IF phase bouncing when doing signal up-conversion

[zyb1003]

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

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.

Hope I can get answers from you guys! 

Thank you 

[Henrik_Volkers]

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..

[zyb1003]

Thanks for replying!

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