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IF phase bouncing when doing signal up-conversion

Hi, I have attached my project structure picture, it contains signal up and  down conversion.
TEM controller1.pngI use NI 5783 to generate two sinusoidal IF signals, IIF and QIF.

upconversion.JPG

Then I input this two signals into IQ modulator, and finding that when I update the IF signal, sometimes the RF signal's amplitude at fLO-fIF is strong, sometimes at fLO+fIF is strong. To find out the reason, I wired ni 5783 AO to AI directly. Using the Arctan function to do calculation on AI, it show that Arctan (I/Q) is bouncing 90 degree each time when I update the NI 5783 AO signal.

The way I create two quadrature signals is modifying the NI 5783 example, based on sine wave, I basically copy it and change the phase to be 90 degree lower to create a cosine signal.
screenshot.PNG

 

Hope I can get answers from you guys! 

 

Thank you 

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Message 1 of 3
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Maybe a race condition?

No need to use local variables. place them outside the case structure and wire them into both cases. Or rewire to just one case structure.

Next: Use the error wire and dataflow to make both configurations first and THEN the start.vis , same with the wait for transfer .....  

If you want to keep both error line seperate, use one case and sync with flat sequence..

Greetings from Germany
Henrik

LV since v3.1

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Message 2 of 3
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Thanks for replying!

I have tried your way but it does not work...

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