EEVblog #1040 - Caesium Beam Frequency Standards - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: November 18, 2017, 10:20:16 pm
content: A look at the Caesium beam time and frequency standards at the Keysight standards lab in Melbourne Australia, with Peter Daly

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 18, 2017, 10:31:40 pm
content: Peter Daly is not well informed about Timekeeping using GPS..This system is frequently synchronized to a primary clock, which itself is synchronized to NIST, afaik, and is participating in the ww net of time keeping clocks.. hp sold GPS receivers, as secondary time standards.I even think, that GPS is an accepted way to have traceable time uncertainty.And it takes some time, about a whole day., to check a cesium clock vs. GPS, due to the inherent jitter of receiving GPS signals.Therefore, you have to monitor continuously, not for a limited period of a day..This time stamping is done quite easily, w/o disturbing the Cs clock, nor the distribution amp.Frank

author: orin
author_rank: Frequent Contributor
timestamp: November 19, 2017, 05:43:34 am
content: NIST has a service that provides traceability to NIST from GPS signals. To quote:"The system uses GPS signals as a reference frequency. The GPS signals provide traceability to NIST, since the same GPS signals received by subscribers are received at NIST and compared to the national frequency standard. The GPS receiver is software controlled and requires no operator attention. Your only requirement is to mount a small antenna in a location which has a clear view of the sky."From:https://www.nist.gov/programs-projects/frequency-measurement-and-analysis-service-fmas

author: KE5FX
author_rank: Super Contributor
timestamp: November 19, 2017, 06:52:27 am
content: Quote from: Dr. Frank on November 18, 2017, 10:31:40 pmI was impressed, myself, with his 5071A that's been powered up continuously since 1994. They must've given him a bit more cesium than usual.

author: eul
author_rank: Newbie
timestamp: November 20, 2017, 09:30:17 am
content: (my first post on eevblog. Dave if you read this, I cant count the number of times your videos made my day, thanks for each and every one of them, keep going.)QuoteGPS is at the time not considered traceable. The reason for this boils down to GPS Time (gps system time) as atimescale NOT being UTC(USNO). GPSTime is steered to UTC(USNO) but that steering process (or any otherintermediate that leads from GPS Time to UTC(USNO)) is a black box to the BIPM's eyes, and a black box in atraceability chain means no traceability (checkhttps://www.bipm.org/en/cipm-mra/for some details)So standalone measurements made between a local reference (your Cs clock) and GPS Time (as realized byyour GPS receiver) are not considered traceable ; traceability requires that you get rid of GPSTime in your traceabilitychain. You do so by subtracting your standalone measurements vs GPSTime to those made simultaneously at theprimary lab you want to establish traceability to (NIST in the US, NPL, in the UK, NMI in Australia,LNE in France... all operate similar services). That is how frequencies (more than time itself) are primarily disseminatedin a traceable way. So my feeling is that in the traceability table at 9:40, there is a missing link between the Cs frequencystandard and the NMI : the traceability of the Cs to TAI probably goes through NMI ; no way that Keysight directly dealswith the BIPM at that point.Still, I am also eager to see the Cesium tank attached to a 5071A running continuously for 23 years)--fm