Recent Time and Frequency Activities at PTB

Recent activities in the field of time and frequency metrology pursued at PTB are reviewed. Quasi-continuous operation of the cesium fountain frequency standard CSF1 enabled us to assess the performance of the older primary clocks CS1 and CS2 much better than previously possible. On average, the CSF1 and CS2 frequencies deviated by less than 5 parts in 1015 during more than 2 years, which is well within the 1σ uncertainty uB of CS2, 12 parts in 1015. In cooperation with BIPM and timing institutes in the US and Europe, several calibration exercises have been conducted that resulted in an improved calibration of PTB’s time comparison equipment