... | ... | @@ -18,6 +18,55 @@ A: You mainly get two things: |
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was a switch reboot in between. Syncing to GPS time on reboot avoids
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that.
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### Q: Is it possible to use White Rabbit systems in different locations and be able to have synchronised time via Satellite link?
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A: Basically as long as the 10 MHz and PPS that you give to the
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different White Rabbit systems are synchronised, WR will keep its
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promises.
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For example, you may synchronise two WR networks by at both ends letting
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a GPS generate the PPS and 10MHz signals, but you will be limited by the
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precision the GPS will give you on those two different locations. This
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may be as good as 3 ns already or maybe better in combination with
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augmentation systems.
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Or you can synchronise your systems with [Time and Frequency Transfer
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using the phase of the GPS
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Carrier](http://tf.nist.gov/time/carrierphase.htm), as CERN has done
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with the CNGS experiment where we could, *after the fact*, synchronise
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related events happening on both sites. The article [Time transfer
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techniques for the synchronisation between CERN and
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LNGS](https://www.ohwr.org/documents/112) explains this.
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If you have Satellite links, you can use Two-Way Satellite Time Transfer
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([TWSTT](http://tf.nist.gov/time/twoway.htm)) and have on both sides a
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system that will provide the PPS and 10 MHz signals. According to the
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presentation [Time transfer through optical
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fibers](http://www.ptb.de/emrp/1393.html?&no_cache=1&cid=2274&did=2820&sechash=9d1ec729),
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page 3 from Mrs. Amy-Klein from LPL, Paris, this can provide an accuracy
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better than 1 ns.
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Using Time Transfer by Laser Link (T2L2) would give you even a sub-ns
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accuracy.
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The [NEAT-FT Workshop on Optical Networks for Accurate Time and
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Frequency Transfer](http://www.ptb.de/emrp/1393.html) held in 2012 may
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give you more ideas and you possibly can find partner institutes that
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can help you with such a
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system.
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### Q: What is the required input level for the 10MHz input on the WRS as a grandmaster?
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A: 0 dBm is fine for the logic inside the switch. It is better an higher
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voltage if you have a sine wave due to better slew rate (noise
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immunity). We used about 10 dBm sine wave with excellent results.
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Author: Mattia
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Rizzi
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### Q: What is the required input level for the PPS input on the WRS as a grandmaster?
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A: 2V minimum on a 50 ohm load, 2.5V is fine. The input is terminated
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with a 50 Ohm, 1% resistor.
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Author: Mattia
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Rizzi
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### Q: When connecting the GPS-PPS or the 10 MHz GPS clock to the WhiteRabbit Switch, do I have to change/configure anything?
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A: Yes, it is documented in the [Note on using WR Switch in Grandmaster
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... | ... | @@ -77,38 +126,6 @@ USB port (up to v. 3.2 switches) or the "FPGA test" USB port in the rear |
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(newer switches). RS232 parameters are 115200,
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8N1.
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### Q: Is it possible to use White Rabbit systems in different locations and be able to have synchronised time via Satellite link?
|
|
|
|
|
|
A: Basically as long as the 10 MHz and PPS that you give to the
|
|
|
different White Rabbit systems are synchronised, WR will keep its
|
|
|
promises.
|
|
|
For example, you may synchronise two WR networks by at both ends letting
|
|
|
a GPS generate the PPS and 10MHz signals, but you will be limited by the
|
|
|
precision the GPS will give you on those two different locations. This
|
|
|
may be as good as 3 ns already or maybe better in combination with
|
|
|
augmentation systems.
|
|
|
Or you can synchronise your systems with [Time and Frequency Transfer
|
|
|
using the phase of the GPS
|
|
|
Carrier](http://tf.nist.gov/time/carrierphase.htm), as CERN has done
|
|
|
with the CNGS experiment where we could, *after the fact*, synchronise
|
|
|
related events happening on both sites. The article [Time transfer
|
|
|
techniques for the synchronisation between CERN and
|
|
|
LNGS](https://www.ohwr.org/documents/112) explains this.
|
|
|
If you have Satellite links, you can use Two-Way Satellite Time Transfer
|
|
|
([TWSTT](http://tf.nist.gov/time/twoway.htm)) and have on both sides a
|
|
|
system that will provide the PPS and 10 MHz signals. According to the
|
|
|
presentation [Time transfer through optical
|
|
|
fibers](http://www.ptb.de/emrp/1393.html?&no_cache=1&cid=2274&did=2820&sechash=9d1ec729),
|
|
|
page 3 from Mrs. Amy-Klein from LPL, Paris, this can provide an accuracy
|
|
|
better than 1 ns.
|
|
|
Using Time Transfer by Laser Link (T2L2) would give you even a sub-ns
|
|
|
accuracy.
|
|
|
The [NEAT-FT Workshop on Optical Networks for Accurate Time and
|
|
|
Frequency Transfer](http://www.ptb.de/emrp/1393.html) held in 2012 may
|
|
|
give you more ideas and you possibly can find partner institutes that
|
|
|
can help you with such a
|
|
|
system.
|
|
|
|
|
|
-----
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## Inter-operability
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... | ... | @@ -626,7 +643,7 @@ content of SFPs memory. |
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-----
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22 February 2017
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10 March 2017
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... | ... | |