Abstract: A synchronous optical digital transmission system comprises a local interface unit having a phase locked loop circuit that senses and adjusts the phase of the clock signals arriving from the remote unit to match the phase of the principal or local clock so that arriving data bit streams can be directly applied to the local system for further processing. The system is also designed to transmit and receive high speed and low speed data over a single fiber operating in a diplex mode without adverse crosstalk effects by employing non-standard line coding techniques.

Abstract: A low cost, high quality converter for generating an amplitude modulated signal in response to a sequence of digital words representing a modulation signal, such as a video image. The converter receives the sequence of digital words at an input rate. The input sequence of digital words is combined with a sequence of factors at a sample rate to generate a second sequence of digital words at the sample rate representing the amplitude modulated signal. The second sequence of digital words is then converted to the amplitude modulated signal. The sequence of factors is a sequence of cosines of the carrier frequency at the carrier phase angle of 45, 135, 225 and 315 degrees. The value of these cosines are +0.707, -0.707, -0.707, +0.707 respectively. These values are normalized to 1 so that they become a sequence of +1, -1, -1, and +1. Multiplication by the sequence of factors is thus carried out by alternately inverting the input sequence of digital words at one-half the sample rate.