[USRP-users] Full Duplex w/ X310 & UBX-160

Marcus D. Leech mleech at ripnet.com
Thu Mar 31 20:55:54 EDT 2016


On 03/31/2016 12:01 PM, Dave NotTelling via USRP-users wrote:
> Opps, forgot to reply all.
>
> Also, I am using UHD_003.009.003-0-gf0720677
So, here's a weird suggestion.  Try backing out to UHD 3.9.1


>
> On Thu, Mar 31, 2016 at 11:53 AM, Dave NotTelling <dmp250net at gmail.com 
> <mailto:dmp250net at gmail.com>> wrote:
>
>     Marcus,
>
>          Your diagram is correct.
>
>          I ran the tests you suggested, but there were no changes in
>     the RX display.  For the capture that was saved to a file: I
>     opened it up in Baudline and there was no signal present as
>     expected (should be a nice wide signal there)​​
>
>          Please see the attached pictures (all from Google Drive in
>     case there is an attachment size issue) for the various tests.
>
>          One interesting thing was that if I changed the RX frequency,
>     then the transmitted signal would disappear.  For fun, I tuned to
>     the new RX frequency (~ 750 MHz) and there was my signal.  For
>     some reason tuning the RX side is changing the TX frequency as well.
>
>          Also interesting is that the TX gain appears to do nothing.
>
>          Even stranger was that if I set the RX frequency to 1.001 GHz
>     (same as the default TX freq) and then tried to lower the TX
>     frequency, the signal would no longer be present.  No amount of
>     re-tuning the RX to TX side seems to bring the signal back.  I can
>     increase the TX freq all I want, but it seems that having the TX
>     freq be lower than the RX freq causes something to go bad.  I wish
>     I could upload a video of this, but I'm currently constrained to a
>     cell phone connection and don't have much data left for the next
>     few days =\
>
>         Here are descriptions of some of the attached files:
>
>       * 750M_B200.png - Shows the normal spectrum at 750 MHz (not
>         transmitting) - This is what should be seen on the RX side of
>         things
>       * 1G_B200_idle.png - Shows the normal spectrum at 1 GHz (not
>         transmitting) - Mainly to show that there is nothing present
>         normally
>       * transmitting_no_changes.png - Shows the radio transmitting
>         with no changes to the default values
>       * transmitting_full_tx_gain.png - Showd the radio transmitting
>         with the TX gain cranked all the way (higher than this radio
>         can technically do)
>
>         Hope that makes things a little more clear :)
>
>     Thank you!
>
>     -Dave
>
>
>>     GNU Radio Screenshots
>     <https://docs.google.com/folderview?id=0BzpbYvv0G2kMSkc5Q0NrSGhlVWM&usp=drive_web>
>>
>     On Wed, Mar 30, 2016 at 2:58 PM, Marcus Müller
>     <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>>
>     wrote:
>
>         Hi Dave,
>
>         Marcus & I have been scratching our heads, and I've decided to
>         take a step back and verify we're considering the same system
>         setup; could you confirm my picture describes your setup?
>
>         My gut feeling is that "I can't see any spectrum" might mean
>         that something in the GUI world somehow damaged your fosphor
>         sink.
>         Two questions, or rather three:
>         1. If you replace "fosphor sink (GLFW)" with "Qt GUI Waterfall
>         Sink", does it work?
>         2. If you replace "fosphor sink (GLFW)" with "QT fosphor",
>         does it work?
>         3. If you replace "fosphor sink (GLFW)" with a file sink and
>         analyze the data offline, what about that?
>
>         system
>
>
>         On 30.03.2016 20:15, Dave NotTelling via USRP-users wrote:
>>         I removed the Random Source and GFSK blocks and replaced them
>>         with a single Constant Source block with 0 as the constant
>>         value.  I still cannot see anything on the RX side.
>>
>>         I do have two antennas plugged up. They were right next to
>>         one another, but even after putting one on a 5 foot LMR-240
>>         cable, I still get the same results.  Nothing on the RX side.
>>
>>         I also made sure to specify that the USRP Sink went to the
>>         TX/RX antenna, and the USRP Source went to the RX2 antenna.
>>
>>         On Wed, Mar 30, 2016 at 1:31 PM, <mleech at ripnet.com
>>         <mailto:mleech at ripnet.com>> wrote:
>>
>>             If you transmit all zeros, with the TX gain cranked down,
>>             do you get "proper" RX?
>>
>>             In full-duplex, the RX2 port is used for the RX chain,
>>             and TX/RX for the TX chain, always. otherwise, your RX
>>             LNA would go "poof" as soon as you transmit significant
>>             power.
>>
>>             So you have two antennae setup?  How far apart are they?
>>             Small-signal RF amplifiers (like LNAs) have only so much
>>             linearity headroom, so if there's a 1GHz signal screaming
>>             in the LNA's ear, it'll be hard for the rest of the
>>             system to "see" other frequencies.
>>
>>             On 2016-03-30 13:18, Dave NotTelling wrote:
>>
>>>             I tuned the RX side to simply pick up some known signals
>>>             in the area.
>>>
>>>             On Wed, Mar 30, 2016 at 1:07 PM, <mleech at ripnet.com
>>>             <mailto:mleech at ripnet.com>> wrote:
>>>
>>>                 If you're transmitting at a frequency other than
>>>                 you're receiving at, why would you expect to be able
>>>                 to receive it?  I don't understand.
>>>
>>>                 On 2016-03-30 13:02, Dave NotTelling wrote:
>>>
>>>                     Oh, sorry, I meant that I no longer see the GFSK
>>>                     transmission. I also should have added that I
>>>                     don't get a correct spectrum from the RX side
>>>                     *at all*.  If I disable one of the two chains
>>>                     (disable all TX or RX) then everything works fine.
>>>
>>>                     On Wed, Mar 30, 2016 at 1:00 PM,
>>>                     <mleech at ripnet.com <mailto:mleech at ripnet.com>>
>>>                     wrote:
>>>
>>>                         What do you mean by "it all breaks down"? 
>>>                         Error messages?
>>>
>>>                         On 2016-03-30 12:55, Dave NotTelling wrote:
>>>
>>>                             Marcus,
>>>                                  This is odd then. Please see the
>>>                             attached for my example flow graph in
>>>                             GNU Radio. The basics are that I am
>>>                             transmitting a GFSK (just for giggles)
>>>                             on 1.001 GHz and receiving on 900 MHz. 
>>>                             When the graph starts up, the TX side is
>>>                             working properly.  I can tell this by
>>>                             looking at the output of my B200 which
>>>                             is tuned to 1.001 GHz. The moment I
>>>                             change a parameter (RX/TX gain/freq) it
>>>                             all breaks down.  Is this possibly an
>>>                             issue with the X300/X310 UHD driver
>>>                             and/or GNU Radio gr-uhd?  Or am I just
>>>                             doing something stupid?
>>>                             Thank you!
>>>                             -Dave
>>>
>>>                             On Wed, Mar 30, 2016 at 12:22 PM,
>>>                             <mleech at ripnet.com
>>>                             <mailto:mleech at ripnet.com>> wrote:
>>>
>>>                                 The RX and TX synthesizers are
>>>                                 totally separate on the UBX, so you
>>>                                 can frequency-split however you want.
>>>
>>>                                 The larger the split, the easier it
>>>                                 will be to prevent de-sense between
>>>                                 TX and RX, since it would be easy
>>>                                 to, for example, insert a notch
>>>                                 filter for your TX band into the RX
>>>                                 path, etc.
>>>
>>>                                 On 2016-03-30 11:18, Dave NotTelling
>>>                                 via USRP-users wrote:
>>>
>>>                                     Can I transmit at say 100 MHz
>>>                                     while simultaneously receiving
>>>                                     at say 1 GHz?  If so, can I also
>>>                                     use different sampling rates
>>>                                     between the TX and RX paths? Are
>>>                                     there any existing examples of
>>>                                     how to do simultaneous TX and RX
>>>                                     in GNU Radio?
>>>                                     If this is not possible, then
>>>                                     what is the max frequency
>>>                                     difference?  I was assuming that
>>>                                     if I were transmitting at 1 GHz,
>>>                                     then I could tune the RX side up
>>>                                     and down by half the master
>>>                                     clock rate.
>>>                                     Thank you!
>>>                                     -Dave
>>>
>>>                                     _______________________________________________
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>>>                                     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>
>>
>>
>>
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