Write Tx Data and Sampling

[krmills]

Hello all,

I was curious about what if any sampling is done by the Write Tx Data block. In the example code niUSRP EX Tx Continuous Async.vi Two sine waveforms are combined to make a complex exponential. This complex exponential is passed into the Write Tx Data block. My question becomes this: does the Write Tx Data block sample its input data? And if so, how should that sampling rate compare to the sampling rate of the input data?

Thank you for the assistance!

[wiebe@CARYA · Accepted solution]

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@krmills wrote:

This complex exponential is passed into the Write Tx Data block. My question becomes this: does the Write Tx Data block sample its input data? And if so, how should that sampling rate compare to the sampling rate of the input data?

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The two sine's are combined to form an IQ signal. Not sure where the term "complex exponential" comes from. 

The data is fed to the DDS at the programmed IQ rate. The DDS converts it up to the desired output frequency. Since your providing IQ data, the provided frequencies can be positive or negative. That's why the output frequency is the center, and you get your IQ data around that center.

So the data should be provided at the rate expected. If you make a 1 MHz sine, and you want the IQ rate to be 10 MHz, you need to create a 1MHz sine at 10 MHz. The output frequency is no factor in this.

Also see: Google How a DDS Works, What is IQ data and highly recommended I/Q Data for Dummies (because it's good, not calling you a dummy, I've read it).

[krmills]

Thank you for the response! That really helps clarify things for me.

To clarify something for you, by "complex exponential" I was referring  to Euler's formula. That is, exp(jx) = cos(x) + jsin(x).

[wiebe@CARYA]

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@krmills wrote:

Thank you for the response! That really helps clarify things for me.

To clarify something for you, by "complex exponential" I was referring  to Euler's formula. That is, exp(jx) = cos(x) + jsin(x).

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Ah, yes of course.  you're right, complex exponential like e(iwt) is a sine wave.