Method for recording information signal and control signal

A first main information signal is recorded in a first track extending longitudinally along one side of a length of magnetic tape and a corresponding first secondary, or control, signal is recorded in a narrow parallel track spaced from the first main track. A second main signal is recorded in a third track within the other half of the tape, and a corresponding second secondary, or control, signal is recorded between the first secondary signal and the first main signal, whereby the two main signals and the two secondary signals are interleaved with each other. The first and second main tracks are equal in width, and the first and second secondary tracks are also equal in width but are much narrower than the first and second main tracks. If desired, the first and second main tracks can each be divided into first and second sub-main tracks to permit two channel recording with a control track in each direction but with each control, or secondary, track being separated from its own nearest subtrack by a distance equal to the width of the other secondary track plus two guardbands, one on each side of the other secondary track.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and apparatus for recording information 
signals and related secondary signals in parallel tracks on a magnetic 
recording medium. In particular, it relates to a method and apparatus for 
recording one set of main and secondary signals on a first main and a 
first secondary track parallel to each other and spaced apart from each 
other and interleaved with a second main and a second secondary track on 
which a second information signal and a second related signal is recorded, 
respectively. The secondary track related to a second main track is 
recorded between the first main track and the first secondary track 
related thereto, so that both secondary tracks are between their related 
main tracks. 
2. The Prior Art 
In certain types of magnetic tape equipment, a main signal is recorded 
simultaneously with a secondary signal. The secondary signal is frequently 
referred to as a control signal and contains control information, such as 
pulses corresponding to blocks of information in the information signals 
to allow a counting mechanism to count the number of such pulses in order 
to move the tape to desired locations thereon to pick up information 
recorded at such locations. Due to the fact that the secondary signals 
contain relatively little information, they do not require as much tape 
width as the main signals recorded simultaneously. 
In some conventional tape recorders the control signals are recorded in 
very narrow tracks at the edges of the tape. Each main signal and the 
control, or secondary, signal associated therewith are recorded on 
slightly less than one half the total tape width with the tape moving in 
one direction. The other half of the tape has another main signal and 
another control signal recorded on it with the tape moving in the opposite 
direction. The arrangement of recording tracks in which the signals are 
recorded is symmetrical about the center line of the tape. As a result, if 
the moving tape fluctuates a small amount in the transverse direction 
while it is being pulled in the longitudinal direction, the pick up head 
that should respond to the narrow track of the recorded control signals 
may be shifted away from that track, thus making the control track 
operation unstable. To make matters worse, the head may disengage entirely 
from the track. This causes some of the signals to be dropped out, and in 
the case of control signals that are to be counted, this has an 
unacceptable influence on the count. 
It has been proposed, in order to overcome the disadvantage of losing 
contact with the control tracks, to place the control tracks near the 
center of the tape. As before, one-half of the tape is used to record one 
main intelligence signal and its corresponding secondary, or control, 
signal while the tape moves in one direction and the other half is used to 
record a second main intelligence signal and its related secondary signal 
when the tape is moved in the other direction. The two control signals are 
recorded adjacent each other and the main signals are recorded in broader 
tracks near the outer edges of the tape. However, this still produces 
cross-talk between each of the main information signals and the respective 
secondary signals because each pair of main and secondary signals is 
spaced only a very short distance apart. In addition, the magnetic head to 
accomplish such spacing is difficult to construct because the part that 
records the second signal must be relatively close to the part that 
records the main signal. 
OBJECTS AND SUMMARY OF THE INVENTION 
The principle object of this invention is to overcome the problems still 
found in recording both the main information signal and the corresponding 
secondary signal on tracks on one side of the center line of the magnetic 
tape and recording the second main signal and the corresponding secondary 
signal on tracks on the other side of the center line of the magnetic 
tape. 
In accordance with this invention the recording is carried out so that 
there is enough space between the first main track on which the first main 
information signal was recorded and the corresponding secondary track to 
allow the second secondary track to be placed in that space with 
relatively narrow guard bands between the second secondary track and the 
first main track and between the second secondary track and the first 
secondary track. In addition, the second main track is separated from its 
secondary track by the first secondary track. The resultant tracks form an 
interleaved pattern consisting of a first main track, a second secondary 
track, a first secondary track and a second main signal. Typically, the 
first main track and the first secondary track are recorded with the tape 
moving in one direction and the second main track and its second secondary 
track are recorded with the tape moving in the opposite direction. This, 
in itself, reduces cross-talk between the two main tracks and the nearest 
secondary track.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows one pattern of recordings carried out by prior art tape 
recorders. In FIG. 1 the tape is indicated by reference numeral 1 and has 
recorded thereon a first main track 2 containing an information signal. 
This track is recorded in what may conventionally be called the forward 
direction as shown by the arrow A. The tape also includes another main 
track 3 substantially identical with track 2 but recorded with the tape 
moving in the reverse direction as indicated by the arrow B. A much 
narrower secondary track 4 is recorded alongside the main track 2 and 
between the track 2 and the closest edge of the tape 1. A second secondary 
track 5 corresponding to the second main track 3 is recorded between that 
main track and the closest edge of the tape 1. The tracks 2 and 4 are 
recorded simultaneously as are the tracks 3 and 5. One use for such 
secondary tracks is to record control signals to control the operation of 
playback mechanisms. The track 4 may have recorded on it control signals 
to control the operation when the tape 1 is moving in the forward 
direction. The track 5 may have control signals recorded on it to control 
the operation of the playback mechanism when the tape 1 is moving in the 
reverse direction to play back the second main, or information, signal 3. 
The width of the tape 1 is typically 1/4 inch, or about 6.3mm, and the 
width of the secondary tracks 4 and 5 are each about 0.2mm. Thus, if the 
tape moves transversely or vibrates when it is in motion in either 
direction the contact of the playback head that is to engage the secondary 
track is likely to be unstable, thereby causing drop outs of the signals 
played back from the secondary tracks. Such signals are likely to be 
control signals and thus to result in erratic and undesirable control 
operation. 
It has previously been proposed to overcome this difficulty by recording 
the secondary tracks between the main tracks as shown in FIG. 2. The tape 
in FIG. 2 is indicated by reference numeral 11 and is provided with main 
tracks 12 and 13 corresponding to tracks 2 and 3 in FIG. 1. Track 12 is 
recorded with the tape moving in the forward direction as indicated by the 
arrow A and track 13 is recorded with the tape moving in the reverse 
direction indicated by the arrow B. A secondary, or control, signal 
related to the information in track 12 is recorded in a very narrow track 
14 directly alongside the track 12 and between the two main tracks 12 and 
13. Similarly, a secondary, or control, signal related to the information 
in track 13 is recorded in a very narrow track 15 directly alongside the 
track 13 and between the latter and track 14. 
FIG. 2 shows accepted track dimensions and spacings for recording tape 
having an overall width D of 6.3mm(1/4 inch). The width d.sub.1 between 
the nearest edges of the tracks 12 and 13 is 1.05mm., and the width 
d.sub.2 of each of the main tracks 12 and 13 is 2.55mm. The width d.sub.3 
of each secondary track is 0.2mm. The spacing d.sub.4 between the tracks 
14 and 15 is also 0.2mm., and the spacing d.sub.5 between each control 
track 14 or 15 and its respective main track 12 or 13 is 0.225mm. 
Generally, a combination recording and playback transducer is used for 
recording or reproducing both an information signal and its associated 
secondary signal simultaneously. However, if the information track and the 
associated secondary track are formed close to each other, as described 
above, the information head core and the secondary head core that form 
these tracks must be located very close to each other. This makes it 
possible for magnetic coupling between the head cores to cause an 
undesirable amount of crosstalk, which causes deterioration in the quality 
of the reproduced information signal. 
One embodiment of the present invention will be described with reference to 
FIG. 3. The fundamental difference between the arrangement of tracks in 
FIGS. 2 and 3 is that the location of the secondary tracks are reversed. 
In FIG. 3 the secondary track 14 associated with the main information 
track 12 is not adjacent track 12 but is separated from it by the 
secondary track 15. Correspondingly, the track 14 is located between the 
other secondary track 15 and the main information track 13 associated with 
the track 15. The relationship between the main and secondary tracks is 
clarified by the arrows A, which indicate that the tracks 12 and 14 are 
recorded when the tape 11 is moving in the forward direction and the 
arrows B that indicate that the tracks 13 and 15 are recorded when the 
tape is moving in the reverse direction. 
There still remains a guardband between each pair of tracks. However, the 
guardband between the secondary tracks 14 and 15 can be even narrower than 
the guardbands between the tracks 12 and 15 and between the tracks 13 and 
14. 
FIG. 4 shows the face of a combination magnetic head 16 to record or 
reproduce information according to the track format shown in FIG. 3. The 
head 16 has a relatively wide pair of pole pieces 17 and 18 that meet at 
an air gap 19. The length of the air gap is equal to the width of the 
track 12 in FIG. 3 and the width of the air gap is infinitesimal. Spaced 
from the pole pieces 17 and 18 are two much narrower pole pieces 20 and 21 
that define another air gap 22 between them and directly aligned with the 
air gap 19. The spacing between the closest edges of the upper pole pieces 
17 and 18 and the lower pole pieces 20 and 21 is d.sub.7 which is 
approximately equal to the sum of distances d.sub.3 + d.sub.4 + d.sub.5 in 
FIG. 2, or approximately 0.625 mm. The relatively large spacing between 
the upper and lower pole pieces makes it easier to construct the magnetic 
head 16 than if this spacing were only 0.2mm. as it had to be in the case 
of the prior art arrangement to record the main track 12 and the 
corresponding secondary track 14 very close to each other as was done in 
FIG. 2. Additionally, the wide spacing d.sub.7 greatly reduces the 
crosstalk between the upper poles 17 and 18 and the lower poles 20 and 21. 
FIG. 5A shows another tape format similar to that in FIG. 3 except that the 
first main information track 12 has been divided into two subtracks 12a 
and 12b, each of which can carry information. In a similar manner the 
other main information track 13 has been divided into two subtracks 13a 
and 13b. Both of the subtracks 12a and 12b and the secondary track 14 
associated with them are recorded when the tape 11 is traveling in the 
forward direction as shown by the arrows A. The other two subtracks 13a 
and 13b and the secondary track recorded along with them are recorded when 
the tape 11 is moving in the reverse direction indicated by the arrows B. 
Each of the subtracks 12a, 12b, 13a and 13b has a width of approximately 
1.1mm. Each pair of subtracks, for example the pair 12a and 12b, has a 
guardband d.sub.9 of approximately 0.35mm between them. The tracks 13a and 
13b have this same guardband d.sub.9 of about 0.35mm between them also. It 
will be noticed that the guardband width of 0.35mm is slightly larger than 
the guardband widths d.sub.5 or d.sub.6, each of which is 0.225mm or 
d.sub.4 which is 0.2mm. 
In order to record the track format illustrated in FIG. 5A a combination 
magnetic head is used. This head includes two pole pieces 24 and 25 with 
an airgap 26 between them to record the subtrack 12a when the tape 11 is 
moving in one direction and the track 13a when the tape 11 is reversed and 
moved in the opposite direction. The head includes a second set of pole 
pieces 27 and 28 defining a second airgap 29 exactly aligned with the 
airgap 26 to record the subtrack 12b and, in the reverse direction, the 
subtrack 13b. The secondary track 14 related to the subtracks 12a and 12b 
is recorded by a third pair of pole pieces 30 and 31 defining a third gap 
32 therebetween. This gap is directly aligned with the airgaps 26 and 29. 
The same pole pieces may be used to playback the tracks previously 
recorded by the head 23 or an identical head. The pole pieces 30 and 31 
are still spaced by the distance d.sub.7 from the closest side of the 
closest pair of pole pieces 27 and 38 to make it as easy as possible to 
construct the head and to make it possible to reduce cross-talk between 
the nearest set of pole pieces 27 and 28 and the pole pieces 30 and 31 
that record or playback the secondary track that corresponds to the main 
information signals recorded on the subtrack 12b. 
FIG. 5C shows an erasing head 33 having only two main pole pieces 34 and 35 
defining an airgap 36 therebetween and having an overall airgap length 
equal to the width of the subtracks 12a and 12b and the guardband between 
them. The erase head 33 also includes another pair of pole pieces 37 and 
38 with an airgap 39 between them to erase the secondary track that 
corresponds to the main information track or subtracks being erased by the 
flux between the pole pieces 34 and 35. The pole pieces 37 and 38 must be 
spaced from the closest edge of the erasing pole pieces 34 and 35 by the 
same distance d.sub.7 referred to previously. 
This invention has been described in terms of specific embodiments although 
it will be understood by those skilled in the art that other embodiments 
may be used instead, and that the true scope of the invention is defined 
by the following claims.