1. NMISA Technical Progress Report 2012 Adriaan van Brakel

2. 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

3. 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· and 0.8·10-13 (expected error is 1,4·10-13)

4. 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 phase angle generator
Rise- and fall-time: imported traceability: pulse source calibrated by PTB

5. 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).

6. 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.