Continuous modulation of analog voltage output

[Natalie_H]

Hi,

I'm trying to generate a continuous high frequency (10-30kHz) analog voltage output from labview. I need to be able to modulate both the amplitude and frequency of the output whilst it is being sent out. Could anyone give me an indication of whether this is possible - both in terms of the high frequency nature of the signal and the continuous modulation of the signal.

Many thanks,

Natalie

[NIquist]

Modulation can be implemented in various ways.  High frequency is limited by the model of your DAQ card.

[Natalie_H]

Thanks for your reply. Could you possibly elaborate on the way in which voltage and freq can be modulated whilst the signal is being sent out. All the methods of modualtion I have seen allow you to set the parameters and then output the signal rather than allowing you to modulate the signal whilst it is being sent out

[NIquist]

Here is a good example of how to change DAQmx signal generation on the fly:  http://zone.ni.com/devzone/cda/epd/p/id/869

It's an old example using control polling rather than the event structure but it should get the point across.  Keep in mind that there are limitations to simple code.  If you need to guarantee that your waveform never glitches (no jumps) shen you change a parameter you have to code very specific timing into your VI and this can be tricky.

See if you can modify this achieve AM and FM.  Post your code if you get stuck.

[ashwini11]

Hello,

I am using DAQ to see the performance of analog modulation technique (PCB Board contianing modulator and demodualtor block). Here i am providing both my carrier and  message signal from arbitratry waveform generator of DAQ. I have attached obtained amplitude modulated waveform below. Within envelope my carrier should vary for modulation index=1 but here after the end point of msg envelope i am getting signals. I have repeated the same using normal oscilloscope.There i am getting proper output. Could you please suggest solution for this. 

[GeraldM]

Hey ashwini11,

I am somewhat unsure as to what your issue is but I was able to find a few resources that might be helpful for you! I have attached them below.

Simple AM Modulation in LabVIEW

https://forums.ni.com/t5/Example-Programs/Simple-AM-Modulation-in-LabVIEW/ta-p/3504360

Amplitude Modulation

http://www.ni.com/white-paper/3002/en/

How to perform AM-DSB Modulation/Demodulation using Modulation toolkit

https://forums.ni.com/t5/LabVIEW/How-to-perform-AM-DSB-Modulation-Demodulation-using-Modulation/td-p...

Also, the thread you are commenting on is kind of old. You might want to make a new forum post. This new post will have more exposure to active users of the forums, resulting in more people seeing your question and  potentially better conversation with other users.

[ashwini11]

Thank you so much sir. 

I would like to ask one more doubt regarding DAQ and NI elvismx instrument launcher. The oscilloscope and  Arbitrary generator from NI elvis will support a maximum sampling rate of 200kS/s. But in DAQ specification it is given that Analog input/output port supports a frequency range of 400kHz. How is this possible? Sampling rate should be greater than signal frequency. 

[GeraldM]

Hey ashwini11,

No problem. As I mentioned before this thread is old and your questions might not get much exposure. Also, since you are using NI-ELVIS I would suggest you post this second question on the NI-ELVIS forums instead of the LabVIEW forum. This will help you receive more targeted help from user who are more familiar with that product line.

NI ELVIS

https://forums.ni.com/t5/NI-ELVIS/bd-p/1022