Real Signal to I/Q Samples

GNU Radio
1

Hello all, I am helping a colleague with the USRP center frequency
tuning functionality and it is my understanding the signal must contain
I and Q values centered at 0Hz.

A real valued signal is generated independently by another program and
is fed to a GRC script. Is it easy/possible to make a GRC script
downshift the signal to 0 Hz and convert to I and Q values or is there
perhaps an example of this already?

Thank you in advance- Tom

2

On 06/21/2011 05:33 PM, Tom H. wrote:

You can use a Hilbert transform to turn it into a complex-valued signal.

You can then mix it using a complex signal source and a multipler to
downshift it.

3

Thank you Marcus,

For the reverse process what would I use to go from I and Q samples with
the USRP tuned to a real signal at the proper center frequency?

I’m
guessing the signal should remain in complex form and be upshifted
using a multiplier, and then some transform (not sure which one in GRC)

Thank you again! - Tom

— On Tue, 6/21/11, Marcus D. Leech [email protected] wrote:

From: Marcus D. Leech [email protected]
Subject: Re: [Discuss-gnuradio] Real Signal to I/Q Samples
To: [email protected]
Date: Tuesday, June 21, 2011, 11:56 PM

On 06/21/2011 05:33 PM, Tom H. wrote:

        Hello all, I am
          helping a colleague with the USRP center frequency tuning
          functionality and it is my understanding the signal must
          contain I and Q values centered at 0Hz.



          A real valued signal is generated independently by another
          program and is fed to a GRC script. Is it easy/possible
          to make a GRC script downshift the signal to 0 Hz and
          convert to I and Q values or is there perhaps an example
          of this already?



          Thank you in advance- Tom







You can use a Hilbert transform to turn it into a complex-valued
signal.



You can then mix it using a complex signal source and a multipler to
downshift it.

--

Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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4

On 06/21/2011 05:33 PM, Tom H. wrote:

I’ve attached an example that uses a narrow-band, real-only signal
source, with everything running at an arbitrary sample rate of 150Ksps.

It uses a Hilbert transform, followed by a decimate-by-two bandpass
filter.

Without the bandpass filter, there will still be a residual “image”
frequency in the complex output of the Hilbert transform, and since
we’re
decimating by two anyway, I thought I’d put in a bandpass filter.