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Re: [Discuss-gnuradio] UHD I/O Data Types

From: Arya Santini
Subject: Re: [Discuss-gnuradio] UHD I/O Data Types
Date: Wed, 20 Apr 2011 16:31:04 -0700

By a real signal, I mean a signal like a real valued sinusoid. Say in
a grc graph, I have this:  signal generator (sine, float o/p) ---->
float to short converter ----> usrp sink (short i/p). In this example,
I'm inputting a stream of shorts representing a pure sine wave to the
usrp module. I wanted to ask how I can do this exactly when I call the
send() to the UHD inside a C++ program? (an array of float values
represent the pure sinusoid, which is the waveform I wish to


On Wed, Apr 6, 2011 at 10:47 PM, Josh Blum <address@hidden> wrote:
> On 04/06/2011 08:42 PM, Arya Santini wrote:
>> Hello..
>> The I/O types defined in the uhd::io_type_t class lists 4 COMPLEX
>> types and a CUSTOM type. What I/O type should I specify in the call to
>> send()/recv() if my baseband signal is real and not complex, say I'm
>> transmitting from a file containing real samples of float type. How is
>> a sample type of real float or real short interpreted and/or converted
>> by the UHD library to shorts over the wire?
> I think this is a misunderstanding. A complex baseband signal represents
> 1/fs bandwidth of spectral content which the USRP will modulate to the
> center frequency -> fc.
> To have a "real" signal is to leave half of your spectrum undefined. Is
> it symmetric about fc? or is it really a complex signal centered at fc+fs/4?
> -Josh
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