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