On Thu, Oct 14, 2010 at 12:47 PM, Matt Ettus <[email protected]> wrote: > > Probe R201 on all 4 WBX boards with an oscilloscope while running. One > side of the resistor is ground and the other side is the reference clock. > They should all be around the same amplitude, and have the exact same > frequency and phase. > > Matt > > > On 10/14/2010 09:13 AM, Steven Clark wrote: > >> 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 >> >> >> >> Matt-
Sorry for the delay in getting back to you. I took a look at R201 on all dboards as you suggested. All 4 looked fairly similar -- a clean-looking 64MHz sine wave. Amplitudes were close, in the 700-800mV p-p range. Comparing between 2 dboards on the same USRP, the phases matched pretty well (within a few degrees I would say). Comparing from one USRP to the other, there was a definite phase offset (~90degrees). Since the SMA cable bringing the clock from master to slave is a few feet long, this seems reasonable. What's the next step? -Steven
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