On Thu, Apr 26, 2012 at 12:08 AM, Jamie Wo <[email protected]> wrote: > > > On Thu, Apr 26, 2012 at 5:12 AM, wayne roberts <[email protected]> > wrote: > > Hi Wayne, > > Thanks for your reply. My responses are: > > >> >> I was messing with the same thing myself. >> >> First off, i'm not sure the packet decoder outputs in a real-time fashion >> to drive an audio sink. Try a scope sink to see how often the packet >> decoder output updates: is there a better way? > > > > I am not sure the real-time fashion to drive an audio sink either, but > there should be a way to support it, I guess. I ran the flow graph and saw > the update time interval from a scope sink is 3 - 5s . Is this too long? Do > you know what does this update time mean?
Yes, these run in "real-time." If they didn't, you wouldn't be properly able to transmit or receive on an actual piece of hardware. >> On the GMSK demodulator side, I would think its best to observe the signal >> going into the demodulator, from uhd rx source. To see it in time domain, >> you can use Quadrature Demod -> throttle -> scope sink, making sure signal >> is centered at 0 and is reasonable distortion free. To be sure what its >> supposed to look like, you can put on the transmitter side Quadrature Demod >> -> throttle -> scope sink on the output of GMSK modulator. >> >> And of course you can put an FFT sink right on the UHD source to see it in >> frequency domain. On the transmitter side, to UHD sink, I have found the >> GMSK modulator outputs signal level near the maximum, meaning some transient >> peaks could cause clipping on USRP transmitter, so it might be prudent to >> put a multiply const (with 0.99 or so) just before going to UHD sink. > > > I used Quadrature Demod -> throttle -> scope sink on the receiver side to > see the signal going into the GSMK demod after uhd source. Also I > used Quadrature Demod -> throttle -> scope sink after the output of GMSK > mod. The time and frequency domain outputs are attached. Theoretically, > these two output should be similar or the same, However, they are quite > different after travelling over the air. Can you see any problems from the > figures? Don't use a throttle when you have a block that's already setting the rate of your flowgraph. The USRP receiver is controlling that. Having two rate-controllers in there is at best not needed and at worst actually screwing up your receiver. Tom _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
