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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD I/O Data Types
Date: Wed, 20 Apr 2011 20:04:09 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110307 Fedora/3.1.9-0.39.b3pre.fc14 Thunderbird/3.1.9

You cannot represent a "pure" sinusoid with a real signal. Think e^(jw)
vs Re{e^(jw)} Maybe someone could think of a better way to say this.

All USRP devices input and output complex baseband. You need to
represent your signal in complex baseband. I suggest experimenting by
feeding your signal into the _complex_ fft plotter in grc and see how it
looks spectrally, because thats how your actual spectrum will look when
you transmit, but shifted up by fc Hz.


One could take that real sinusoid, and translate it into the complex plane with a
  Hilbert transform, and there's a block for doing that.

Although, if this is a pre-recorded signal, one could simply do the Hilbert transform "offline", and have the pre-recorded signal be already transformed into the complex

But if Arya is already using a signal-generator block within GRC or C++, they could simply
  use the already-existing complex output type.

The hardware expects signals to be represented in the complex plane, even when there is no negative
  frequency content of said signals.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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