On 12/14/2020 09:44 AM, Nieland, Michael via USRP-users wrote:
Dear all,
we are using two B210 USRP’s to generate and receive DQPSK Signals at
1.53 GHz (two TX and two RX channels). The USRP’s use FW Version 8.0
and FPGA Version 16.0 (Hardware Revision 4). We found that there are
quite significant differences in spurious output between the two tx
channels on the B210. I attached screenshots of my spectrum analyzer
measurements demonstrating this behavior.
A couple of more details about the setup:
- USRP connected and powered via USB3
- No external reference used for the above measurements
- The signals are generated using a GnuRadio flowgraph
The spurious signals are always present and independent of the TX Gain
setting, the digital signal amplitude and the signal frequency. We
observed the same behavior on another B210 USRP. We are assuming this
is hardware related but are wondering if UHD settings also play a role
here and if there is a way to possibly improve the performance of
channel 2 in particular (~20 dB difference at 1.52 GHz spur between
channel 1 and channel 2).
Best regards
Michael Nieland
This is probably just a hardware quirk of the AD9361 chip that forms
nearly the entirety of the RF chain on the B2xx series USRPs.
The spur on the 2nd channel looks like it's still about -40dBc, which I
believe is "in spec" for the AD9361 chip.
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