The State-of-the-Art Medium Terminal (SAMT) Time and Frequency Distribution System

Abstract

The SAMT Satellite Ground Station Distribution System uses redundant Cesium Frequency Standards in conjunction with automatic signal monitoring and switchover equipment to provide 5 MHz, 1 MHz, 1 PPS, and TOD to converter assemblies and other users at the ground station site. The unique features of the SAMT Distribution System are extremely low vibrational and operationally induced phase and amplitude perturbations and output isolation exceeding 100 dB. Automatic switchover is accomplished by a method which ensures that the phase change at the system timing outputs is less than 0.001 degrees when switching from the on-line to standby atomic standard. Glitch-free performance is obtained by utilizing a dynamic phase matching system which incorporates A to D and D to A converters, and a micrologic memory which automatically slews the output phase of the standby Atomic Standard to agree with that of the on-line unit prior to switchover. A disciplined oscillator provides the 5 MHz, 1 MHz and 1 PPS system outputs with extremely low phase jitter and a noise floor of -170 dBc/Hz. Various sine wave and pulse output signals are fed to the system users by high isolation amplifier modules. Cascode circuitry and careful layout ensures that the isolation between the outputs exceeds 105 dB. This isolation permits changing terminations or removing output cables with less than 1 millidegree