# Forum: DSP Undersampling a band limited signal

 Author: Milruwan Perera (Company: Student) (milprasad) Posted on: 2013-09-09 08:05

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Sir,
I tried to undersample a band limited signal which is 10.7MHz and it's
bandwidth is 200kHz. I undersample the signal and got the signal into
250kHz to 450KHz range.Then I tried to low pass filter the signal(0Hz to
450kHz). But the filtered signal was distorted.

My question is can I under sample a signal and L.P.F the signal in this
way?

Or is there a better way to do undersampling and recover the band
limited signal?

 Author: Christoph Kessler (db1uq) (christoph_kessler) Posted on: 2013-09-09 13:34

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Your frequency range is from 10.6MHz to 10.8 MHz, and the multiple of
your sampling frequency is 350 kHz below or above 10.7 MHz. Which
multiple do you use or what is your real sampling frequency?
I suppose your concept mixes both possible multiples or even more than
two into your "intermediate frequency" band 250...450 kHz which causes
distortion.

 Author: Milruwan Perera (Company: Student) (milprasad) Posted on: 2013-09-09 14:00
Attached files:

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Christoph Kessler (db1uq) wrote:
> what is your real sampling frequency?

The real sampling frequency is 2.5MHz.
Here I attach the spectrum analyzer output, I had got.

 Author: Referee (Guest) Posted on: 2013-12-02 18:23

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With 2.5 MHz sampling frequency you get your signal in baseband between
600 kHz and 800 kHz not 250-450 kHz. See
http://angeloricotta.altervista.org/UndersamplingA...

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