Filtering in baseband spectrum

Neela Neela soliton33 at live.com
Mon Aug 5 20:34:58 UTC 2013


Hi Luca
 
Thanks for your reply.
 
Perhaps I am too old school. But how would one make a frequency shift of 225 KHz without running into issues with the folded image spectrum causing a havoc?
 
Any more indications on  asymmetric filter (complex coefficients) and then shift to origin. is there a link to any page that addresses this in detail.
 
While I am being skpetic about these, I am sure everyone is doing it. How thowugh?
 
Regards

 
> Date: Mon, 5 Aug 2013 17:12:38 +0200
> From: luca at srlabs.de
> To: baseband-devel at lists.osmocom.org
> Subject: Re: Filtering in baseband spectrum
> 
> 
> Hi Neela,
> 
> I find your question a bit off-topic in this mail list,
> but still interesting for SDR geeks.
> 
> The asymmetric spectrum is quite normal when processing
> complex domain signals (I/Q).
> 
> If you are only interested in a part of the spectrum, you
> would normally shift it to the origin and then apply a low-pass filter.
> 
> In your case, you can apply a positive shift of 225 KHz, and then
> a filter with cutoff frequency 75 KHz.
> You can easily apply this transformation with GNU Radio block.
> After that, you can even downsample your signal if needed.
> 
> Other methods to obtain the same result are:
> - apply an asymmetric filter (complex coefficients) and then
>   shift to origin
> - use an FFT filter, and possibly invert the spectrum in baseband
>  
> Cheers,
> 
> LM
> 
 		 	   		  
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