Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450

[Matt Ettus]

Yongsang Kim wrote:
> Hi, all.
>
> I did single-tone test using USRP2 with RFX2400 and XCVR2450.
> There are some undesired signals in the results.
>
> My single-tone test is as follows:
> - Wired connection between USRP2 and Spectrum analyzer
> - Single-tone is transmitted from USRP2 using the following commands
>    ./usrp2_siggen.py -f xxxx
>    ./usrp2_siggen.py -f xxxx -w xxxx
> - For daughter board, RFX2400, XCVR2450 and Basic TX are tested
> - Newest GNU radio and firmware
> - PC specification (I'm pretty sure that the spec is good enough to
> transmit single-tone stably)
>    -- CPU: Intel core2quad processor Q9550
>    -- Ethernet card: Intel 82567LM Gigabit LAN (PCI express slot)
>    -- Memory: 4GB DDR2 800 MHz SDRAM memory
>
> Except the case of Basic TX, there are some undesired signals in the
> results.
> So, I guess the undesired signals are generated by RFX2400 and XCVR2450,
> not by mother board.
> I'm afraid that the undesired signals cause some kind of distortion of
> desired signal.
> (In fact, when I transmit OFDM signal using XCVR2450, I fail to
> demodulate the received OFDM signal)
>
> The resulting spectrum figures are shown in the following link and I
> marked
> the undesired signals in the figures.


What you are seeing are normal transmitter non-idealities, including DC 
offset (aka carrier feedthrough), and IQ imbalance (aka sideband 
suppression.  These can be improved through tuning, but they are not bad 
as is.  Also, on the XCVR you are seeing the phase noise skirts as well.

Matt


> http://141.223.23.5/Spectrum.zip
>
>
> Short descriptions for each figures are as follows:
>
> 1. File name: RFX2400_2p375GHz_01
>    Used daughter board: RFX2400
>    GNU radio command: ./usrp2_siggen.py -f 2.375e9
>
> 2. File name: RFX2400_2p375GHz_02
>    Used daughter board: RFX2400
>    GNU radio command: ./usrp2_siggen.py -f 2.375e9 -w 2M
>
> 3. File name: XCVR2450_2p52GHz_01
>    Used daughter board: XCVR2450
>    GNU radio command: ./usrp2_siggen.py -f 2.52e9
>
> 4. File name: XCVR2450_2p52GHz_02
>    Used daughter board: XCVR2450
>    GNU radio command: ./usrp2_siggen.py -f 2.52e9 -w 2M
>
> 5. File name: BasicTX_30MHz_01
>    Used daughter board: Basic TX
>    GNU radio command: ./usrp2_siggen.py -f 30e6
>
> 6. File name: BasicTX_30MHz_02
>    Used daughter board: Basic TX
>    GNU radio command: ./usrp2_siggen.py -f 30e6 -w 2M
>
> I would appreciate that if somebody let me know what is problem of my
> daughter boards or my test.
> Thanks.