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 Brain <chbr...@btinternet.com>
À : Mathias Coinchon <coinc...@yahoo.com>
Cc : gnuradio <discuss-gnuradio@gnu.org>
Envoyé le : Mer 4 août 2010, 8h 32min 40s
Objet : Re: [Discuss-gnuradio] spurious sidelobes with WBX
On 03/08/2010 21:50, Mathias Coinchon 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).
>
>They are not present when monitoring the spectrum of the baseband IQ signal
>before going to USRP.
>
>They also don't appear when sending a tone signal.
>
>Is there any explanation for this ? and any hint to avoid or reduce it ?
>
>Thank you for your help.
>
>Mathias Coinchon
>opendigitalradio.org
>
> _______________________________________________ Discuss-gnuradio mailing list
>Discuss-gnuradio@gnu.org
>http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
It looks a bit like this doesn't it.
http://tinyurl.com/2vhge7j
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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