Learning Event 2:
DESCRIBE THE PURPOSE AND USE OF THE DUAL HEAD RECORDERS
Dual head recorders use two rotating heads spaced 180 degrees apart, each
sweeping the same arc, respectively. In this case, the tape need not be wrapped in
a complete loop around the head drum assembly.
It should be noted that one head
will be in contact with the tape at all times. The heads are electrically switched
so that the head that is in contact with the tape at all times.
The heads are
electrically switched so that the head that is in contact with the tape is
continuously active during its pass. The long single dropout that was present in
the previous example is eliminated. Head switching may also occur during vertical
blanking when it will not be visible. This type of scanning is referred to as the
half-helical or two-head helix method of video recordings.
When two heads are used, extreme care must be taken to place the heads
accurately with respect to each other.
Mechanical tolerances are critical and
placement errors are easily introduced.
When the heads are not exactly 180 degrees apart, the error induced is called
dihedral error. If this error is large, it makes tape interchange between machines