Television Line 21 Encoded Information and its Impact on Receiver Design

A system has been proposed for the transmission of accurate time information during Line 21 of the vertical interval of standard television broadcasts. This paper will desctibe the basic system and its implementation in an approach to digital tuning. Many uses have been suggested for the vertical interval , including test signals, facsimile, etc. The National Bureau of Standards proposes using one of the lines for transmission of digitally encoded time information. The line chosen was originally line 1 but this was subsequently changed to line 21 due to the line 1 bypass used in broadcast processors. The information contained in the code would include -NBS time, local time, channel identification, 64 characters of text and a precise 1 MHz reference signal. The text is intended for deaf viewers, emergency codes, subtitles, network communications, etc.