[USRP-users] Configuring RX connection type on N210/TVRX2

Julian Ilinca julian.ilinca.fgi at gmail.com
Mon Nov 25 04:32:54 EST 2019


Hello all,

This message is a reply to a previous thread which I started. The contents
of which can be found below.

https://www.mail-archive.com/usrp-users@lists.ettus.com/msg09327.html

My question now concerns what data is actually stored in the final I and Q
components that are sent to the host. The question and the answer are
presented below.

Q1
The daughter-board is set so that one channel retrieves the I component and
the other channel the Q. I retrieved this information with the
uhd_usrp_probe command. In the output under RX0 its says connection type =
Q and on RX1 connection type = I. What command do I have to use to change
connection type of RX0 from Q to I, so that I could have two channels
measuring the real component.

A1
That isn't possible.  Signals are presented to the host as complex
samples.  The TVRX2 *analog hardware* uses a so-called "low-IF"
architecture, and the N210 has a single 2-channel complex ADC.  Each of
those two channels is *hard wired* to go to one of the ADC channels, and
the DDC algorithms in the FPGA convert that to a complex base-band signal
that is then filtered, downsampled, and sent to the host computer.

>From this answer, am I to understand that both of the signals coming from
antenna 1 and 2 respectively are first mixed with a signal provided by the
local oscillator (LO) so that they are separately converted to baseband.
After which the information of the baseband originating from antenna 1 is
stored in the Real part of the complex number and the signal coming from
antenna 2 to imaginary part. And only then then filtering and down sampling
occurs. What I want to know is that are the downsampled and filtered
baseband signals from antenna 1 and 2 preserved in the IQ components
respectively.

Furthermore, as I and Q usually mean in-phase and quadrature component, is
the signal coming from antenna 2 mixed with a LO-signal that has been
shifted by 90 degrees in phase compared to the LO-signal that is mixed with
channel 1.

Thank you again

PS.
I'm sorry, but I could not reply directly to the thread as I did not
receive a response email to my in-box. If someone can instruct me how to
accomplish the reply procedure with gmail, or provide a link with the
relevant information I would be more than happy to use the list as it is
intended to be used.
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