Do you have an example of how to downcovert an output audio signal from a modem and then demodulate it in real time? I should plug the audio output from the modem into the audio input port of the computer sound card, right? And how do I tell Labview to read in from the input audio port?Also, I'm not sure how to enter some of the parameters in the digital demodulation toolkit. I also need to apply a Nyquist filter. Could you please provide me with an example? Here is an example of the modem spec:1200 baudscenter frequency at 1400hz, the pulse width is 1200hzHow would I input these information into the modulation toolkit? I'm using version 3.0 with labview 8.6 developer edition.thanks,

Hi Lavalava, Thanks for all of the detailed posts with information. With the help of my colleagues, I believe we have come up with the solution. You're absolutely correct in that the sampling rate was the problem. We were sampling such that we had 22,000 samples per second. The signal was generated at a very specific baud rate and symbol rate. At 2400 symbols per second and 16 samples per symbol, we can easily multiply the both to find that the signal is set at 38400 samples per second. Using this value, we can use the modulation toolkit vi (MT Fractional Resample.vi) to digitally resample the waveform at the appropriate 38400 samples per second. After resampling the waveform, we can appropriately filter, demodulate, and plot the constellation. All of this is demonstrated in the attached vi. At the end of the vi, you can also use the Truncate Filter Transient.vi to truncate the waveform based on the filter length and samples per symbol. Please open the attached example, set the appropriate baud rate on the front panel, and the vi should show you a clean constellation of the 22kHz wav file. I hope this helps,Paul C.

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modulation

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Re: modulation

lavalava

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‎11-12-2009 10:30 AM

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