QPSK constellation from baseband signal My IQ sampler is measuring a QPSK carrier at a set frequency/bandwidth (40MSamp/s), but shifts the signal spectrum to baseband. My signal is 1.5Msym/s, but sampling at 1.5Msym/s gives me a constellation of a circle due to the phase difference between the carrier and the IQ sampler clock.

I still need to synchronize to the carrier, but I now have a 0Hz carrier? Do I try a costas loop with a 0Hz center VCO? So far I haven't had much luck. Any ideas? Thanks everyone.
The following depicts a QPSK Carrier Recovery loop that works on the baseband I and Q samples following proper decisions from a Timing Recovery Loop. For more information on this implementation see 

High modulation index PSK - carrier recovery



And for more information on a Timing Recovery implementation that can precede this see: 

Symbol timing synchronization using a high sampling rate

(Copying the links here since the question asked would not lead you easily to the prior titles)