Optical Television Link Employing a Digitally Modulated Laser
A. A. Goldberg, S. Juchnowycz, J. Rossi
An experimental, through-the-air, digital television link is described. It can carry one NTSC color television picture signal and two high quality sound signals across a distance of 1 km in clear air. The television signal is PCM encoded at 3Fsc = 10.7 MHz, 8 bits/sample. The audio signals are PCM encoded at 31.5 kHz, 14 bits/sample. A new serial digital code called “reverse alternating codeword, non-return to zero” (RAC-NRZ) is described. It consists of complementing every other codeword during the conversion of the video and audio to a serial bit stream. The optical television link employs a gallium aluminum arsenide injection laser at the transmitter and an avalanche photodiode at the receiver. The link is essentially transparent to the PCM encoded signal and it produces excellent quality picture and sound whenever operating above threshold.