Re: [Discuss-gnuradio] peak near center freq for noise signal, how to fix it

[Alex Zhang]

Veghihat, Hope this can help you

http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2012-October/005376.html

On Mon, Apr 29, 2013 at 8:24 AM, vegihat vegihat <address@hidden> wrote:

Well as you advice me, i set the --lo-offset=1M , for the following command

    uhd_rx_cfile -a serial=4759a751 -N 100000 -f 2.53G --samp-rate=2M --lo-offset=1M noise.dat -v
   
    However the peak is still there. I give below the output of uhd_rx_cfile.py.
    As you can see the Rx DDC frequency is -2M (if I have understood correctly, it should be 1M,right?  )
   
    Any idea what is the wrong..


linux; GNU C++ version 4.4.5; Boost_104200; UHD_003.005.002-47-g4a860d74

-- Opening a USRP1 device...
-- Using FPGA clock rate of 64.000000MHz...
Using mid-point gain of 45.0 ( 0.0 - 90.0 )
Motherboard: USRP1 (4759a751)
Daughterboard: RFX2400 (no serial, RX2, A:0)
Rx gain: 45.0
Rx baseband frequency: 2.528G
Rx DDC frequency: -2M
Rx Sample Rate: 2M
Receving 100k samples
Writing 32-bit complex floats
Output filename: noise.dat

2013/4/28 Alex Zhang <address@hidden>

I remember that some DC is manually added into the frequency point which can be divided by 5Mhz or 10Mhz? Besides the DC at the your central freq, be aware of that if the lo offset setting makes your bandwidth cover these frequency point, you still can see the peaks.

Hope I am not wrong, at least It seems that I observed that thing before.

On Fri, Apr 26, 2013 at 1:44 PM, Marcus D. Leech <address@hidden> wrote:

On 04/26/2013 02:27 PM, vegihat vegihat wrote:

if i have understand i need to use the --lo-offset of uhd_rx_cfile

i have gave various values to  --lo-offset and only one value has moved the DC offset (--lo-offset=1G) and the plotfft gives many small spikes (maybe this is caused to aliasing, but i am not sure)

which is the rule (value of --lo-offset) to set the DC offset out of my band?

What I do is set my LO offset to about half my bandwidth, so in your case:

--lo-offset 1.0e6

--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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Alex,

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Alex,

Dreams can come true – just believe.