Design, implementation, and qualification of high-performance time and frequency reference for the MeerKAT telescope

Johan Petrus Burger,Daniele Rovera,Michel Abgrall,Vereesé Van Tonder,Grant Adams,Romeo Reginald Gunther Gamatham,Pierre Uhrich,Renier Siebrits,Sarah Buchner,Zwivhuya Ramudzuli,Geomarr Van Tonder

doi:10.1117/1.jatis.8.1.011013

Abstract

The details of the MeerKAT radio telescope’s time and frequency reference subsystem that enables sampling via low-jitter, low-drift microwave clock signals, and absolute timing (≤5 ns accurate) are discussed. The subsystem’s microwave and pulse per second transmission parts are now fully qualified and commissioned for the ultra high frequency (UHF) and L-bands and also provide for a 100-MHz interface and timing interfaces for S-band receivers that were installed. The subsystem includes a cable measurement system called the Karoo array timing system (KATS). Performance and differences on different bands and seasonal drift of the cable delay measurement of KATS are reported. A time scale called the Karoo Telescope Time (KTT) (which is estimated from tracking a few atomic clocks via new software) and the issuing of timing bulletins to users have been largely implemented and verified. Absolute timing calibration and linkage of KTT to the global positioning system time scale and to different UTC(k) realizations of the Coordinated Universal Time (UTC) instances are described. The subsystem uniquely enables high-fidelity sampling and stable tied array configuration. The latter configuration enables timing and transient science over time spans of 5 to 10 years. Simultaneous subarraying is supported. The backend is unique for radio telescopes in terms of being very deterministic as far as timing is concerned.

Highlights

The time and frequency reference (TFR) for a phased array telescope ensures that all the data collected at the separated receivers are coherent, and that the absolute timing is known at each receiver
The Karoo array timing system (KATS) system has been deployed to the ultra high frequency (UHF)-band digitizers on the same antennae as used by the L-band system
Further verification of the time transfer system from the clocks to digitizers happened via comparing the KATS compensated timing to different antennas to the fringe correlation derived timing, as calculated via the telescope’s correlator–beamformer and science data processor systems

Summary

Introduction

The time and frequency reference (TFR) for a phased array telescope ensures that all the data collected at the separated receivers are coherent, and that the absolute timing is known at each receiver. The TFR consists of an ensemble of atomic clocks, microwave upconversion synthesizers, and transmission equipment to supply a sample clock to the radio receiver digitizers. Global Navigation Satellite System (GNSS) tracking, network protocol, and pulse per second (PPS) timing transmission equipment, as well as true time delay measurement apparatus for connecting to digitizing equipment up to 12 km away from the central digital signal processing and computing building (called the Karoo Array Processor Building or KAPB) are described.

Methods

Results

Conclusion