| ... | ... | @@ -38,20 +38,24 @@ UTC. |
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### Was the PTB calibration done with a traveling cesium clock? If so, did you apply relativistic corrections to its time base?
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No it wasn't. The [PTB calibration](https://www.ohwr.org/project/cngs-time-transfer/wikis/Documents/PTB-calibration-report)
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No, it wasn't. The [PTB calibration](https://www.ohwr.org/project/cngs-time-transfer/wikis/Documents/PTB-calibration-report)
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was done with a traveling GPS used for time comparison between metrology
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labs. This unit consists of a GPS receiver GR50, a SR60 Time interval
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Counter (TIC), a GPS antenna, and ~50m of HELIAX foam coaxial
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cable.
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labs. This unit consists of a GR50 GPS receiver, a SR60 Time interval
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Counter (TIC), a GPS antenna, and ~50m of low tempco HELIAX foam coaxial
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cable. This system has been traveling through several metrology labs
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where it has been verified to be stable at the 1ns
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level.
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### What is the impact of the Ionosphere on the accuracy of the time transfer?
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### Why the GPS receivers are installed on the surface?
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It is very convenient to keep an antenna cable length of ~40m, in such a
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It is very convenient to keep an antenna cable length of ~50m, in such a
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way that the ensemble can be dismounted and sent to calibration by
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another lab (PolarRX2e sent to METAS) or another lab can bring a
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traveling GPS to our installations (PTB calibration at CERN and LNGS).
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another lab ([PolarRX2e sent to
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METAS](https://www.ohwr.org/project/cngs-time-transfer/wikis/Documents/METAS-calibration)) or another lab can bring a
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traveling GPS to our installations ([PTB calibration at CERN and
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LNGS](https://www.ohwr.org/project/cngs-time-transfer/wikis/Documents/PTB-calibration-report)).
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## Fiber length calibration
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| ... | ... | @@ -69,12 +73,19 @@ considerations: |
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additional asymmetry of only ~0.1ns on the earth equator. This means
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that a simple two-way scheme over an spare fibber has the potential
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to do a time-transfer between two points separated by 10Km with ~1ns
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accuracy.
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accuracy or better if especial care is taken during the measurement
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and monitoring of the feedback delay is enabled.
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3. Delay paths should include as many components as possible in order
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to reduce any systematic error.
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### These fibers are not length-compensated online. What is the length change throughout the year?
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### These fibers are not length-compensated on-line. What is the length change throughout the year?
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The fibber delay tempco is at the order of 50ps/Km/C. The fibbers in
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Gran Sasso are buried deep underground where temperature changes below
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1C are expected. This represents a maximun change inferiour to 1ns
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thourghout the year in the OPERA fibber. At CERN we have ~2Km of fibber
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between the CERN's Control Room (CCR) and HCA442,
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## Beam Current Transformer cable calibration
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| ... | ... | |
