Re : spurious sidelobes with WBX

Hi,

Thank you for your answer. However I am not sure to understand how you
changed
your ant-alias filter because this is something that is implemented in
the USRP
FPGA isn’t it ?

As I said when monitoring the baseband IQ signal produced by the
modulator
beofre going to USRP, I don’t see these sidelobes, they only appear
after USRP.

Is it some rounding problem ? and where does this aliasing come from as
the
signal is centered on 0Hz with no further energy after +/- 750Hz. A
sampling
frequency of 3.2MHz (complex) should be enough. I can try use a lower
interpolation and so use 4MHz instead of 3.2MHz.

Best regards

Mathias


De : Charles B. [email protected]
À : Mathias C. [email protected]
Cc : gnuradio [email protected]
Envoyé le : Mer 4 août 2010, 8h 32min 40s
Objet : Re: [Discuss-gnuradio] spurious sidelobes with WBX

On 03/08/2010 21:50, Mathias C. wrote:
Hello,

I am using the USRP1 + WBX to create a DAB OFDM signal (1.5MHz bandwidth) in VHF

band.
The sampling rate used is 3.2MHz (interpolation 40)

However, there’s something I don’t understand. On the picture attached, you can

see 2 spurious sidelobs that appear at about 2.5MHz from the center (red
arrow).
Mathias C.
opendigitalradio.org

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It looks a bit like this doesn’t it.

These ears on my DVB-T signal were caused by aliasing.
when I changed my anti-alias filter they went away

  • Charles

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