Dear all, I use 2 USRP2 (one transmission and one reception) with LFTX and LFRX boards. I connected the Tx RF output to the Rx RF input and I am trying to see the symbols I am transmitting for a QPSK modulation. It's seem that my constellation is turning (I am not sure), so it may be due to the drift between the local oscillator of the transmitter and receiver. Can it be due also by the fact that the output power of the LFTX daughter board is not high and then it is too low level for good reception quality. I mean do I need to amplify the LFTX output? Best Regards, Sacha Vrazic

On 01/12/2011 09:41 AM, Sacha Vrazic wrote: > Dear all, > > I use 2 USRP2 (one transmission and one reception) with LFTX and LFRX > boards. > I connected the Tx RF output to the Rx RF input and I am trying to see > the symbols I am transmitting for a QPSK modulation. > > It's seem that my constellation is turning (I am not sure), so it may be > due to the drift between the local oscillator of the transmitter and > receiver. That is exactly it. The two oscillators are not locked, so they will drift. Demodulation always needs to track the frequency and phase offset between the transmitter and receiver since they will not be locked in the real world. Matt