Learn LabVIEW DSP in 3 Hours - Challenge: AM Radio

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Using the LabVIEW Project with LabView DSP Module

 

AM radio is radio broadcasting using Amplitude Modulation. AM is a form of modulation in which the amplitude of the carrier wave is varied in direct proportion to that of a modulating signal. It was the first method used to broadcast commercial radio.

Using two NI SPEEDY-33 boards, develop an AM Radio application, where

• AM Transmitter VI modulates the input music signal and transmits it to the speakers acting as an antenna (first NI SPEEDY-33),
• AM Receiver VI receives the “broadcasted” signal (by AM Transmitter VI) over the air through the on-board microphones, demodulates the signal and outputs it to the headphones (second NI SPEEDY-33)

Note that you can substitute TI DSK6711 or DSK6713 boards for NI SPEEDY-33.


Hints

AM Transmitter (first board):

The following figure shows a high level diagram of a basic AM transmitter.

1. Obtain the music signal played on your computer and scale the signal down in case the music is too loud. You can also apply a Bandpass filter (with low and high cutoff frequencies of about 1 and 2kHz, respectively) before scaling the signal.
2. Multiply the signal by a high frequency carrier signal (i.e., a high frequency sine wave).
3. Generate a sweeping sine waveform and multiply it by another high frequency carrier signal.
4. Add the resulting signals from steps 2 and 3. Apply a Highpass filter with cutoff frequency of around 8000Hz.
5. Output the signal to the speaker. You should hear a high pitch noise coming from the speaker, since the music signal has been shifted to higher frequency.

AM Receiver (second board):

1. Obtain the signal transmitted through the air, scale it down and apply a Highpass filter with a cutoff frequency you have specified in step 4 above.
2. Multiply the signal by a high frequency carrier signal (the frequency you have used in step 2 above).
3. Apply a Lowpass filter with cutoff frequency around 1kHz and listen to the demodulated signal through the headphones.

The solution VIs for this challenge exercise are provided in the AM Transmitter and Receiver example program

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