On 03/05/2019 06:01 AM, Koyel Das (Vehere) via USRP-users wrote:
Hi,
I am using USRP 2955 R and I have connected an antenna to one end of a
two channel splitter and connected the other two ports of the splitter
to the two RX1 pors of USRP. I am getting different phase difference
in each run of USRP though in one particular run the phase difference
is constant for all channels. The tuned frequency is 2.4 GHz and
sampling rate is 1 MSps so as expected that channel phase differences
are almost same. But when I stop acquiring data and restart it using
gnuradio or the API, then I am getting again a new value of phase
difference across all channels, which is again same across channels.
Is USRP so unstable that it gives different value of phase difference
for each run for the same frequency, and sampling rate? The setup in
the runs are also the same.
Regards,
Koyel
Koyel Das
Senior – Product Engineer
Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W:
www.vehere.com <http://www.vehere.com/>/
/
/
/This isn't about "instability". It's about the way PLL synthesizers
work, and the fact that by default each channel is using its own
synthesizer.
There are a few things that need to happen:
All the channels you're receiving need to be in the same multi_usrp
block, which, among other things, is a conceptual "synchronization domain".
Use timed-commands for tuning (which is a bit awkward to arrange in
Gnu Radio, you'll have to modify the generated code). This will arrange
for the synthesizers to be given a "resynch" signal at exactly the
same time.
OR
Use the "shared LO" features of the TwinRX cards that are on the 2955.
See the knowledge-base document on the TwinRX and phase-synchronization
here:
https://kb.ettus.com/TwinRX
//
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