csete/gqrx — Issue #37: Pink waterfall (symptom)
Author: darrenlong
Created: 2012-02-08 19:20:04+00:00
State: open

After issue 36 (writing to waterfall) was resolved and I fetched the git tip and rebuilt gqrx,, it continued to work normally for me for a short while, then something seemed to go persistently wrong. The symptom was a Pink waterfall - no audio underflows or overflows were reported. Reconnecting the FCD didn't help, nor did rebooting.
The next day I upgraded to the git tip but the issue persisted. The FCD seemed to work OK with gnuradio.

I cloned the git tip again today and tried to figure out what the problem might be with a fresh build, and discovered that if left long enough, the pink waterfall gradually fades down to the usual blue colour and the receiver starts to work. This may take from roughly 30 secs to over perhaps 90 secs, before a sensible level is shown on the FFT plot and waterfall. The dBFS value starts at "inf" and after a while shifts to about 350dBFS then winds down to a sane value after a while.

I notice that the I/Q values shown on stdout have unusual values, which become normal after some time:
```
AVG I/Q: -6.48728e+32/-0.000379419
AVG I/Q: -2.35081e+32/-0.000515609
AVG I/Q: -8.51869e+31/-0.000569706
AVG I/Q: -3.08694e+31/-0.000588061
AVG I/Q: -1.11862e+31/-0.000594157
AVG I/Q: -4.05358e+30/-0.000593843
AVG I/Q: -1.4689e+30/-0.00059447
AVG I/Q: -5.3229e+29/-0.000593402
AVG I/Q: -1.92887e+29/-0.000595783
AVG I/Q: -6.9897e+28/-0.000598192
AVG I/Q: -2.53287e+28/-0.000597032
aUAVG I/Q: -1.47904e+33/-0.000599944
AVG I/Q: -5.35962e+32/-0.000597073
AVG I/Q: -1.94218e+32/-0.000600439
AVG I/Q: -7.03793e+31/-0.000594943
AVG I/Q: -2.55035e+31/-0.000597479
AVG I/Q: -9.24176e+30/-0.000594425
AVG I/Q: -3.34896e+30/-0.000595716
AVG I/Q: -1.21357e+30/-0.00059777
AVG I/Q: -4.39764e+29/-0.000597115
AVG I/Q: -1.59358e+29/-0.000595978
AVG I/Q: -5.77471e+28/-0.000595082
AVG I/Q: -2.09259e+28/-0.000597014
AVG I/Q: -7.58298e+27/-0.00059915
AVG I/Q: -2.74786e+27/-0.000599379
AVG I/Q: -9.9575e+26/-0.000599158
AVG I/Q: -3.60832e+26/-0.000598093
AVG I/Q: -1.30756e+26/-0.000599042
AVG I/Q: -4.73822e+25/-0.000599934
AVG I/Q: -1.717e+25/-0.000597861
AVG I/Q: -6.22194e+24/-0.000598523
AVG I/Q: -2.25466e+24/-0.000599039
AVG I/Q: -8.17025e+23/-0.000594522
AVG I/Q: -2.96067e+23/-0.000597709
AVG I/Q: -1.07287e+23/-0.000599587
AVG I/Q: -3.88777e+22/-0.000597121
AVG I/Q: -1.40882e+22/-0.000597989
AVG I/Q: -5.10517e+21/-0.000596092
AVG I/Q: -1.84998e+21/-0.00059905
```
then later:
```
AVG I/Q: -0.000996173/-0.000599633
AVG I/Q: -0.000994948/-0.0005997
AVG I/Q: -0.000994425/-0.000595451
AVG I/Q: -0.000995082/-0.000597237
AVG I/Q: -0.000993751/-0.0005978
AVG I/Q: -0.000994039/-0.000599771
AVG I/Q: -0.000997688/-0.000597842
AVG I/Q: -0.000993183/-0.000601268
AVG I/Q: -0.000993793/-0.000602623
AVG I/Q: -0.000993176/-0.000597503
AVG I/Q: -0.000994207/-0.000601616
AVG I/Q: -0.000994689/-0.000602554
AVG I/Q: -0.000991886/-0.000602674
AVG I/Q: -0.00099506/-0.000599918
```
Hopefully this report will be of some use. I've been dabbling with gnuradio, grc, gqrx, the FCD and my newly acquired USRP for a week or two now and have a fair amount of confidence that hardware and software builds are good and well configured.