Time & Frequency Metrology of Commercial White Rabbit Hardware J.A. Sherman ([email protected]), J. Savory, NIST, 325 Broadway, Boulder, CO 80305 What is White Rabbit? Physical basis for its high performance: • Developed at CERN for < 1 ns synchronization over many km • Two-way time transfer over a single (bi-directional) fiber • Employs standard single-mode telecom fiber optics • Calibrated transmission asymmetry scaling with fiber length • Network links support general-purpose Ethernet traffic • Discipline of both clock frequency and time (phase) at remote “slave” • Uses “time aware” concepts from Sync-E and IEEE-1588 (PTP) WR master WR slave Layer 1: PLL syntonization ~ Summary of our findings: ~ • Stability of phase across restarts ~ few ps Master time Master time • Grandmaster-slave-slave2 loopback PPS stability ~ 1 ps @ 1 hour Layer 2: • Grandmaster-slave 10 MHz stability ~ 100 fs @ 3 hours with tight environmental control PTP synchronization • Grandmaster follows input 10 MHz phase • Input pulse-per-second is used once at startup to select 10 MHz zero crossing Tested equipment & methodology: Standard NIST disclaimer: any mention of commercial products is for Stability of WR slave 10 MHz across restarts information only; it does not imply recommendation or endorsement by NIST. White Rabbit nodes: SevenSols WR-LEN (2 SFP port) White Rabbit devices • Input 10 MHz and pulse-per-second (PPS) in “grandmaster” mode • Outputs 10 MHz and pulse-per-second in “slave” mode • Can be configured as “slave” on one port, “master” on other, enabling loopback 10 MHz UTC(NIST) primary WR “grandmaster” { PPS reference signals WR “slave” 10 MHz ~ WR “master” Stability of PPS vs. WR-slave2 loopback PPS TX: 1310 nm RX: 1490 nm TX: 1490 nm RX: 1310 nm 10 MHz { PPS WR “slave 2” Time Interval counters (pulse-per-second measurement): Spectracom Pendulum CNT-91 GuideTech GT668PCIe-1 10 MHz phase measurement: Software defined radio (Ettus N210; “BasicRX” daughterboard) High resolution phase metrology technique described in article linked below. Data acquisition & hardware processing: Sample Digitial down-conversion Averaging decimation FPGA Equipment deployed in typical laboratory environment. Fiber length ~ 300 m. ADC1 high-pass DDC & filters sample NCO PLL formatter & clock network interface DDC decimation ADC2 high-pass outputs Stability of 10 MHz vs. WR-slave & filters Then, in software: Phase subtraction Radians to seconds complex- “Sample-aliased” gain peaking divide Additional information: WR phase-lock-loop servo has gain “peaking” around 20 Hz. White Rabbit Project technical presentations http://www.ohwr.org/projects/white-rabbit/wiki/WRpresentations All equipment in environmental control chamber Oscillator metrology with software defined radio JA Sherman, R Jördens, Rev. Sci. Instrum. 87 054711/1-11 (2016) http://tf.boulder.nist.gov/general/pdf/2816.pdf.