LabVIEW

cancel
Showing results for 
Search instead for 
Did you mean: 

Operation at high frequencies.

Solved!
Go to solution

This is rather a silly question. While generating a sinusoidal signal why the shape of the signal gets distorted when I increase the frequency? I am attaching snapshots.  I am using NI PXIe-6366 which has sampling rate 2 MS/s/ch. And I have kept sampling rate as 1Msps while generating the signal. 

The bigger problem that I am facing is that if I transmit this distorted signal, the received signal is even more distorted and I am unable to do the processing required. Its working fine for lower frequencies.

 

 

Download All
0 Kudos
Message 1 of 3
(2,060 Views)
Solution
Accepted by topic author maverikk

How well can you recreate the shape of a sine curve with 5, 4, or ~3 points?  Not very well, as you're seeing.   A typical rule of thumb I've followed is to try to have an output rate that's ~20x the sinusoid waveform frequency when possible.  Then each sine wave is defined with 20 points and starts to show a more realistic sinusoidal shape.  What you can "get away with" depends very much on the system receiving the signal you're generating.

 

When displaying an AO signal on a LV graph, I often right-click the plot in the graph legend and change the interpolation mode.  There's an option that will make the graph look a bit more like the actual D/A output signal -- it's an instant rise to the sample value followed by a flat hold until the next sample value.

 

 

-Kevin P

CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
Message 2 of 3
(2,051 Views)

 


@maverikk wrote:

This is rather a silly question. While generating a sinusoidal signal why the shape of the signal gets distorted when I increase the frequency?  


I know you are not doing audio but this Basics of Digital Audio site will help.

 

Specially page about Nyquist's Sampling Theorem.

========================
=== Engineer Ambiguously ===
========================
Message 3 of 3
(2,027 Views)