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Preamble Recording for Automatic or Manual Recorder Alignment
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- 6.13 19-mm Digital Cassette Helical Scan Recording Standards
6.12 Preamble Recording for Automatic or Manual Recorder AlignmentA preamble (or postamble) may be recorded on the same tape as the data signal with known frequency and amplitude elements which will allow automatic or manual alignment of the signal electronics to optimize the performance of the playback system. Reproduce azimuth, equalization, and FM demodulator sensitivity may be adjusted at all available tape speeds. The preamble may be used for manual adjustment of any instrumentation magnetic tape recorder/ reproducer (wide band and double density). Automatic adjustment requires a recorder/ reproducer specifically designed with the capability to automatically adjust one or more of the following: reproduce-head azimuth, amplitude equalization, phase equalization, and FM demodulator sensitivity. The signal source may be internal to the recorder or may be externally generated. 6.12.1 Alignment, Direct Electronics. Direct electronics shall use a 1/11 band edge square wave for both manual and automatic alignment as given in Appendix D. 6.12.2 Alignment, FM Electronics. The FM electronics shall use a 1/11 band edge square wave and ±1.414 Vdc or 0.05 Hz square wave for both manual and automatic alignment as given in Appendix D. 6.13 19-mm Digital Cassette Helical Scan Recording StandardsThese standards are for single-channel high-bit rate helical scan digital recorders using 19 mm tape cassettes. Bit rates of less than 10 megabits per second to 256 megabits per second or greater may be recorded and reproduced by equipment conforming to these standards. Interchange parties must, however, determine the availability at a particular site of the equipment required to meet particular data recording requirements. Compatibility between the recording device and the expected playback equipment must also be considered. 6.13.1 Track Format. The format recorded and reproduced by these systems shall be as specified in American National Standard For Information Systems 19-mm Type ID-1 Recorded Instrumentation Digital Tape Format, ANSI INCITS 175-1999.13 Helical tracks employ azimuth recording wherein the head gap angle with respect to the recorded track center line is 90 + 15 for one scan and 90 15 for the adjacent scan. Figure 6-6 and Table 6-10 show details of the helical tracks and auxiliary longitudinal tracks for control, timing, and annotation in the ID-1 format. 6.13.2 Tape and Cassettes. Magnetic tape and 19-mm cassettes are specified in Chapter 7. The magnetic tape shall meet the requirements for 850 oersted class (68 000 A/M). A tape base thickness of 16 um is normally employed. The recorder/reproducers shall be capable of using 19-mm cassettes that conform to the physical dimensions of medium and large cassettes as shown in Table 6-11. Table 6-11 shows tape capacities and indicates the amount of time available for recording, assuming a data input rate of 240 megabits per second. 6.13.3 Recorder/Reproducer Input and Output. Data input and clock are required. The data input shall be in an 8-bit parallel, byte serial format, and the clock signal will be at the required byte rate. Data output will also be in 8-bit parallel format. 
Figure 6-6. Location and dimensions of recorded tracks.
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