[Discuss-gnuradio] multi usrp, 1 odd channel, HW problem?

Hi all-

I have a multi-usrp setup with 2 USRP 1s and 4 WBX daughtercards. I have performed the clock synching described here: http://gnuradio.org/redmine/wiki/1/MultiUsrp

I'm doing 4-channel receive, using a power splitter to send the same CW signal into all 4 d'cards, and tuning them all identically.

3 of the 4 channels are nicely phase-locked. The 4th seems a little...off.

ClockMasterUSRP (Serial #5821): Side A: "red" channel
ClockMasterUSRP (Serial #5821): Side B: "green" channel
ClockSlaveUSRP (Serial #2087): Side A: "blue" channel
ClockSlaveUSRP (Serial #2087): Side B: "black" channel      <--- problem with this guy

Please see these 3 images to see the problem: http://picasaweb.google.com/steven.p.clark/MultiUsrpGlitches?feat=directlink

You can see the problem in both the frequency domain, and in the time domain.

I tried swapping daughtercards around, and the problem is not tied to any one daughtercard, but rather to slave USRP side B.

Any idea what could be causing this? Shouldn't the same clock be going to both sides of the USRP? (why does blue look fine, but black does not?)

-Steven