or narration. Guard bands are provided between the tracks to prevent cross-talk. The two audio tracks
are sometimes used for stereo recordings and in many cases today the second track is used to record, in a
different language, the same information that is recorded on the first track. This type of recording is
used more today because of the bilingual method of instruction.
The video track, as the name implies, is used for recording all video information. These tracks
are recorded at an angle between 30 degrees and 90 degrees. The exact angle will depend on the
manufacturer and the design of the recorder.
There are 262 1/2 lines of picture information in one television field. Two fields equal one frame
and one frame is equal to one television picture. The quadruplex recorder requires 16 transverse tracks
to record one field or 32 transverse to record one frame, which is one complete television picture. The
helical recorder uses one diagonal track to record one field or two tracks to record a complete picture.
Where the quadruplex recorder uses a track of less than 2 inches in length, the helical recorder uses a
track which may be up to 10 inches long. With the helical putting the entire television frame on two
diagonal lines, you can see how even a slight misalignment or improper spacing of tracks at the various
points of the tape could cause a pronounced effect on the picture when it is displayed on a monitor.
The signal recorded on the control track is normally a 30 Hz signal; however, on some early
machines, this signal was recorded at 60 Hz. This signal, when used in comparison with a signal from
the head drum, is used to control the speed of the head drum assembly during the playback mode.
Magnetic tape is a strong permanent recording medium and is unaffected by normal handling.
Avoid contact with the oxide surface of the tape since fingerprints may cause dust buildup and the
possible loss of signal (dropout). When not in use, video tape should be stored away from stray
magnetic fields and under temperature and humidity conditions recommended by the manufacturer.
Helical scan recorders are used in many areas in the civilian community as well as the military.
They are used in the medical field, education, security and surveillance, industrial monitoring, as well as