Hi list, We are using an Ettus B210 with UHD version 3.8.4. In my previous query to the list for zero lag correlation, Marucs suggested to eliminate set_time_now() which has worked for us. This is working fine when both the receiver antennas are on board(we are getting a peak at zero lag). The idea was if both the receivers are at different distances then when we perform correlation between the received signals then we expected to see some lag in the peak with which to estimate the time difference of arrival of the two signals. While this works marginally well (we see peaks at non zero lag roughly 2 out of 10 attempts) when both antennas are on the board, when one antenna is connected to the board via a 5m cable, the performance drops drastically and nothing meaningful can be observed. Attached are screenshots of the signal amplitude for both cases, with and without the cable. The performance of the latter doesn't improve even at higher gains. USB-3.0 sample rate 15.36Msps rx-frequency 104e6 gain 50db(when antennas on board) upto 70db (when one antenna is 5m away) nsamps=2 million. -- Thanks and regards Siva Sankar.

Hi Siva, 20dB more gain should really do the trick, considering that with 50dB you still seem to be deep in a linear range of the RX amplifiers. I'm pretty sure the B210 is not to blame here -- there's something wrong with your cable or antenna: if you matched your system well, 5m cable should do not much more than delaying your RF signal by $\approx\frac{\SI{5}{\meter}}{\frac23 c}=\frac32\frac{\SI{5}{\meter}}{\SI{3e8}{\meter \per \second}}=\SI{25}{\nano\second}$, given you didn't chose wrong cabling. Now, $\SI{104.6}{\mega\hertz}$ should be covered even by the cheapest coax cabling, so that's probably not the case. What kind of cable are you using? Though the common mixup of $\imp$ (which should be used, as it is the USRP's impedance) and $\wrongimp$ cables only cost about 20% of voltage per interface, there /are/ other impedances out there, and with a bit of bad luck, you might end up with a cable whose impedance is further away fro $\imp$ than it should. But still, a $\SI{125}{\ohm}$ cable would lead to a reflection loss of 60%, so not the order of magnitudes you're seeing. So the next suspect is antenna matching. What kind of antenna are you using? What's its wave impedance at the given frequency? Best regards, Marcus On 06/04/2015 11:32 AM, siva sankar via USRP-users wrote: > Hi list, > > We are using an Ettus B210 with UHD version 3.8.4. > > In my previous query to the list for zero lag correlation, Marucs > suggested to eliminate set_time_now() which has worked for us. This is > working fine when both the receiver antennas are on board(we are > getting a peak at zero lag). > > The idea was if both the receivers are at different distances then > when we perform correlation between the received signals then we > expected to see some lag in the peak with which to estimate the time > difference of arrival of the two signals. > > While this works marginally well (we see peaks at non zero lag roughly > 2 out of 10 attempts) when both antennas are on the board, when one > antenna is connected to the board via a 5m cable, the performance > drops drastically and nothing meaningful can be observed. > > Attached are screenshots of the signal amplitude for both cases, with > and without the cable. The performance of the latter doesn't improve > even at higher gains. > > USB-3.0 > sample rate 15.36Msps > rx-frequency 104e6 > gain 50db(when antennas on board) > upto 70db (when one antenna is 5m away) > nsamps=2 million. > > -- > Thanks and regards > Siva Sankar. > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

I might have misread your email; I was assuming that you didn't change the relative position of the antennas, but only used an additional cable to connect them to the USRP. can you send us a photo of the two configurations you're comparing? Your 104.6MHz signal has a wavelength of about 3m. If you affix both antennas directly to the USRP, you don't get wave propagation between the two antennas. These two antennas would directly couple, since they are in reactive near field, not in far field. Best regards, Marcus On 06/04/2015 12:19 PM, Marcus Müller wrote: > Hi Siva, > > 20dB more gain should really do the trick, considering that with 50dB > you still seem to be deep in a linear range of the RX amplifiers. I'm > pretty sure the B210 is not to blame here -- there's something wrong > with your cable or antenna: > > if you matched your system well, 5m cable should do not much more than > delaying your RF signal by $\approx\frac{\SI{5}{\meter}}{\frac23 > c}=\frac32\frac{\SI{5}{\meter}}{\SI{3e8}{\meter \per > \second}}=\SI{25}{\nano\second}$, given you didn't chose wrong > cabling. Now, $\SI{104.6}{\mega\hertz}$ should be covered even by the > cheapest coax cabling, so that's probably not the case. What kind of > cable are you using? > > Though the common mixup of $\imp$ (which should be used, as it is the > USRP's impedance) and $\wrongimp$ cables only cost about 20% of > voltage per interface, there /are/ other impedances out there, and > with a bit of bad luck, you might end up with a cable whose impedance > is further away fro $\imp$ than it should. But still, a > $\SI{125}{\ohm}$ cable would lead to a reflection loss of 60%, so not > the order of magnitudes you're seeing. > > So the next suspect is antenna matching. What kind of antenna are you > using? What's its wave impedance at the given frequency? > > Best regards, > Marcus > > On 06/04/2015 11:32 AM, siva sankar via USRP-users wrote: >> Hi list, >> >> We are using an Ettus B210 with UHD version 3.8.4. >> >> In my previous query to the list for zero lag correlation, Marucs >> suggested to eliminate set_time_now() which has worked for us. This >> is working fine when both the receiver antennas are on board(we are >> getting a peak at zero lag). >> >> The idea was if both the receivers are at different distances then >> when we perform correlation between the received signals then we >> expected to see some lag in the peak with which to estimate the time >> difference of arrival of the two signals. >> >> While this works marginally well (we see peaks at non zero lag >> roughly 2 out of 10 attempts) when both antennas are on the board, >> when one antenna is connected to the board via a 5m cable, the >> performance drops drastically and nothing meaningful can be observed. >> >> Attached are screenshots of the signal amplitude for both cases, with >> and without the cable. The performance of the latter doesn't improve >> even at higher gains. >> >> USB-3.0 >> sample rate 15.36Msps >> rx-frequency 104e6 >> gain 50db(when antennas on board) >> upto 70db (when one antenna is 5m away) >> nsamps=2 million. >> >> -- >> Thanks and regards >> Siva Sankar. >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >