[Discuss-gnuradio] Strange "UUUU" pattern

Generating: '/home/lab/Documents/simpleTX.py'

Generating: '/home/lab/Documents/simpleTX.py'

Executing: /usr/bin/python2 -u /home/lab/Documents/simpleTX.py

[INFO] [UHD] linux; GNU C++ version 4.8.5 20150623 (Red Hat 4.8.5-36); Boost_105300; UHD_3.15.0.git-13-g52138314
[INFO] [USRP2] Opening a USRP2/N-Series device...
[INFO] [USRP2] Current recv frame size: 1472 bytes
[INFO] [USRP2] Current send frame size: 1472 bytes
[WARNING] [UHD] Unable to set the thread priority. Performance may be negatively affected.
Please see the general application notes in the manual for instructions.
EnvironmentError: OSError: error in pthread_setschedparam
UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU
>>> Done

Folks,

 

I have a simple QPSK modulator feeding its output into the input of my USRP transmitter. I notice two oddities:

1. The status window at the bottom produces a sequence of "U" characters until I stop the run, and
2. The receiver does not detect any presence of any signal (I have a receive process on another computer feeding the output of the RTL SDR to an FFT, and is attached to this email)

 

When I replace the QPSK modulator at my transmitter with a simple cosine generator, the receiver shows the presence of the signal with no problem, and I don't see those strange "U" characters at the source GRC process.

 

Can someone offer suggestions at what I should fix?

 

Thanks,

 

Aaron