Re: Questions about the IF signal processing structure of USRP N210

Hello Ze Zhang:

"according to the second generation USRP structure, only the IF band-pass structure is designed for analog down-conversion." -> Again, this is simply not true.

Most of the second-generation USRPs are traditional direct conversion transceivers (with some exceptions), which is a "Low-pass sampling architecture", not a "IF band-pass sampling architecture". Simply go and look at their schematics; B2x0 series use AD9361, a one-chip direct conversion transceiver, and USRP 2 / N2x0 series motherboards are usually fitted with a traditional direct conversion (or maybe traditional superhet) daughterboards. They all come with low-pass filters. You CAN do band-pass sampling with them (by making custom daughterboards or by extending BasicTX/BasicRX daughterboards), but that is definitely not their default operating modes.

Digital IF (or Low-IF) is totally optional, and can be used to deal with various signal artifacts, such as the DC spike. It can be controlled in software (there are APIs for it), by the operator of the device. It happens before the decimation (for Rx) or after the interpolation (for Tx).

Regards,

Kyeong Su Shin

보낸 사람: Ze Zhang <zezezezzc@gmail.com>
보낸 날짜: 2022년 11월 12일 토요일 오후 8:58
받는 사람: Kyeong Su Shin <ksshin@postech.ac.kr>
참조: discuss-gnuradio@gnu.org <discuss-gnuradio@gnu.org>
제목: Re: Questions about the IF signal processing structure of USRP N210

Hello Kyeong Su Shin

Thanks very much for your kindly reply.

First, the information about the software radio structure contains three kinds, which are Low-pass sampling architecture, RF direct band-pass sampling architecture, and IF band-pass sampling architecture. Among them, according to the second generation USRP structure, only the IF band-pass structure is designed for analog down-conversion.

The N210's structure(reference attachment) contains the DDC notation. And DDC contains the digital down conversion. As you mentioned the low-frequency IF stage is optional. Does this mean that the digital shifting in the IF is to adjust for the bias caused by the previous down-conversion? Or this step can be controlled by command.

Kyeong Su Shin <ksshin@postech.ac.kr> 于2022年11月11日周五 16:52写道：

Hello Ze Zhang:

First, there is a dedeicated mailing list for USRP-specific questions: USRP-users. https://kb.ettus.com/Mailing_Lists

"the information mentioned that the common structure for all USRPs is the IF bandpass sampling structure," -> where did you find this information? This is, in general, not true. USRP N200/N210s, especially, usually default to zero-IF (direct conversion) mode (not always, though).

In case of the USRP N200s/N210s, daughterboards implement the RF/IF (if exists) stages of the transceivers and the motherboards implement the baseband and the digital stages of the transceivers. The daughterboards often do not have any IF stages, and directly convert the signal to the baseband. The motherboards CAN implement a low-frequency IF stage by digitally shifting the baseband signals before the decimation stage. This is optional, and not used by default.

Regards,

Kyeong Su Shin

보낸 사람: Ze Zhang <zezezezzc@gmail.com> 대신 discuss-gnuradio-bounces+ksshin=postech.ac.kr@gnu.org <discuss-gnuradio-bounces+ksshin=postech.ac.kr@gnu.org>
보낸 날짜: 2022년 11월 11일 금요일 오후 3:56
받는 사람: discuss-gnuradio@gnu.org <discuss-gnuradio@gnu.org>
제목: Questions about the IF signal processing structure of USRP N210

Hi,

I am using the URSP N210, and have some questions regarding the internal IF (intermediate frequency) signal processing structure of USRP N210.

In the websites, the information mentioned that the common structure for all USRPs is the IF bandpass sampling structure, and in the previous question(https://lists.gnu.org/archive/html/discuss-gnuradio/2013-09/msg00007.html) it was mentioned that USRP N210 is the common second generation USRP structure.

So is there any difference between the second-generation USRP structure and the digital IF transceiver structure? Also, what is the IF frequency range of the RF signal received by the N210 after analog down-conversion?

Is it possible to get the value of the local oscillator frequency or the value of IF frequency by the setting carrier frequency?

From:	Kyeong Su Shin
Subject:	Re: Questions about the IF signal processing structure of USRP N210
Date:	Sat, 12 Nov 2022 13:12:32 +0000