Hi, Generally, shouldn't that be: twice the /bandwidth/ of the signal to be sampled?
P-T At 05:48 09.03.2006, you wrote: >Unless you've discovered a new breakthough in sampling, you need a >sampling rate at least twice the highest frequency you want to sample, >hence a 44.1K sampling rate on CD's covers only 20Khz of frequency >resolution, same with the 48Khz sampling rate of DATs ... the extra >4.1Khz or 8Khz in the case of DAT and souncards is a guard frequency >... sure you are sampling two channels but in an IQ setup the second >channel is same frequencies shifted by 90 degrees ... so at a 48Khz >sample rate the very best I can get is 24Khz and even that is pushing >right up to the Nyquist frequency (Sample rate diveded by 2) > >Also most modern converters use a digital scheme for the brickwall >filters a(It prevents phase shifts in the passband, impossible to do >in analog if the cutoff is close to the passband) which changes with >the sample rate and are set a bit below sample rate divided by 2 ... I >know this to be true with the Delta series of soundcard > >Am I missing something here? > >JR > >--- In [email protected], Alberto I2PHD <[EMAIL PROTECTED]> wrote: > > > > jr_dakota wrote: > > > In order to double the bandwidth of an SDR, say from 20Khz ro 40Khz > > > wouldn't you also have to double the IF from 12Khz up to 24Khz (or at > > > least 22Khz)? > > > > > > JR > > > > An IF of 12kHz can of course have components that go from -12 to +12 >kHz, if that IF value is the center of an I/Q band > > downconverted by a quadrature mixer. To process it you need a >sampling rate (theoretical) of 24kHz. Anything more is wasted. > > > > Different is the case of an IF of 12kHz where the lower sideband has >already been suppressed by a previous filter. In > > such case, you could conceptually have an upper sideband that >extends from 12kHz to whatever value you want, and in that > > case the sampling speed can be made higher enough to cope with the >signal bandwidth. > > > > 73 Alberto I2PHD > > > > > > > > > >Yahoo! Groups Links > > > > > > > > >__________ NOD32 1.1435 (20060308) Information __________ > >This message was checked by NOD32 antivirus system. >http://www.eset.com +-----------------------+-----------------------------+ | Per-Tore Aasestrand | E-mail : [EMAIL PROTECTED] | | P.O. Box 1708 Nordnes | Phone : + 47 - 55 32 32 35 | | N-5816 Bergen, Norway | Mobile : + 47 - 92 04 44 76 | +-----------------------+-----------------------------+ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
