Hi Siva,

 there's several thing wrong here:

   * you noticed that the Vert2450 is an 2.4GHz ISM band antenna.
     Why are you using it then? It's not even closely appropriate
     for a 100MHz signal. When using an antenna that is specified
     for roughly 24 times the frequency you're sending on, you will
     get far less power out of the antenna. In your use case
     without the cable, you do, however, don't use the VERT2450 as
     an antenna -- I'd rather think of these two pieces of wire
     (which these monopoles are, really) as a capacitor with some
     parasitic inductance (which models the part of energy that
     doesn't directly get absorbed by the RX antenna).
   * the USRPs and Vert2450 have regular SMA, not Reverse SMA. You
     should be having one center pin too many at the antenna-side
     connector, and one too little on the USRP side.
   * as I said, if you arrange two antennas (no matter which ones,
     really) in a proximity of less than 1% of the RF wavelength,
     they will not work as individual antennas -- power will
     directly couple from one antenna into the other. So your TX
     antenna doesn't radiate into all directions -- it sinks a
     majority of its energy directly into the RX antenna. As much
     as we love SDR, we still bow to Maxwell and Hertz, because we
     can't change physics.
   * In your directly-attached use case, only a little part of the
     TX energy is radiated, whereas in your 5m-distance case,
     you'll get something that more closely resembles the
     unidirectional behaviour of a monopole. Notice that this only
     *very* approximately applies here, as one of the monopoles is
     still attached perpendicular to a ground plane (the B210
     itself), AND both are far too short -- it's pretty impossible
     to predict radiation pattern in this scenario without precise
     simulation, AND 5m is still not far-field for these frequencies.
   * This is real world transmissions, your amplitude will
     fluctuate, especially in a near-field situation with the wrong
     antennas. In fact, your body, holding the vert2450 probably
     increases the efficiency of the VERT2450 for 100MHz
     significantly. You stop your every move and go into an
     anechoic chamber, and you'll get a much more consistent
     amplitude :)
   * 100 MHz relatively easily passes through walls (which is why
     you can get FM radio indoors), so anything that moves in your
     building might be influencing your transmission. Read up on
     fading.

 2/3 c is an approximation of the propagation velocity in a coax
 cable. There's a bit of EM theory behind this, but basically, for
 coax, you get $\frac{c_\text{coax}}{c_0} =
 \frac{1}{\sqrt{\kappa_\text{dielectric}}}$, because the wave
 propagates through the dielectric medium between the inner and
 outer conductor of the cable, in which the speed of light is
 defined by the material's dielectric constant. Solid polyethylene
 is most often found in low-power, high-bandwidth coax, which has a
 $\kappa_\text{PE}\approx 2.25$, and hence, EM waves in these
 cables propagate with $\frac23 c_0$.

 Best regards,
 Marcus

 On 06/05/2015 10:41 AM, siva sankar wrote:

 Hi Marcus,

 We did give more 20db gain but its still the same. I used a
 Reverse SMA male to female antenna extension cable of  50 Ohms
 impedance matched and we are using the ettus Vert 2450 dual ISM
 band antenna.

 In your first response you have taken 2/3 of speed of light,
 could you explain this ? 

 We performed the correlation in the second set-up where one of
 the antenna is 5m away from the first antenna, the peak of the
 correlation is varying and is not constant. Is there any way to
 sort this ? 

 PFA both the configuration set ups. 

 PS: while performing the experiment we fixed the position of the
 antenna(not holding it with hand).

 Thanks 
 Siva

 On Thu, Jun 4, 2015 at 4:01 PM, Marcus Müller
 <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>>
 wrote:

     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 <mailto:USRP-users@lists.ettus.com>
     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

     _______________________________________________
     USRP-users mailing list
     USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com




 -- 
 Thanks and regards
 Siva Sankar.

Hi Siva, > 3. We are using only a 2-RX configuration, we are not transmitting anything and are receiving only standard FM Signals. Ah, I was missing that; nevertheless, when you place the antennas right next to each other, the signals going into them will of course be highly correlated (these two looking more like one antenna two the electromagnetic field than like two separate ones), whereas a wavelength away, you will get a different signal at the antennas. By the way, > We are using these antennas out of compulsion more than anything else. You really shouldn't. A quarter-wave Monopole is really just 75 cm of copper cable connected to the center conductor. I'm pretty sure you can improvise something like that. Best regards, Marcus On 06/05/2015 12:09 PM, siva sankar wrote: > Hi Marcus, > > 1. We are using these antennas out of compulsion more than anything > else. Before we started out, we checked if we could receive 104Mhz > (popular FM Radio Station in India) with this antenna and we were able > to do this well enough to be able to listen to the radio station at > least. But I do understand that the antenna probably is playing a huge > part in our problems. > > 2. We are using suitable connectors to join these antennae to the > board and the cable, so our centre pins are all taken care of :) > > 3. We are using only a 2-RX configuration, we are not transmitting > anything and are receiving only standard FM Signals. > > 4. We will try to procure a more suitable set of antennae and maybe > take our experiment out into an open space as we dont have access to > an anechoic chamber :) > > Thank you for your help > > > On Fri, Jun 5, 2015 at 3:07 PM, Marcus Müller > <marcus.mueller@ettus.com <mailto:marcus.mueller@ettus.com>> wrote: > > Hi Siva, > > there's several thing wrong here: > > * you noticed that the Vert2450 is an 2.4GHz ISM band antenna. > Why are you using it then? It's not even closely appropriate > for a 100MHz signal. When using an antenna that is specified > for roughly 24 times the frequency you're sending on, you will > get far less power out of the antenna. In your use case > without the cable, you do, however, don't use the VERT2450 as > an antenna -- I'd rather think of these two pieces of wire > (which these monopoles are, really) as a capacitor with some > parasitic inductance (which models the part of energy that > doesn't directly get absorbed by the RX antenna). > * the USRPs and Vert2450 have regular SMA, not Reverse SMA. You > should be having one center pin too many at the antenna-side > connector, and one too little on the USRP side. > * as I said, if you arrange two antennas (no matter which ones, > really) in a proximity of less than 1% of the RF wavelength, > they will not work as individual antennas -- power will > directly couple from one antenna into the other. So your TX > antenna doesn't radiate into all directions -- it sinks a > majority of its energy directly into the RX antenna. As much > as we love SDR, we still bow to Maxwell and Hertz, because we > can't change physics. > * In your directly-attached use case, only a little part of the > TX energy is radiated, whereas in your 5m-distance case, > you'll get something that more closely resembles the > unidirectional behaviour of a monopole. Notice that this only > *very* approximately applies here, as one of the monopoles is > still attached perpendicular to a ground plane (the B210 > itself), AND both are far too short -- it's pretty impossible > to predict radiation pattern in this scenario without precise > simulation, AND 5m is still not far-field for these frequencies. > * This is real world transmissions, your amplitude will > fluctuate, especially in a near-field situation with the wrong > antennas. In fact, your body, holding the vert2450 probably > increases the efficiency of the VERT2450 for 100MHz > significantly. You stop your every move and go into an > anechoic chamber, and you'll get a much more consistent > amplitude :) > * 100 MHz relatively easily passes through walls (which is why > you can get FM radio indoors), so anything that moves in your > building might be influencing your transmission. Read up on > fading. > > 2/3 c is an approximation of the propagation velocity in a coax > cable. There's a bit of EM theory behind this, but basically, for > coax, you get $\frac{c_\text{coax}}{c_0} = > \frac{1}{\sqrt{\kappa_\text{dielectric}}}$, because the wave > propagates through the dielectric medium between the inner and > outer conductor of the cable, in which the speed of light is > defined by the material's dielectric constant. Solid polyethylene > is most often found in low-power, high-bandwidth coax, which has a > $\kappa_\text{PE}\approx 2.25$, and hence, EM waves in these > cables propagate with $\frac23 c_0$. > > Best regards, > Marcus > > On 06/05/2015 10:41 AM, siva sankar wrote: > >> Hi Marcus, >> >> We did give more 20db gain but its still the same. I used a >> Reverse SMA male to female antenna extension cable of 50 Ohms >> impedance matched and we are using the ettus Vert 2450 dual ISM >> band antenna. >> >> In your first response you have taken 2/3 of speed of light, >> could you explain this ? >> >> We performed the correlation in the second set-up where one of >> the antenna is 5m away from the first antenna, the peak of the >> correlation is varying and is not constant. Is there any way to >> sort this ? >> >> PFA both the configuration set ups. >> >> PS: while performing the experiment we fixed the position of the >> antenna(not holding it with hand). >> >> Thanks >> Siva >> >> On Thu, Jun 4, 2015 at 4:01 PM, Marcus Müller >> <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> >> wrote: >> >> 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 <mailto:USRP-users@lists.ettus.com> >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com> >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >> >> >> -- >> Thanks and regards >> Siva Sankar. > > > > > -- > Thanks and regards > Siva Sankar.

- you noticed that the Vert2450 is an 2.4GHz ISM band antenna. Why
are you using it then? It's not even closely appropriate for a 100MHz
signal. When using an antenna that is specified for roughly 24 times the
frequency you're sending on, you will get far less power out of the
antenna. In your use case without the cable, you do, however, don't use the
VERT2450 as an antenna -- I'd rather think of these two pieces of wire
(which these monopoles are, really) as a capacitor with some parasitic
inductance (which models the part of energy that doesn't directly get
absorbed by the RX antenna).
- the USRPs and Vert2450 have regular SMA, not Reverse SMA. You
should be having one center pin too many at the antenna-side connector, and
one too little on the USRP side.
 - as I said, if you arrange two antennas (no matter which ones,
really) in a proximity of less than 1% of the RF wavelength, they will not
work as individual antennas -- power will directly couple from one antenna
into the other. So your TX antenna doesn't radiate into all directions --
it sinks a majority of its energy directly into the RX antenna. As much as
we love SDR, we still bow to Maxwell and Hertz, because we can't change
physics.
- In your directly-attached use case, only a little part of the TX
energy is radiated, whereas in your 5m-distance case, you'll get something
that more closely resembles the unidirectional behaviour of a monopole.
Notice that this only *very* approximately applies here, as one of the
monopoles is still attached perpendicular to a ground plane (the B210
itself), AND both are far too short -- it's pretty impossible to predict
radiation pattern in this scenario without precise simulation, AND 5m is
still not far-field for these frequencies.
 - This is real world transmissions, your amplitude will fluctuate,
especially in a near-field situation with the wrong antennas. In fact, your
body, holding the vert2450 probably increases the efficiency of the
VERT2450 for 100MHz significantly. You stop your every move and go into an
anechoic chamber, and you'll get a much more consistent amplitude :)
 - 100 MHz relatively easily passes through walls (which is why you
can get FM radio indoors), so anything that moves in your building might be
influencing your transmission. Read up on fading.

Siva, Regarding the 2 out of 10 non-zero lags, perhaps this is still related to the "set_time" functionality. I understand that presently you have commented out "set_time_now" and that this has largely fixed your issue. Marcus Leech indicated that this would set the time to zero on both channels at startup. I wonder if this is guaranteed?? Another possibility is to use the "set_time_unknown_pps" function that Marcus mentioned. However, Marcus only mentioned using an external PPS. It is also possible to use internal PPS. If you want to try this, use the "set_time_source" function and use "internal". Then call "set_time_unknown_pps" to sync the time for both channels. Perhaps this will eliminate the 2 out of 10 non-zero lags. Rob On Fri, Jun 5, 2015 at 6:45 AM, Marcus Müller <usrp-users@lists.ettus.com> wrote: > Hi Siva, > > > 3. We are using only a 2-RX configuration, we are not transmitting > anything and are receiving only standard FM Signals. > > Ah, I was missing that; nevertheless, when you place the antennas right > next to each other, the signals going into them will of course be highly > correlated (these two looking more like one antenna two the electromagnetic > field than like two separate ones), whereas a wavelength away, you will get > a different signal at the antennas. > > By the way, > > > We are using these antennas out of compulsion more than anything else. > > You really shouldn't. A quarter-wave Monopole is really just 75 cm of > copper cable connected to the center conductor. I'm pretty sure you can > improvise something like that. > > Best regards, > Marcus > > > On 06/05/2015 12:09 PM, siva sankar wrote: > > Hi Marcus, > > 1. We are using these antennas out of compulsion more than anything > else. Before we started out, we checked if we could receive 104Mhz (popular > FM Radio Station in India) with this antenna and we were able to do this > well enough to be able to listen to the radio station at least. But I do > understand that the antenna probably is playing a huge part in our > problems. > > 2. We are using suitable connectors to join these antennae to the board > and the cable, so our centre pins are all taken care of :) > > 3. We are using only a 2-RX configuration, we are not transmitting > anything and are receiving only standard FM Signals. > > 4. We will try to procure a more suitable set of antennae and maybe take > our experiment out into an open space as we dont have access to an anechoic > chamber :) > > Thank you for your help > > > On Fri, Jun 5, 2015 at 3:07 PM, Marcus Müller <marcus.mueller@ettus.com> > wrote: > >> Hi Siva, >> >> there's several thing wrong here: >> >> - you noticed that the Vert2450 is an 2.4GHz ISM band antenna. Why >> are you using it then? It's not even closely appropriate for a 100MHz >> signal. When using an antenna that is specified for roughly 24 times the >> frequency you're sending on, you will get far less power out of the >> antenna. In your use case without the cable, you do, however, don't use the >> VERT2450 as an antenna -- I'd rather think of these two pieces of wire >> (which these monopoles are, really) as a capacitor with some parasitic >> inductance (which models the part of energy that doesn't directly get >> absorbed by the RX antenna). >> - the USRPs and Vert2450 have regular SMA, not Reverse SMA. You >> should be having one center pin too many at the antenna-side connector, and >> one too little on the USRP side. >> - as I said, if you arrange two antennas (no matter which ones, >> really) in a proximity of less than 1% of the RF wavelength, they will not >> work as individual antennas -- power will directly couple from one antenna >> into the other. So your TX antenna doesn't radiate into all directions -- >> it sinks a majority of its energy directly into the RX antenna. As much as >> we love SDR, we still bow to Maxwell and Hertz, because we can't change >> physics. >> - In your directly-attached use case, only a little part of the TX >> energy is radiated, whereas in your 5m-distance case, you'll get something >> that more closely resembles the unidirectional behaviour of a monopole. >> Notice that this only *very* approximately applies here, as one of the >> monopoles is still attached perpendicular to a ground plane (the B210 >> itself), AND both are far too short -- it's pretty impossible to predict >> radiation pattern in this scenario without precise simulation, AND 5m is >> still not far-field for these frequencies. >> - This is real world transmissions, your amplitude will fluctuate, >> especially in a near-field situation with the wrong antennas. In fact, your >> body, holding the vert2450 probably increases the efficiency of the >> VERT2450 for 100MHz significantly. You stop your every move and go into an >> anechoic chamber, and you'll get a much more consistent amplitude :) >> - 100 MHz relatively easily passes through walls (which is why you >> can get FM radio indoors), so anything that moves in your building might be >> influencing your transmission. Read up on fading. >> >> 2/3 c is an approximation of the propagation velocity in a coax cable. >> There's a bit of EM theory behind this, but basically, for coax, you get [image: >> $\frac{c_\text{coax}}{c_0} = \frac{1}{\sqrt{\kappa_\text{dielectric}}}$], >> because the wave propagates through the dielectric medium between the inner >> and outer conductor of the cable, in which the speed of light is defined by >> the material's dielectric constant. Solid polyethylene is most often found >> in low-power, high-bandwidth coax, which has a [image: >> $\kappa_\text{PE}\approx 2.25$], and hence, EM waves in these cables >> propagate with [image: $\frac23 c_0$]. >> >> Best regards, >> Marcus >> >> On 06/05/2015 10:41 AM, siva sankar wrote: >> >> Hi Marcus, >> >> We did give more 20db gain but its still the same. I used a Reverse SMA >> male to female antenna extension cable of 50 Ohms impedance matched and we >> are using the ettus Vert 2450 dual ISM band antenna. >> >> In your first response you have taken 2/3 of speed of light, could you >> explain this ? >> >> We performed the correlation in the second set-up where one of the >> antenna is 5m away from the first antenna, the peak of the correlation is >> varying and is not constant. Is there any way to sort this ? >> >> PFA both the configuration set ups. >> >> PS: while performing the experiment we fixed the position of the >> antenna(not holding it with hand). >> >> Thanks >> Siva >> >> On Thu, Jun 4, 2015 at 4:01 PM, Marcus Müller <usrp-users@lists.ettus.com >> > wrote: >> >>> 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 [image: >>> $\approx\frac{\SI{5}{\meter}}{\frac23 >>> c}=\frac32\frac{\SI{5}{\meter}}{\SI{3e8}{\meter \per >>> \second}}=\SI{25}{\nano\second}$], given you didn't chose wrong >>> cabling. Now, [image: $\SI{104.6}{\mega\hertz}$] 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 [image: $\imp$] (which should be used, as it >>> is the USRP's impedance) and [image: $\wrongimp$] 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 [image: $\imp$] than it should. But >>> still, a [image: $\SI{125}{\ohm}$] 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 listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >>> >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >>> >> >> >> -- >> Thanks and regards >> Siva Sankar. >> >> >> > > > -- > 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 > >