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On 06/09/2021 10:11 AM, Skyvalakis
Konstantinos wrote:
I have 2 USRP N200 devices, each one equipped with an SBX
daughterboard.
I am providing 10MHz ref clock and 1 PPS input on both devices
with equal length cables, from an external signal generator.
My application is DoA. Is it possible to do it, with 2 USRP
N200 and the SBX daughterboards?
1) Is the following timed commands code snippet correct for
frequency and phase synchronization of both SBX cards?
self.source = uhd.usrp_source(
",".join(("addr0=192.168.10.2,
addr1=192.168.10.3", "")),
uhd.stream_args(
cpu_format="fc32",
channels=range(2),
),
)
self.source.set_clock_source('external', 0)
self.source.set_time_source('external', 0)
self.source.set_clock_source('external', 1)
self.source.set_time_source('external', 1)
self.source.set_samp_rate(2e6)
self.source.set_time_unknown_pps(uhd.time_spec())
self.source.set_gain(50, 0)
self.source.set_antenna('RX2', 0)
self.source.set_gain(10, 1)
self.source.set_antenna('RX2', 1)
time.sleep(1)
self.source.clear_command_time()
self.source.set_command_time(self.source.get_time_now() +
uhd.time_spec_t(0.1));
self.source.set_center_freq(uhd.tune_request(868e6,0), 0)
self.source.set_center_freq(uhd.tune_request(868e6,0), 1)
time.sleep(0.11)
self.source.clear_command_time()
2) Is there anyway to measure and compensate the offset
between the 2 SBX daughterboards?
3) Can this synchronization problem be tackled easier with a
MIMO cable (since I do have one) ?
Thank you in advance.
Konstantinos
Assuming that you're streaming two channels in a single multi_usrp
object, then this looks OK, except there's no reason for that
time.sleep(0.11) *before* the self.source.clear_command_time().
What magnitude of residual phase-offset are you seeing, and how are
you measuring it?
A MIMO cable won't help with residual phase offset.
The usual way of calibrating this out is to inject a phase-identical
test tone into each channel, and measure the phase offset when
starting up.
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