1、SMPTE RECOMMENDED PRACTICE Basic System and Transport Geometry Parameters for 1/2=in Type M-2 Format RP 158-1 999 Revision of RP 158-1991 1 Scope This practice specifies the video recording system, scanner parameters, and test conditions for 1/2-in type M-2 helical-scan video tape recorders operatin
2、g with video signals having a typical scanning structure of 525 lines, 59.94 fieldds, 2:l interlace, and utilizing the cassettes specified in ANSVSMPTE 250M. The parameters described in this practice are for reference purposes only and should not be taken as the only method available to attain the s
3、pecifications as de- fined in ANSVSMPTE 249M. 2 Definitions 2.1 scanner: A mechanical assembly containing a drum, rotating pole tips, and tape-guiding ele- ments used to record and reproduce video and PCM audio mode signals. 2.2 drum: A cylindrical column around which the tape is at least partially
4、wrapped in order to form the head-to-tape interface of a video tape recording system. 2.3 upper drum: The part of the drum which is not in contact with the reference edge of the tape. (See figure 1 .) 2.4 lower drum: The pari of the drum which con- tacts the reference edge of the tape and pro- vides
5、 tape-guiding functions. (See figure l .) 2.5 effective drum diameter: The value of drum diameter which yields the actual video and PCM audio record dimensions in a theoretical calcu- lation. This value is equal to or greater than the actual drum diameter. Page 1 of 4 pages 2.6 helix angle: The angl
6、e formed between the path of the rotating pole tips and the tape refer- ence edge guiding system. 2.7 trackangle: The angle formed between the video record and the reference edge of the tape. 2.8 center span tension: A calculated value of the tape tension at a point midway between the tape entrance
7、and exit guides of the scanner in a video tape recording system. 2.9 wrapangle: The angle at the center of the drum rotation subtended by the lines of contact between the drum and the reference edge of the tape. 2.10 lead signal overlap: That portion of the helical record which is required to provid
8、e a duplicate (overlap) recording. 3 General specifications 3.1 Dimensions are in the metric system. 3.2 A basic dimension is a fundamental dimen- sion to which no tolerance is applicable. 3.3 Tests and measurements made on the re- corder to check the parameters specified in this practice shall be m
9、ade under the following atmospheric conditions: Temperature for drum diameter 20C k 0.5“C Temperature for all other tests 20C I 1 .OC Barometric pressure 86 kPa to 106 kPa Conditioning time before testing 24 hours Relative humidity (50%f 2)% Copyright O 1999 by the SOCIETY OF MOTION PICTURE AND TELE
10、VISION ENGINEERS 595 W. Hartsdaie Ave., White Plains, NY 10607 (914) 761-1100 Approved November 5, 1999 RP 15&1999 STD-SMPTE RP LS-ENGL 1917 D 8357401 00037.55 57T II +0.008 Dia 76.000 O Tape -Upper drum -Lower drum Lirection of tape travei (a) Drum and tape wrap c (D c Rotation - Q I - x a Chromina
11、nce r Y 1 Luminance I b I J- I I 4.502 -t 0.008 (Chordal distance) (b) Details of zone Z Figure 1 - Side view of chrominance and luminance pole tips Page 2 or 4 pages RP 15-1999 STD-SMPTE RP ZCiB-ENGL 1799 8357401 00039Sb i217 E 4 Tapespeed The tape speed shall be 67.693 mrns, basic. 5 Representativ
12、e scanner parameters 5.1 Drum diameter and structure The effective drum diameter, tape tension, helix angle, and tape speed taken together completely determine the track angle. Different methods of design andor minor variations in drum diameter and tape tension will produce equivalent recordings for
13、 interchange purposes. 5.1.1 Actual upper drum diameter The actual upper drum diameter shall be 76.000 mm + 0.008 mm - O.Oo0 mm. 5.1 2 Actual lower drum diameter The actual lower drum diameter shall be 76.000 mm + 0.000 mm - 0.008 mm. 5.1.3 Upper drum section The upper drum section shall rotate toge
14、ther with the video heads. 5.2 Scanner pole tips Four circumferential pole tips shall be located as shown in figure 2. 5.2.1 Pole tip projection Each pole tip should project radially 0.035 mm (nomi- nal value) above the upper drum surface. 5.22 Luminance pole tips Two pole tips circumferentially arr
15、anged 180“ f 0.003 apart shall be provided for the luminance sig- nal. 5.2.3 Chrominance pole tips Each luminance pole tip shall have an associated pole tip for the time compressed chrominance signal and the FM audio signals. The chrominance pole tips shall be located at a chordal distance of 4.502
16、mm k 0.008 mm in a counterrotational direction from the associ- ated luminance pole tips, and are axially displaced from the associated luminance pole tips by 0.0390 mm f 0.0015 mm in a direction away from the refer- ence edge of the tape. (See figure lb.) 5.1.4 Center span tension 5.2.4 Channel ide
17、ntification The center span tension shall be 0.31 N 10.05 N. 5.1.5 Helix angle The helix angle formed by the scanner and all asso- ciated tape guides shall be 4.250 & 0.001 O. Suitable means, such as a pulse generator producing one pulse per drum revolution, shall be provided for identifying the one
18、 head pair which records field 1. This pair is identified as channel 1, and the other pair is identified as channel 2. Page 3 of 4 pages 1 Chrominance ?Luminance t Reference) , Direction of upper drum rotation Tape entrance Luminance Tape exit Chrominance CHZ Rec a Figure 2 - Top view of chrominance
19、 and luminance pole tips Annex A (Informative) Bibliography ANSI/SMPTE 249M-1996, Television Analog Recording - 1/2-in Type M-2 - Records ANSIISMPTE 251 M-1996, Television Analog Recording - 1/2-in Type M-2 - Electrical Parameters of Video, Audio, Time and Control Code and Tracking Control ANSIISMPTE 250M-1996, Television Analog Recording - 1/2-in Type M-2 - Tapes and Cassettes ANSIISMPTE 252M-1996, Television Analog Recording - 1/24 Type M-2 - Pulse Code Modulation Audio Page 4 ot 4 Pages
