Can you describe for us what the "loopback kit" comprises? Theres hopefully significant attenuation in the signal path.
On Sep 19, 2013, at 7:53 AM, "Marcus D. Leech" <mle...@ripnet.com> wrote: > On 09/19/2013 10:45 AM, Isdren Gineer wrote: >> I am using N210 USRP's with WBX daughtercards connected with a loopback kit >> implementing a 8-PSK waveform. When I start transmitting, I get a clean >> constellation. After a short time however (~5 sec) it appears that the >> receiver temporarily loses phase lock. The eight point constellation >> degrades such that many points appear in a circle with the same radius as >> the points. The FFT of the signal shows that the noise floor temporarily >> rises. It's as if the amplifier begins to clip or some other non-linear >> process is occurring. After such a 'burst' the constellation appears clean >> again until another burst occurs. Has anybody else observed this behavior? >> Any ideas to what could be the underlying issue? >> >> I am using an multiplier to set the signal amplitude to 0.3 and have the >> gains of the USRP's set to around 7dB. If I use a higher amplitude or >> greater gains, performance degrades quickly. Are there any rules of thumb >> for these settings? Why does the performance degrade with increased values? >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > You're either getting ADC clipping, or your receiver is entering a non-linear > operating region where harmonic distortion starts to happen. > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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