On 11/11/2020 06:20 PM, Dustin Widmann wrote:
Thanks for the quick response Marcus!
It seems to be fairly frequency dependent. I'm attaching a link to a
data file so y'all can take a look at what I mean. I ran a dense-ish
sweep several times to try to get a feel for how reproducible things
were /etc. The transmitter was retuned at each frequency, but the
receiver was only retuned every 10MHz.
https://u.pcloud.link/publink/show?code=XZviezXZGl5Ypkv46LSVf9l9n1YtOV05z92k
in this file:
* blue or green text = range of datapoints that seem to have
reproducible phase offsets (I alternated between blue and green when I
noticed a "jump" in the value ;; sometimes these jumps were 90/180/270
degree, but often not, and were reproducible regardless)
* orange text = phase offset is off in some consistent manner
(90/180/270 degree jump) and/or reproducible aberrant value
* red text = phase offset seems to be random/garbage
* red background = invalid datapoint (either tone is at unexpected bin
on channel 1, channel 2, or both ;; this is one of the other questions
I was alluding to in my first email, I'm presuming its a separate
issue, but maybe not. It's worth noting that when the tone is observed
at the wrong frequency, the frequency where it is observed is often a
multiple of the reference clock instead)
Dustin
What version of UHD are you using?
I spoke with the original developer of the TwinRX driver, and the
preferred approach to tuning if you want coherence
is to tune it twice with timed commands. The reason for this is that
the number of transactions required to tune the
TwinRx exceeds the size of the X310 command queue, but various things
get cached, so the second attempt will have
fewer commands in the queue, and will go through with all the
appropriate timing.
Since this is on a single X310 platform, and it's TwinRX, you might
consider instead using LO sharing:
https://kb.ettus.com/TwinRX#New_Multi_USRP_Functions
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