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Re: [Discuss-gnuradio] USRP data rates

From: Richard Clarke
Subject: Re: [Discuss-gnuradio] USRP data rates
Date: Thu, 09 Aug 2007 16:41:35 +1200
User-agent: Thunderbird (Windows/20070728)

Actually I believe 16MHz is only achieved by reducing the sample bit depth from 16 to 8, which I've read somewhere can be done.

8 Mega complex samples per second -> 8MHz when the real and imaginary parts of the complex sample are each 16 bits wide. (=32Mbytes/sec) 16 Mega complex samples per second -> 16MHz when I/Q are reduced to 8 bits each (=32Mbytes/sec)

Somebody correct me if I'm wrong but I'm pretty sure that's right.


Lisa Creer wrote:
The USRP sales brochure lists as a feature "Capable of processing signals up to 16 MHz wide". I can only figure out how it can process signals up to 8 MHz wide. What am I missing?

Since samples sent across the USB are 16-bit signed integers (16-bit I and 16-bit Q for complex samples) that makes each complex sample size 4 bytes. Since the USB max is 32MB/s, we have a limit of 8MS/s which translates to an effective bandwidth of 8MHz wide.

I noticed that there is another method besides usrp.source_c() to retrieve data from the USRP, it is usrp.source_s(). Is this returning an even smaller sample that would somehow get us to the 16 MHz wide bandwidth? What exactly is this method returning?

Thanks in advance.

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