Image:Magnetic recording diagram Us004390906-002.png

From U.S. Patent 4,390,906

FIG. 1 is a schematic top view of a first embodiment of the present invention;

FIG. 2 is a scanning portion on magnetic tape obtained by the first embodiment;

In FIG. 1 is shown a two-head helical-scanning type video tape recorder incorporating the present invention. Reference numeral 1 designates a supply reel and 2, a take-up reel. A magnetic tape 10 is transported in the direction indicated by an arrow 11 by a capstan 8 and a pinch roller 7 while wrapping around a cylinder 3. Posts 4, 5 and 9 are provided so as to ensure the smooth transport of the tape. A head 6 records and reproduces not only the audio signal but also the control signal.

The magnetic tape 10 is wrapped around the rotating head cylinder about 180.degree. (180.degree.+.alpha.+.theta..sub.1 +.theta..sub.2) and rotating heads H.sub.A and H.sub.B record the video signal in a series of oblique tracks as shown in FIG. 2.

Next, referring to FIG. 2, the scanning pattern on the magnetic tape 10 will be described in detail below. It is assumed that the cylinder head is rotating in the direction indicated by an arrow 12 and the tape is transported in the same direction as indicated by an arrow 11. FIG. 2 shows the scanning pattern as viewed from the front as with FIG. 1, but when viewed from the magnetic coating on the tape, the pattern must be viewed from the back of the paper.

In FIG. 2, A denotes the width of the tape; B, the whole width of the video signal recording band including overlaps; W, the contact width with which the 180.degree. video head makes a contact with the tape; C, the width of the audio track; F, the width of the guard track between the video signal recording band and the audio track; G, the width of the guard band between the video signal recording band and the control track; D, the width of the control track; M, the front overlapping width; N, the back overlapping width; CA, the width of the first channel track; CG, the width of the guard band between the first and second channels; and CB, the width of the second channel.

Next, the method for recording the audio signal in the audio track with a stationary head or a rotating head will be described. The width A of the tape is, for instance, 1/2 inch (equal to 12.65 mm) and the width D of the control track is so selected that the control signal can be recorded and reproduced. The width C of the audio track is so selected that, in the case of portable VTRs, even though a completely satisfactory frequency response is not obtained (about 10 kHz), a satisfactory S/N can be obtained. In like manner, the width F between the audio and video tracks and the width G between the control and video tracks can be determined. Therefore,

When one field is recorded in one track with rotating heads, the signal corresponding to n.sub.H /2 (where n.sub.H is the number of horizontal scanning lines: 525 lines in the NTSC system and 625 lines in the PAL system) is recorded along the width W.

In general, the width M of the front overlapping and the width N of the back overlapping are made equal and are 8 horizontal scanning intervals or 8 H. Therefore, ##EQU1##

Next, referring to FIGS. 1 and 2, the wrapping angle will be described. From FIGS. 1 and 2,

According to the present invention, therefore, the tape 10 is wrapped around the cylinder 3 by 180.degree. plus .theta..sub.1, .theta..sub.2 and .alpha.. To put into another way, the tape 10 is brought into contact with the cylinder 3 along the arc of 180.degree.+.theta..sub.1 +.theta..sub.2 +.alpha..

The front and back overlaps are recorded in order to compensate for not only low outputs at the entrance and exit of the cylinder in both the recording and reproduction modes but also drifts and variations of the head switching in the reproduce mode. According to the present invention, the portion of the tape succeeding the back overlapping track is still wrapped around the cylinder, so that the back overlapping suffices only to compensate for drifts and variations of the head switching in the reproducing mode. Therefore, the width M or N may be 2 or 3H and is not necessary to make .theta..sub.1 equal to .theta..sub.2.

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