Issues with AM Modulation Using NI 9263 and NI 9239 Modules

[matin.khalili68@gmail.com]

Hello everyone,

I am utilizing an NI 9263 analog output to generate a sine voltage with a frequency of 1 kHz and a peak voltage of 10 V. The intention is to use this signal as a carrier in a system for amplitude modulation (AM). The message signal is in the millivolt range, and I am acquiring data with an NI 9239 analog input. Both of these modules are integrated into an NI cDAQ-9178 system.

To test the input and output modules, I generate a 1 kHz sine voltage using the NI 9263 and directly connect it to the NI 9239 module. In this scenario, the output appears somewhat altered, as evidenced by the change in the envelope color in the first figure. I have employed an envelope function to illustrate the peak of this signal in the second figure. The amplitude is observed to fluctuate with a constant frequency between 9.89 V and 9.97 V. While this may be acceptable for general purposes, it becomes problematic for my application, where I intend to perform AM demodulation, and my message signal is in the millivolt range. The observed shape could potentially overlap with the message frequency.

To investigate whether the issue lies with the analog input or analog output, I checked an arbitrary waveform generator and found similar problems, indicating that the issue may be associated with the analog input. Do you have insights into what the problem might be and how I can address it?

Thank you

[santo_13]

Have you taken into account the resolution and accuracy specs of your modules to see if this is feasible?