A colleague and I are sending a simple signal in GNU Radio (sine wave, 1 MHz, amplitude of 1) to the USRP sink and have the center frequency at 500 MHz. The N210 USRP is hooked up to an Agilent spectrum analyzer. On the analyzer we are seeing a weird phenomena every two seconds. At first we see the carrier frequency and two sidebands from the sine wave (see attached normal.gif). Then after two seconds we get two bursts of multiple harmonics (see odd.gif).
The question is, why is this happening? Does the phase of the 1 KHz signal become discontinuous before or after being sent to the USRP?
Thanks,
Jon Fox
normal.GIF
odd.GIF