[Discuss-gnuradio] strange receiver behaviour with UHD

[Patrik Eliardsson]

Dear List,

We have made a test program using a source and a file sink (see fg.jpg) where 
we are receiving a fixed number of samples (with UHD and USRP2 and WBX-card) 
from an AWGN-generator (constant power -19dB).  If we plot the abs value of the 
received signal we always see a "spike" in the 10 first samples (see fig1) 
before the abs value settles to a more expected value. Sometimes (seldom) there 
is no "spike" but the result is still not as expected, the received data starts 
at a higher level and slopes down during a quite long time before settling to a 
stable level (see fig 2).

Have we missed something or why does this "spike" occur? Is there some 
initialization time in the hardware that we need to take into consideration 
before we start to receive samples (recv) after setting all parameters?

Br,
Patrik

fg.jpg
Description: fg.jpg

fig1.jpg
Description: fig1.jpg

fig2.jpg
Description: fig2.jpg