[USRP-users] MIMO bug?

Marcus D. Leech mleech at ripnet.com
Mon Dec 29 16:57:29 EST 2014


On 12/29/2014 04:54 PM, Dan Sego wrote:
> Thank you for the reply, I hope your holiday was a good one.
>
> I should have noted that I do query the motherboards for gain after 
> the code has completed sampling. Results echo the initial read back 
> after gains are set.
>
> As to the GR, no I haven't. Looked at that approach originally and 
> passed as the learning curve looked longer than C++, and I didn't know 
> C++.......
>
> I had considered the gain question but the only control is on the 
> HMC472 attenuator and 6 dB (coarse) and 3.5 dB (fine) in the ADC (if I 
> have the correct model number - ADS62P45 and family and which is not a 
> user control state I suspect). So at 10 dB gain attempted (21.5 dB 
> attenuation) on the master,slave attenuator and ADC defaulting at/to 0 
> dB gain combines to yield ~20 dB of channel offset (slave relative to 
> master and this presumes that the ADC gains are both set in the 
> master). Otherwise, it looks like fixed gain in the remainder of the 
> cascade (the ADA493X and differential driver for the ADC, MGA82563), 
> have I missed something?
>
> The fact that it is always the slave suggests a driver to me.
>
> I haven't yet run over a range of gain settings in MIMO. I'll try that 
> and report back. I'll also try an older UHD release.
>
> Cheers, and thanks again. Dan
There's a variable attenuator in the WBX RX chain, independent of the 
motherboard.

Putting a simple thing together in GRC would be five minutes work, just 
to confirm sanity:

UHD-source-with-2-channels------>2 FFT sinks.


>
> On Mon, Dec 29, 2014 at 1:05 PM, Marcus D. Leech via USRP-users 
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>
>     On 12/29/2014 12:09 PM, Dan Sego via USRP-users wrote:
>>     Good morning to the list.
>>
>>     I have 2 N200 r4 units with WBX daughter cards operating with the
>>     following Win32; Microsoft Visual C++ version 10.0; Boost_105400;
>>     UHD_003.008.000-release. One unit has an internal GPSDO.
>>
>>     In MIMO operation (via the MIMO cable). The slave unit
>>     experiences an unexplained 25 dB of attenuation relative to the
>>     master. This change does not follow the hardware: that
>>     is it tracks the slave.
>>
>>     I am using US HDTV as probing signal: tuning to 575 MHz with fc32
>>     formatted data sampled as 12.5 MCSPS per unit. The code operated
>>     successfully performing data capture to file (though does have
>>     the windows prompt upon completion to terminate). An example
>>     run screen capture is pasted below: the collection operation
>>     involves continuous sampling saving contiguous packets (28) and
>>     skipping 50 for a approximate burst sampling rate of 25 Hz.
>>
>>     Win32; Microsoft Visual C++ version 10.0; Boost_105400;
>>     UHD_003.008.000-release
>>
>>     -- Opening a USRP2/N-Series device...
>>     -- Current recv frame size: 1472 bytes
>>     -- Current send frame size: 1472 bytes
>>     -- Creating WSA UDP transport for 192.168.10.3:49156
>>     <http://192.168.10.3:49156>
>>     -- Creating WSA UDP transport for 192.168.10.3:49158
>>     <http://192.168.10.3:49158>
>>     -- Creating WSA UDP transport for 192.168.10.3:49157
>>     <http://192.168.10.3:49157>
>>     -- Creating WSA UDP transport for 192.168.10.3:49159
>>     <http://192.168.10.3:49159>
>>     -- Detecting internal GPSDO.... Found an internal GPSDO
>>     -- Creating WSA UDP transport for 192.168.10.2:49156
>>     <http://192.168.10.2:49156>
>>     -- Creating WSA UDP transport for 192.168.10.2:49158
>>     <http://192.168.10.2:49158>
>>     -- Creating WSA UDP transport for 192.168.10.2:49157
>>     <http://192.168.10.2:49157>
>>     -- Creating WSA UDP transport for 192.168.10.2:49159
>>     <http://192.168.10.2:49159>
>>     -- Setting references to the internal GPSDO
>>     -- Initializing time to the internal GPSDO
>>     Using Devices: Multi USRP:
>>       Device: USRP2 / N-Series Device
>>       Mboard 0: N200r4
>>       Mboard 1: N200r4
>>       RX Channel: 0
>>         RX DSP: 0
>>         RX Dboard: A
>>         RX Subdev: WBXv3 RX+GDB
>>       RX Channel: 1
>>         RX DSP: 0
>>         RX Dboard: A
>>         RX Subdev: WBXv3 RX+GDB
>>       TX Channel: 0
>>         TX DSP: 0
>>         TX Dboard: A
>>         TX Subdev: WBXv3 TX+GDB
>>       TX Channel: 1
>>         TX DSP: 0
>>         TX Dboard: A
>>         TX Subdev: WBXv3 TX+GDB
>>
>>     Actual RX Rate Master: 12.500000 Msps...
>>
>>     Actual RX Rate Slave: 12.500000 Msps...
>>
>>     Actual Gain Master: 10.000000 dB...
>>
>>     Actual Gain Slave: 10.000000 dB...
>>
>>     GPS lock status: locked
>>     GPS epoch time: 1419183071 seconds
>>     -- Successfully tuned to 575.000000 MHz
>>     -- 
>>     -- Successfully tuned to 575.000000 MHz
>>     -- 
>>     Checking LO Lock Master LO: locked...
>>     Checking LO Lock Slave LO: locked...
>>     Checking MIMO Lock MIMO: locked...
>>
>>     sample time first packet2.3000003
>>
>>     full seconds2.3000003
>>
>>
>>     sample time first packet2.34068534
>>
>>     full seconds2.34068534
>>
>>
>>     Done!
>>
>>     I have measured the channel signals of the units individually
>>     and configured for MIMO. Examples of the individual measurements
>>     (power spectra and mean noise power and total signal power are
>>     summarized in slide 1 attached. All runs were made at 10 dB of
>>     gain. Both units were individually exercised from 0 to 30 dB of
>>     gain to have side-by-side responses (indeed one unit is 5 dB less
>>     sensitive which track over gain and both have distinctive and
>>     repeatable gain responses using identical log periodic antennas
>>     and matched length coax).
>>
>>     Slide 2 has the MIMO results in both possible configurations.
>>
>>     Has anyone encountered this? Any suggestions?
>>      regards, Dan Sego
>>
>>
>>     _______________________________________________
>>     USRP-users mailing list
>>     USRP-users at lists.ettus.com  <mailto:USRP-users at lists.ettus.com>
>>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>     The only thing I can think of is that the slave gain isn't being
>     set, despite the messages shown to the contrary.
>
>     Have you tried a GR flow-graph to experiment with this case?
>
>
>
>     -- 
>     Marcus Leech
>     Principal Investigator
>     Shirleys Bay Radio Astronomy Consortium
>     http://www.sbrac.org
>
>
>     _______________________________________________
>     USRP-users mailing list
>     USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
>


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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