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Re: [Discuss-gnuradio] Help : Where is the demodulation blocks implement

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Help : Where is the demodulation blocks implemented in gnuradio [ GMSK,PSK etc].
Date: Thu, 07 Apr 2011 12:32:48 -0400
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv: Gecko/20110303 Thunderbird/3.1.9

On 07/04/2011 10:34 AM, ton ph wrote:
Hi guys ,
I Just want to confirm a thing regarding the demodulation of the digital dat in the gnuradio as the signals are received from the usrp. The doubt are,
 1. Where is the demodulation is implemented in the gnuradio .
 2. What demodulation is implemented by default in the urp_rx_cfile ...
please do help me someone in clearing my doubts .

Gnu Radio is a generic digital-signal-processing framework. Which includes *many* pre-built processing blocks, including demodulators
  and modulators, correlators, detectors, etc, etc.

There is no *default* demodulation scheme anywhere in the basic architecture, and usrp_rx_cfile is used to simply copy samples as they
  come off the USRP hardware into a file.

The USRP hardware doesn't do any demodulation--the signal you see delivered to the host PC is just filtered/decimated baseband samples as they come off the ADC, appropriately scaled for use inside Gnu Radio. The USRP hardware doesn't know anything about modulation or demodulation, per se. All of that is the responsibility of the host software. Correspondingly, the transmit side of the USRP hardware doesn't *know* anything about modulation, either. It is entirely up to the host software to provide appropriately-modulated samples for the hardware to dutifully turn into analog signals and then (usually) up-convert to the desired RF band of interest. Generally, the host interface operates in "baseband" mode--the (complex) samples are centered at DC.


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