On 02/02/2020 04:40 AM, YENDstudio . via USRP-users wrote:
Hi,
I want to know the actual timestamp of TX and RX signals at the RF
antenna. For this I have add/subtract the group delay introduced by
digital filters in the TX and the RX paths from the UHD timestamp.
Through loopback test, I am able to calculate the aggregate delay, but
cannot know the TX delay and the RX delay separately. The UHD driver
has APIs to get the list of filters used in the signal paths. But my
calculated values do not match with the loopback delay I measured.
Could someone help me with this? I am using USRPB200 set with 30.72
MHz master clock rate and 1.92 MHz sampling rate.
Regards!
So, you use a timed transmit sequence, or you just note the time the
samples left your application? Latency measured through the entire
stack will be MUCH larger, and variable, than if measured using a
timed-command transmit sequence.
Quite apart from the analog delay that Nick has already mentioned,
filter-delay will be "shared" between filters in the FPGA, and filters
in the
AD9361 chip--there's a kind of "shared" DSP going on there. The
AD9361 datasheet might be a fruitful place to look at DUC/DDC filter
latencies within the chip.
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