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

Marcus D. Leech patchvonbraun at gmail.com
Mon Nov 25 13:48:53 EST 2019

On 11/25/2019 04:32 AM, Julian Ilinca via USRP-users wrote:
> 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.
The two analog channels (antenna ports) on the TVRX2 are separate--they 
can be tuned separately, and go through separate
   mixing pathways down to a "low-IF".  That low-IF is sampled by the 
single two-channel ADC on the motherboard, which creates
   two separate I/Q data streams by converting the low-IF to baseband 
digitally inside the FPGA.  Again, there are TWO channels
   that can  be  created by the TVRX2, and EACH of those channels 
appears to the host as a complex-baseband.

> 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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