Tx and Rx are on their own USRP1s, the daughter board is the RFX2400. They are roughl 3ft apart from each other on a desk. The Rx side is using the RX2 port.
I will definitely try upping the gain when I get back into the office tomorrow. I will check the SMA ports, I didn't configure these myself so I should probably double check them anyways. Logan Washbourne Electrical Engineering Graduate Student (Electromagnetics) On Mon, Oct 26, 2015 at 2:46 PM, Marcus Müller <marcus.muel...@ettus.com> wrote: > 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> > 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>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 >>> listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing >> listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://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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