NAEB Newsletter (Aug 1958)

E.B.U. Review contains a paper by Dr. P. E. Axon of the Engineering Research Dept, of the B.B.C. which gives technical details of this equipment The B.B.C. version uses ^-inch wide magnetic tape running at a tape speed of 200 inches per second, thus a 20 }/ 2 -inch reel of tape is required to record a 15-minute program. Three tracks are laid down longitudinally on the tape, two of the tracks record the video signal and the third track records the ac¬ companying sound. The three heads are mounted in a single stack so that sound is in sync with picture. A second head stack permits continuous monitoring of sound and picture. In the B.B.C. system, the video signal is split into two frequency bands, 0—100 kc and 100 kc - 3 me. The 0—100 kc video band frequency modulates a carrier which is recorded on one track. The higher video band from 100 kc - 3 me is recorded on the second video track in a conventional manner. The audio signal also modulates an FM carrier of 250 kc. In the recording mode, a servo system locks the speed of the capstan to the frequency of the 50 cycle AC supply by use of a light source, photo cell-dc-amp- lifier combination. In the reproduce mode, the speed of the capstan is controlled by comparing the re¬ corded 50 cycle synchronizing signals with the TV station’s sync signals to derive a correction voltage. In addition to an erase head, there is also a cueing head which has been added to assist in editing taped programs. This editing system is subject to further development. At present the cue head is fed through a separate recording amplifier from a 30 kc oscillator. This frequency is used as a “marking” device by pres¬ sing a “cue” key at the point desired for cutting. This causes a 30 kc burst to be recorded on the sound track, which does not interfere with the subsequent playbacks of the tape at normal tape speed. This “mark,” however, does produce an audible signal when the tape is moved slowly past the reproducing head to provide a way of finding the point marked. The 30 kc signal may also be modulated by a voice signal giving editing instructions or it can be AM modulated by vertical sync pulses so that the precise cutting point on the tape may be located. A splicing jig is provided to assure accuracy in joining the cut ends of the tape together. ***** While we are not aware of any educational FM station using multiplex transmission, in the future this type of transmission might well be used in stereophonic broadcasting. The FCC is taking an¬ other look at multiplexing and attempting to de¬ termine whether additional uses are feasible, ap¬ propriate, or should be permitted in the FM band. Written comments are invited covering seven specific applications of FM multiplex under Docket No. 12517. These should be filed on or before Sep¬ tember 2, 1958. ***** We have an equipment “buy” for an educational station planning to go on a reserved UHF channel. This is equipment for a complete UHF TV station and includes the following: 1) One Continental 1 kw UHF transmitter 18) Chan, diplexer and approximately 400 feet of transmission line 2) One G.E. helical an¬ tenna 3) Two GPL image or- thicon camera chains 4) One GPL PA 505 vi- dicon film camera 5) Two GPL PA 100 16mm projector It also includes sync gen¬ erator, switcher, master mon¬ itors and other miscellaneous equipment. This station was in operation until June 20, 1958 and the equipment is being sold on an as is, where is, condition. The price is $25,000 for the lot. If you are interested in the purchase of this equipment contact the writer of this column. 10 Omaha, Nebraska NEWSLETTER