Design Considerations for a Transmission and Distribution System for SMPTE Time-Code Signals

Richard W. Rodgers

To be able to assign videotape machines to editing systems as they have been to studios and master control areas requires that time-code signals be routed along with the audio and video signals. If the SMPTE time code employs 1200-Hz/2400-Hz frequency-shift keying and search speeds from 1/10 to 100 times normal are needed, the bandwidth required will extend from 120 Hz to 240 kHz or more. In the system described, the transmitted signal comes from an interfacing device in the VTR which provides serial time code as a quasi-balanced complementary signal at transistor-transistor-logic level. Problems of ground-loop hum, crosstalk with adjacent audio circuits, and reduced maximum transmission speed when using a shielded twisted pair were overcome by using a send-processor passive network for the output signal and a time-code reconstitutor for the received signal. Additional possible applications of the system include dubbing the time code along with the audio and video signals when making multiple copies of programs and driving time-code readers that are far from the associated VTR.

Print ISSN
Published
1977-02
Content type
Original Research
DOI
10.5594/J13237