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I've noticed that the majority of "amateur" SDRs have ADCs with a sampling rate not higher than 20 MSps, but still the HackRF One for example can scan it's whole frequency range (1MHz to 6GHz) in the same time.

How does that happen?

If a SDR were to have a ADC with a 20MSps sampling rate, it could safely sample a signal with a maximum frequency of 20MHz (if quadrature, 10MHz if else). So basically it could work with signals from 0Hz to 20MHz and that range is shifted with the help of a down converter, but it still remains the same width. Do they work with the Nyquist zones or something, somehow reconstructing the spectrum for frequencies higher than the Nyquist frequency?

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can scan it's whole frequency range (1MHz to 6GHz) in the same time.

How does that happen?

Not at all.

The HackRF (and other SDRs) can just be tuned to arbitrary frequencies, giving you arbitrary coverage (in chunks of sample rate bandwidth at once), but not simultaneous coverage. I'm not quite sure where Mossmann claims that it would, so I think this might be a misunderstanding :)

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  • \$\begingroup\$ What about this then ? The spectrogram shows frequencies with 3GHz bandwidth. thumbs.gfycat.com/ChillyFinishedCardinal-mobile.jpg \$\endgroup\$ – Genwolf Jan 12 at 15:53
  • \$\begingroup\$ easy! You tune, receive, analyze, repeat; then you stitch all together. Notice how the thing says "sweep time" in the bottom? It does exactly that, sweep the spectrum (in steps). It seems to take 0.39s for 3000 steps, which means 130 µs per frequency; that seems doable in terms of time for the LO synthesizer to settle and to accumulate a few samples to average their power. \$\endgroup\$ – Marcus Müller Jan 12 at 16:10
  • \$\begingroup\$ Oh I get it.Thanks ! \$\endgroup\$ – Genwolf Jan 12 at 22:41
  • \$\begingroup\$ see also: this tweet from the head inventor / head behind great scott gadgets. \$\endgroup\$ – Marcus Müller Jan 13 at 9:12

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