On Sep 10, 2014, at 15:50, Malcolm Robb <[email protected]> wrote:
> I'm currently sampling a 2Mhz digital data stream at 2MHz, so obviously I'm > suffering quite badly from Nyquist issues. Ideally I'd like to sample at > either 4Mhz, or better still 8Mhz. I understand that theoretically I can set > the [RTL2832] dongle to sample at 3.2Mhz, but that data loss is virtually > inevitable. The RTL2832 gives you *complex* (I/Q) samples. This does not exactly change the Nyquist limit of 1 MHz (for a 2 MHz sample rate), but it makes it be *plus or minus* 1 MHz, or 2 MHz in total. If you have a digital radio signal which occupies 2 MHz of bandwidth, you *should* be able to receive it with a RTL dongle, given that: - the signal is strong enough - you are using the 2.4 MHz sample rate, not 2.0 (filters aren't perfect, especially not these ones, so you need some margin above Nyquist) - there is no DC offset (i.e. not E4000 tuner), or you have corrected it, or it doesn't matter for the modulation in question Perhaps you could tell us more about what signal you're trying to receive, and what software you're currently using? (I don't have any answers for the other questions in your message.) -- Kevin Reid <http://switchb.org/kpreid/>
