NMISA Technical Progress Report 2012 Adriaan van Brakel

Time and Frequency Laboratory Who are we? Chris Matthee: Section Head (Time, Frequency and Fibre Optics); R&D Metrologist Adriaan van Brakel: R&D Metrologist (Time and Frequency; Fibre Optics) Thembelani Gina: DST-NRF Intern (Time and Frequency; Fibre Optics) Overview: Location: NMISA, CSIR Campus, Pretoria, Gauteng, South Africa Only contributor to UTC in Southern Africa (one of only two in Africa) Standards maintained at better uncertainties than local industry requires cmatthee@nmisa.org avbrakel@nmisa.org

Key infrastructure and UTC(ZA) Local frequency standard: Consists of four commercial, thermal beam caesium atomic clocks One high-performance tube, three long-life tubes Pre-emptive tube replacements done to prevent simultaneous clock failures Used to realise the South African National Timescale (SAST) Time transfer link: Septentrio PolaRx3eTR multi-frequency geodetic receiver (GPS and GLONASS) Currently submit CGGTTS data to BIPM; aim to submit RINEX data soon. UTC(ZA): Currently based on a single clock (inventory TF0004) Maintained to within 5 µs of UTC: time step as required Monthly average frequency error is between 1,1·10-13 and 0.8·10-13 (expected error is 1,4·10-13)

Traceability Measurement parameters: Frequency (and rotational speed): direct comparison against local standard, or indirectly via calibrated phase-locked counters or generators Time interval: measurements performed with counters phase-locked to local frequency standard Phase angle: measurements performed with verified Clarke-Hess 5500 phase angle generator Rise- and fall-time: imported traceability: pulse source calibrated by PTB

Accreditation and CMCs Accredited by the South African National Accreditation Service (SANAS) since July 2003 Previous technical assessors: Dr Peter Fisk (NMIA); Dr Bruce Warrington (NMIA); Dr P. Banerjee (NPLI). Most recent re-assessment: August 2011 Accreditation renewed for: frequency, time interval, rise- and fall-time, phase angle, and rotational speed (contact and non-contact) Calibration and Measurement Capabilities: Listed on BIPM KCDB since January 2011 CMCs for: Frequency; Rise- and fall-time; Time interval (delay).

Research and development Steering of local frequency standard Comply with BIPM requirement to keep UTC(ZA) within 100 ns of UTC Design of auxiliary offset generator and commission with clock ensemble Design and implementation of clock steering algorithm Table-top optical frequency standard Focus is on portability, maintainability and robustness Based on two-photon transition of rubidium atom Fibre laser-based source is being constructed Other research interests: Frequency generation and transfer in radio astronomy (MeerKAT → Square Kilometre Array); Time tagging of electronic events; Time and frequency transfer techniques, towards African timing network and regional comparisons (AFRIMETS); Development of stand-alone systems for low accuracy T&F transfer and remote calibration.