servo frequencies are a combination of several other frequency inputs.
servo frequencies can be best described by indicating their various inputs sources.
a. The tachometer, plus the tachometer pickup, generates a frequency input to
the servo. The tachometer frequency will vary among manufacturers and even among
recorders in a model series.