On 27/03/2025 12:46, Heath Stamm wrote:
Hi, I have an X440 loaded with the X4_200 FPGA image running UHD 4.6.
Using the RFNoC API, I am streaming the same 1 MHz tone into two
channels at the same time (timed command) using a TX streamer going
through the DUC (upsampling from 10.24MSPS to 245.76MSPS) through the
same Radio block (same daughtercard) going out two TX ports connected
to a scope.
While the two channels appear to be phase coherent - that is, their
phase offset from each other doesn’t drift over time - they are not
phase aligned. Furthermore, the phase misalignment changes every time
I rerun the script I am using to run this test.
Is this expected behavior on the X440?
My understanding is that this is currently-expected behavior. I think
R&D have it on their "plate" to address this.
I'll point out that in many phase-coherent systems, like phased-array
antenna systems, interferometers, etc, it is
common to have to calibrate the phase offsets at system start-up, and
from time-time while it is running.
An example that I'm fairly familiar with is the 7-antenna synthesis
array at DRAO in Penticton, BC. They have a system
to actively measure and compensate the phase offsets caused by
different cable-system heating._______________________________________________
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