USRP1 + gps reference clock


is it possible to “stabilize” USRP1 clock using external GPS reference
clock of 10MHz?



Modify the usrp so that it is in slave clocking mode. Then feed a GPS
stabilized master clock onto the board. The on board clock is 64 MHz,
but e.g., 60 MHz is known to also work, and it is easier to generate
from 10 MHz.

You basically need to follow these steps:

  • Solder an SMA connector into J2001. This is the clock input. Be
    careful when soldering the SMA connector so you don’t break the
    delicate trace from J2001 to C927.
  • Move R2029 to R2030. This disables the onboard clock. R2029/R2030 is
    a 0-ohm resistor.
  • Move C925 to C926.
  • Remove C924.

The only way to get PPS is to use the gr-gpio firmware, which can be
used to insert digital signals into the least significant bits of I
and Q.