Hi! * looking at your constellation, relief comes setting in: It looks pretty circular to me; notice how the axes are scaled differently. So no catastrophic IQ imbalance. * the fact that it's circular and not a line is probably the result of the constellation sink not being able to achieve timing synchronization, i.e. it doesn't "know" when a symbol starts * You're right, RX SNR is terrible. However, RX power is very little indeed * Rule of thumb: if(not clipping && in doubt) increase gain; * What exactly is your "RF channel": antennas, direct cable with attenuator? * The mistake I do every few months: Did you connect the antenna/cable to the wrong SMA port?
Best regards, Marcus On 26.10.2015 20:33, Washbourne, Logan wrote: > I looked at the spectrums of both sides and the RX side looks to be > inundated with a lot of noise. I'm not sure if its my environment or > my USRPs, but I really expected to see some resemblance of a signal. I > am posting links to screencaps of the TX and RX sides. > > http://imgur.com/GBTHw8T- TX > http://imgur.com/DBy8gqs - RX > > Logan Washbourne > Electrical Engineering Graduate Student > (Electromagnetics) > > > On Mon, Oct 26, 2015 at 1:31 PM, Marcus Müller > <marcus.muel...@ettus.com <mailto:marcus.muel...@ettus.com>> wrote: > > Can you compare the TX spectrum with the RX spectrum? Maybe it'd > worthwhile to first look at at e.g. 500kHz of RX spectrum to see > whether, due to frequency offset, some of the wanted signal simply > gets cut off; admittedly, with 2S/sym that's not too likely... > > Best regards, > Marcus > > > On 26.10.2015 19:16, Washbourne, Logan wrote: >> I am using 250k! >> >> >> >> Logan Washbourne >> Electrical Engineering Graduate Student >> (Electromagnetics) >> >> >> On Mon, Oct 26, 2015 at 1:05 PM, Marcus Müller >> <marcus.muel...@ettus.com <mailto:marcus.muel...@ettus.com>> wrote: >> >> Hello! >> what's the sampling rate you're using? >> >> Best regards, >> Marcus >> >> >> On 26.10.2015 18:38, Washbourne, Logan wrote: >>> Hello all, >>> >>> I'm trying to take a step back from my previous postings and >>> try a simple approach to try and understand working with >>> over the air communications with the USRPs. Let me know if >>> it would be better to post this in the USRPs-Users list. >>> >>> I'm trying to have a simple TX and simple RX side so I can >>> eliminate and unnecessary complications. >>> >>> The TX side has the following flowgraph: Vector >>> Source(preamble+data)->DPSK Mod(DBPSK,2samples/symbol)-> >>> Multiply Const(.707) -> UHD:USRP SINK(2.448GHz center freq, >>> 10dB default gain) >>> >>> RX Side: UHD:USRP Source(2.448GHz center freq, 10dB gain >>> default) -> DPSK DEMOD(DBPSK, 2 samples/ symbol, rest >>> default values) - > file sink >>> >>> I'm checking the progress of the communication by looking at >>> a constellation plot that is connected directly to the USRP >>> SOURCE block on the receiver side. I'm getting a very >>> elliptical shape, more spread out in the horizontal >>> direction but not by much. I'm also looking at the bits from >>> the receiver side in matlab and my preamble is not showing up. >>> >>> These were the same problems I had when trying to use a >>> correlated system for OTA communications. I feel like I'm >>> missing something really simple. >>> >>> Does anyone know of a simple TX, RX grc setup that I can use >>> to test my USRPs? >>> >>> Again, I really appreciate the help you guys give. >>> >>> Logan Washbourne >>> Electrical Engineering Graduate Student >>> (Electromagnetics) >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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