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Forum: DSP Undersampling a band limited signal


Author: Milruwan Perera (Company: Student) (milprasad)
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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?

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Author: Christoph Kessler (db1uq) (christoph_kessler)
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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)
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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)
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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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