Atomic Clock Monitoring Unit (ACMU) subsystem, for the Indian Regional Navigation Satellite System (IRNSS), also known as NAVIC. This unit is a part of Navigation Payload of the IRNSS satellites and derives the 10.23 MHz on-board Master Timing Reference. It’s the brain of the timing system for navigation satellite, using the atomic clock, generating the precious heart beat for navigation payload.

SAC has indigenously developed and qualified ACMU. It is flown in NVS-01 Satellite. This development saves about Rs. 3 Cr per navigation satellite.

Key features include Switch matrix with high isolation to prevent degradation of clock stability, Hybrid PLL for generation of 10.23 MHz output, 44 bit Direct Digital Synthesis (DDS) realized in FPGA with hyper-fine tuning steps to correct frequency drifts of atomic clocks without any degradation of performance, DMTD based Phase meter with 3 ps Noise Floor at 1 s to monitor hot redundant against active clock.