Coherent measurement between multiple units using external clock
Posted: Fri Nov 19, 2021 1:12 pm
Hello.
I want to use the two redpitaya to coherently measure a channel where both boards will be separated by a big distance, the channel being between them. To get proper results, both boards will need a coherent reference clock (we have a working, coherent, distribution system for that) which is why I'm considering the SIGNALlab as it has the option for an external reference clock as the SATA-synchronization interface can't be used because of the large distance between the units.
Synchronization of the measurements is not 100% necessary, but with a similar measurement system, we're using hardware timestamps to have an accurate representation of the relative time delay between both units. This leads me to multiple questions:
A: Does the redpitaya firmware have a builtin timestamp for measurements or would that have to be implemented in the FPGA image?
B: How is the external clock used with the SIGNALlab? I couldn't find anything regarding this in the documentation; Many links I've found using Google were deeplinks leading to 404 Errors as the readthedocs seems to have been refactored some while ago...
C: Does the SDRlab (as an alternative) need exactly 122.88MHz reference or can any clock be used?
D: The Shop lists an impedance transformer. What would the advantage of this be as opposed to a 50Ohm passthrough terminator, are there any existing reference measurements highlighting advantages of one over the other?
Kind regards
Leon
I want to use the two redpitaya to coherently measure a channel where both boards will be separated by a big distance, the channel being between them. To get proper results, both boards will need a coherent reference clock (we have a working, coherent, distribution system for that) which is why I'm considering the SIGNALlab as it has the option for an external reference clock as the SATA-synchronization interface can't be used because of the large distance between the units.
Synchronization of the measurements is not 100% necessary, but with a similar measurement system, we're using hardware timestamps to have an accurate representation of the relative time delay between both units. This leads me to multiple questions:
A: Does the redpitaya firmware have a builtin timestamp for measurements or would that have to be implemented in the FPGA image?
B: How is the external clock used with the SIGNALlab? I couldn't find anything regarding this in the documentation; Many links I've found using Google were deeplinks leading to 404 Errors as the readthedocs seems to have been refactored some while ago...
C: Does the SDRlab (as an alternative) need exactly 122.88MHz reference or can any clock be used?
D: The Shop lists an impedance transformer. What would the advantage of this be as opposed to a 50Ohm passthrough terminator, are there any existing reference measurements highlighting advantages of one over the other?
Kind regards
Leon