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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Sampling rate lower than Nyquist-Shannon frequency? |
Date: | Fri, 29 Jan 2016 13:24:47 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
Hi Pawel, receivers like the RTL dongles first use a mixer to downconvert your signal, in this case from a center frequency of 107.5MHz +- 16kHz to a complex baseband signal around 0Hz. That then only needs to be digitized according the actual signal bandwidth. (In fact, if you can filter well enough, you can even build direct receivers that just use aliasing and don't need mixers. However, adjustable bandpass filtering is much harder than building adjustable LOs and mixers) Then, you're misinterpreting Nyquist: for the complex sampling case, like used in direct conversion receivers like the RTL dongles, f_nyquist = bandwidth = f_sample is sufficient; the double sampling rate applies to real signals and real values coming from ADCs only. Best regards, Marcus On 01/29/2016 12:44 PM, Paweł
Tomaszewski wrote:
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