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 <*> 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/
