The modem's output is ~30dBm and I have ~30dB of attenuation. I figured that the FFT is showing a lot of power, so the gain wasn't necessary.
Thanks for the idea. Implementing a LPF in front of the resampler doesn't seem to make a difference though. On Wed, Mar 23, 2016 at 1:29 PM, Marcus D. Leech <[email protected]> wrote: > On 03/23/2016 03:14 PM, Tom Golden wrote: > > Here's my flow-graph along with a snapshot of the constellation and FFT. > > Thanks!! > -Tom > > What output level is the RF modem producing? Are you using attenuators > between it and the RF input of the USRP? > > I note that you have the RF gain on your capture set to 0. > > Also, I don't recall whether the polyphase resampler requires that the > input already be Nyquist-limited before it gets resampled. > I know some of the other resamplers do that, otherwise, you get aliases > in your output passband. > > Since you're looking at a 9600BPS signal, you should probably have sampled > this at 250ksps--the lowest rate possible with the N210-- > that makes filtering later less computationally intensive. > > > > > On Wed, Mar 23, 2016 at 1:01 PM, Marcus D. Leech <[email protected]> > wrote: > >> On 03/23/2016 02:48 PM, Tom Golden wrote: >> >>> Hi, >>> >>> I'm a novice gnu radio user. I'm using gnuradio with an Ettus N210 >>> cabled to a modem transmitting GMSK 9600bps. This is just for a test to >>> verify the modem transmit bits. >>> >>> I'm having issues with resampling. The N210 clock can't be set to a >>> multiple of 9600, so I'm attempting to resample. I've tried various >>> mechanisms but the output after resampling to 96000 is too noisy to >>> successfully decode bits. I've tried the GMSK demod block as well as the >>> combination of Quadrature Demod->Clock Recovery MM->Binary Slicer - and >>> neither works. >>> >>> I've also played with the Polyphase clock sync but I don't see any >>> noticeable difference. Can anyone recommend a solution? >>> >>> Thanks!! >>> -Tom >>> >>> For a first step, it would be useful for you to share your flow-graph >> with the list. >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > > > > _______________________________________________ > Discuss-gnuradio mailing > [email protected]https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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