AM demodulation in NI PXIe 5641r

[Ganesh20]

Hi

    I am doing demodulation in NI PXIe 5641r using Labview 2009 DS1.

    After demodulation i am trying to put Bandpass filter.

    In this while specifying lower cut off frequency and higher cutoff frequency i am getting error like your frequency should be withing 0<L_freq<=H_freq<=fs/2

    I tried with all the frequency but i am getting the same error.

    Please help me to rectify this....

    I have attached my block diagram of this

Thank You

[sahil_ni]

Hello,

The problem lies in the build waveform function.

The dt input that we specify in the build waveform function is basically the time in seconds between two samples. This can be correlated to the sampling frequency.So according to this value you should set the values in the bandpass filter.

If you want the high cutoff frequency at 500 Hz, your minimum sampling frequency should be 1000 Hz, which means that the time between two samples is 0.001 s. So set this value as dt in your build waveform function and it should work.

I think this should solve your problem.

Have a good day!!!!

[Ganesh20]

 Thank you sahil_ni.

 My ADC will produce I/Q data rate at 100MS/s. So i think, i need to give decimation divide by 100M to dt of build waveform vi.

 To my Bandpass filter i am able to give cutoff frequency less than 0.5 only. I think it is reading 1 samples only from FIFO and it is considering fs as 1 for each while loop

 I have difficulty in changing this so that i can limit my frequency within audio range (20Hz to 20KHz).