Logan, make sure you're feeding packed bytes into the DPSK Mod block. That's probably why you're seeing a constellation point at zero, you're feeding in unpacked bytes. That might fix everything.
Rich Sent from my iPad > On Oct 27, 2015, at 8:16 AM, mle...@ripnet.com wrote: > > What does the spectral plot look like? It should look very similar to the TX > side of the house. > > > > > > >> On 2015-10-27 11:10, Washbourne, Logan wrote: >> >> Thanks for the info guys! They are both using antennas btw. I came in this >> morning and turned the RX gain up pretty high, roughly 45dB, and the >> constellation plot on the RX side is starting to look pretty square, which I >> think is a bad sign. My thoughts are that with the increase in gain, there >> is too much noise coming through. >> >> I've been toying with adding in a frequency offset on the TX side. I've been >> adding and subtracting up to 30kHz from the center frequency and I haven't >> seen any improvement in the constellation plot on the RX side. >> >> Another thing that is confusing me, on the TX constellation plot, before it >> gets sent to the USRP, there are 3 groupings, -.5, 0, .5. I'm not sure where >> the 0 points are coming from. Since this is DBPSK, there should only be -.5 >> and .5 groupings right? >> >> Should this exercise be pretty straightforward? >> >> Logan Washbourne >> Electrical Engineering Graduate Student >> (Electromagnetics) >> >>> On Mon, Oct 26, 2015 at 3:12 PM, <mle...@ripnet.com> wrote: >>> Consulting now, the book of armaments, errr, UHD manual: >>> >>> >>> >>> http://files.ettus.com/manual/page_dboards.html#dboards_rfx >>> >>> >>> >>> The RFX series has no TX RF gain control, output magnitude is entirely >>> dependent on baseband magnitude. >>> >>> There's 70dB of gain range on RX, however. So, crank up the RX gain. >>> >>> Also, across 1m, the path loss is about 40dB at 2.5GHz, your TX is probably >>> putting out 5dBm, so at the RX end, that's maybe as much as -35dBm. If your >>> RX is set properly, should be enough to see the signal. >>> >>> >>> >>> >>> >>> >>> On 2015-10-26 15:46, Marcus Müller 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> >>>>> 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 >>>>> https://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 list >>>> 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 >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> 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 >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> 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 > _______________________________________________ > Discuss-gnuradio mailing list > 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
