Phase drift , synchronization multi boards

Projects LimeSDR
#1

my configuartion is based on 2 usb limesdr cards. One contains the transmitter: board number1 + 2 receivers the other 2 other receivers and provides its clock 30.72Mhz to the clock REF input to board number1.
Also the transmitter emits 1 BPSK modulation. By doing the intercorrelation of the signals we see that the phase between two signals of 2 receivers of the same card is constant in time however between 2 receivers of 2 different cards the phase turns quite and or quickly. In addition, the greater the carrier frequency, the faster the phase turns.
My configuration is the default one to which I add the line of code to program the clock ref at 30.72Mhz.

Have you got one idea to program the board to suppress phase shift? Write register or ini file?

Best Regards

1 Like
#2

My memory is a little foggy on this, but I believe that the clock output isn’t actually connected on the board - if you want to use it you need to add a jumper of some sort. My guess would be that your boards have completely independent clocks at present. I believe there is a red led that turns green when the locked to an external clock. You also need a software setting to tell the ‘slave’ board that it should use the external clock.

#3

“J19 connector can also be used to supply external reference clock (fitting R147, removing R137, C354)” from https://wiki.myriadrf.org/LimeSDR-USB_hardware_description#Clock_distribution or Limesdr external clock

#4

Thanks for your answer,

to clarify my setup, I use the “daisy chain” assembly.
I program clk ref input frequency with 30.72Mhz value.
When I disconnect the clock the driver indicates "Undefined / Failure
Reference clock 10.00 MHz
TuneVCO (CGEN) - failed to lock (cmphl! = 0)
SetFrequencyCGEN (80 MHz) failed ".
When I connect I have no error, however there is a drift