I would suggest going back to basics. What does the RX spectrum look like compared to the TX spectrum? Are you doing clock recovery on the RX side, or assuming both sides are synchronized?
Sent from my iPhone > On Mar 26, 2021, at 4:38 PM, Beaudoin, Christopher J > <[email protected]> wrote: > > > Hello Marcus, > > Sorry for the terse nature of my previous message. To be > more specific, the precise symbol rate is 4.608 MHz so the actual sample rate > is 27.648 MHz; the USRP sets the master clock rate to 27.648 MHz when I > command the sample rate. I'm not seeing any overruns at this rate and we > spent a fair bit of time fine tuning the host machine to sustain this data > rate. It will sustain this rate for as long at 10 minutes without reporting > any "O" or "U" errors. I also embed the time stamps into the recorded data > file and post recording analysis does not indicate any time disruptions. > > I'm certain that the mod signal (from my vector signal analyzer) has very low > EVM (~1%) as confirmed with my Rhode Schwartz signal analyzer. I've also > considered saturation of amplifier stages within the AD9361. With 55 dB of > gain, I obtain a rms ADC 16-bit state count of ~15000 for a -40 dBm input > level. As I understand this should be a suitable level given the B210's IIP3 > spec is -20 dBm. I've also reduced the input level at constant gain and didnt > observe any net improvement in the EVM. > > When properly configured, can I expect the B210 to yield an EVM better than > say 5%? > > Chris > > > Creating the usrp device with: num_recv_frames=1024... > [INFO] [UHD] linux; GNU C++ version 5.4.0 20160609; Boost_105800; > UHD_3.11.1.0-0-unknown > [INFO] [B200] Detected Device: B210 > [INFO] [B200] Operating over USB 3. > [INFO] [B200] Initialize CODEC control... > [INFO] [B200] Initialize Radio control... > [INFO] [B200] Performing register loopback test... > [INFO] [B200] Register loopback test passed > [INFO] [B200] Performing register loopback test... > [INFO] [B200] Register loopback test passed > [INFO] [B200] Setting master clock rate selection to 'automatic'. > [INFO] [B200] Asking for clock rate 16.000000 MHz... > [INFO] [B200] Actually got clock rate 16.000000 MHz. > Using Device: Single USRP: > Device: B-Series Device > Mboard 0: B210 > RX Channel: 0 > RX DSP: 0 > RX Dboard: A > RX Subdev: FE-RX2 > RX Channel: 1 > RX DSP: 1 > RX Dboard: A > RX Subdev: FE-RX1 > TX Channel: 0 > TX DSP: 0 > TX Dboard: A > TX Subdev: FE-TX2 > TX Channel: 1 > TX DSP: 1 > TX Dboard: A > TX Subdev: FE-TX1 > > Setting RX Freq: 3199000000.000 Hz... > Actual RX Freq: 3199000000.000 Hz... > > Setting RX Rate: 27648000.000 Sps... > [INFO] [B200] Asking for clock rate 27.648000 MHz... > [INFO] [B200] Actually got clock rate 27.648000 MHz. > Actual RX Rate: 27648000.081 Sps... > > Setting RX Gain: 55.000000 dB... > Actual RX Gain: 55.000000 dB... > > Waiting for "lo_locked": ++++++++++ locked. > > Press Ctrl + C to stop streaming... > > From: Marcus D Leech <[email protected]> > Sent: Friday, March 26, 2021 2:45 PM > To: Julian Arnold <[email protected]> > Cc: Beaudoin, Christopher J <[email protected]>; > [email protected] <[email protected]> > Subject: Re: [USRP-users] Re: B210 EVM > > This e-mail originated from outside the UMass Lowell network. > At 30MSPS are you seeing any overruns? What is your master clock rate? > > Sent from my iPhone > >>> On Mar 26, 2021, at 2:41 PM, Julian Arnold <[email protected]> wrote: >>> >> Chris, >> >> I would say that your EVM is mainly affected by your SNR and your digital >> receiver implementation (AGC / filters / clock recovery / equalizer / ...). >> So without more details it’s going to be hard to say if what you are seeing >> is within limits. >> >> Cheers, >> >> Julian Arnold, M.Sc >> >>> Am 26.03.2021 um 18:29 schrieb [email protected]: >>> >>> >>> I'm capturing a 3 GHz QPSK signal with 5 MHz symbol rate by sampling the >>> signal at 6 times the symbol rate. The B210 is externally referenced to a >>> very clean 10 MHz reference. My measurements of the EVM sampling the signal >>> for ~0.5 seconds are pretty poor ~30-40%. I can provide more setup details >>> but I'm wondering if others can comment on what EVM I can expect. I'm >>> hoping this isn't a fundamental limitation of this hardware system. >>> >>> >>> >>> Thanks, >>> >>> Chris >>> >>> _______________________________________________ >>> USRP-users mailing list -- [email protected] >>> To unsubscribe send an email to [email protected] >> _______________________________________________ >> USRP-users mailing list -- [email protected] >> To unsubscribe send an email to [email protected]
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