Re: [Discuss-gnuradio] Problem of using UHD blocks as Tx & Rx

[Jason Abele]

> Why do I receive a sine wave when I transmit a constant?

Probably because the 100MHz reference clocks of your two USRP2s are
slightly different

Here are a few suggestions for being sure that you are locking to your
10MHz reference clock:

If you have not modified the generated python code from your GRC
flowgraph, then you are definitely not locked to refclock.  The
easiest way to fix this would be:
    Use a multi-usrp sink and source from the UHD categorey
    Set the number of motherboards and channels to 1 each
    Use the Sync to Unknow PPS option

I know that is a strange interface, we will put an option to use
external ref clock in an update coming soon to git repositories near
you.

Finally, be sure your refclock meets the power/amplitude requirements
shown here:
http://www.ettus.com/uhd_docs/manual/html/usrp2.html#ref-clock-10mhz
   +5dBm to +20dBm (roughly 1Vpp to 5Vpp)

Jason