Hello,
My team and I are doing some experiments with the USRP B210 and NB-IoT
waveforms.
During tests we have observed a few issues with the RF output, that we would
like to understand better, and hopefully fix or mitigate. I must admit that
we are not yet very familiar with USRP SDRs, so I apologize in advance for any
stupid question! There are so many options to tweak the USRP :-) !
This is what we have observed:
1. Apparent RF leakage from RX to TX when idle (i.e. not transmitting the
180 kHz NB-IoT carrier). Our B210 was connected to an RF matrix where other
signals in other channels not immediately adjacent to our center frequency also
exist, and, every time we were not transmitting, some of those signals (a MHz
away) were picked up from the RX and “leaked” into the TX – this could be
observed from a spectrum analyzer connected to the B210 TX and it appears to be
picking up quite a wide bandwidth (more than 5-10 MHz).
* Is this a known issue with the B210 RF frontend?
* Does anyone have any suggestions on how to mitigate it (if even
possible)?
* We tried limiting RX bandwidth as described here
https://files.ettus.com/manual/page_usrp_b200.html#b200_fe_bw , but it seems
not change anything at least when idle. Any ideas?
2. Out-of-band emissions and spectral regrowth: The output NB-IoT carrier
shows quite large out-of-band emissions (~-30 dBc @200 kHz from center
frequency, -50 dBc @400 kHz).
* Could this be due to non-linear distortion caused by the B210 frontend
(AD9361) ?
* Would limiting TX analog bandwidth with set_tx_bandwidth(bw) help here?
* Any other suggestions?
I also have some other general questions...:
1. Even after reading this (https://files.ettus.com/manual/page_power.html )
I am still not super clear about if and how the set_tx_power_reference() (and
rx) affect the gain level. I think understand TX gain setting will obviously
affect the output power though.
2. When talking about multiple "gain stages", how does this translate to the
B210? Different stages of the AD9361 ?
3. How are set_tx_bandwidth and set_rx_bandwidth implemented in practice in
the B210?
Many thanks
Luca
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