Vector Source in GRC

GNU Radio
1

I’m having trouble transmitting using the vector source in GRC. I
have it sending [1+1j, 1-1j, -1+1j, -1-1j], repeated, to a USRP2 sink
and scope sink. When run, the information on the scope sink (locally)
looks correct. However, on a second host machine with a another USRP2
connected, the scope output looks like noise. By comparison, using a
signal source transmits the expected values (cosine) properly.

I did have to change the default value of 1 for the amplitude to a
lower value in the cosine signal source for it to transmit properly,
but there was no similar option for that on the vector source. Could
this be the issue? Any other ideas or suggestions?

Thanks for the help!
Scott

2

I bet you are clipping, try scaling those numbers down to say 0.2. The
range of the input on the usrp2 is -1 to 1

-josh

3

Josh

Thanks for the suggestion. It looks like you were right with it
clipping, and scaling it down did the trick.

Now, when looking at it on the other machine, running usrp2_fft.py -S,
the signal (for the vector [0.1], repeating) is a sine wave. What is
making it this?

Thanks again
Scott

4

what frequency is the sine wave? You are probably looking at a slight
frequency offset due to the hardware. You may want to try giving each
usrp2 a common reference clock.

-josh

5

It looks to be about 4900Hz. I’m using the RFX2400 daughterboards on
each usrp2.

Scott