I have an application that implements a simple switched radiometer. I use a pair of "valve" blocks to implement and SPDT switch for the data flow--one branch terminatesw in a variable sink, the other branch terminates in a GUI scope block, and a file sink.
An external python script, via xmlrpc, operates the "switched" variable that switches the flow between the "reference" branch and the live data branch. Switching occurs with a 50% duty cycle. What I discovered is that after only a few seconds of switching, I get errors from USRP2: usrp2: channel 0 not receiving rx_samples() failed Initially, I thought that perhaps it was XMLRPC interfering somehow, so I replaced the switching control with a manual GUI "check box" control. Again, after manually switching after a few seconds, I get the above errors. The bandwidth is quite modest--250KHz, and the variable sink gets a filtered/decimated version of the data flow, so the requisite "python guts" are only being called occasionally, relative to the data rates. So, I switched (no pun intended, tee hee) to a different approach entirely, and that is working fine. No "valves", and no variable sinks. Instead, the input stream is multiplied either by 1 or -1, depending on the value of the "switched" variable, and this is then low-pass filtered via a single-pole IIR filter. That works as you'd expect--the switching hardware isn't in place yet, so it's presenting alternately the "normal" and "negated" versions of the input data to the IIR filter, which is, as you would expect, converged to near zero. There are a plethora of approaches to this problem (a switched radiometer), but I was disappointed that my first try not only didn't work, but seemed to exercise some kind of weird bug in Gnu Radio. I'm running the "as of late last night (July 30th, 2010)" GIT of Gnu Radio, if that matters. I wasn't able to determine whether it was the valves provoking the usrp2 receive errors, or the variable sink, and it seems to be related to the branch that terminates in the variable sink--if I never activate the "switch" so that the data always goes down the "normal" path, the flow-graph just runs and runs normally forever. !Cheers -- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
