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Neela Neela soliton33 at live.comHi 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/baseband-devel/attachments/20130805/e461eb98/attachment.htm>