2.1 Amplitude modulation  (Page 3/4)

• Add the “Analog to Digital” and “Digital to Analog” converters (ADC and DAC) to your model:

• Add the multi-port selector, in order to split the stereo input.

• After placing the selector, double-click to open the dialog box and choose “columns” in the “select” label and “{1,2}” in the “indices to output label.

1. Configure the ADC and DAC blocks to a sampling rate to 96 KHZ and 16-bit samples.

• The final model should look as follows:

• You should configure the DSP constants as shown in Figure 28. The frame period for all constants should be -1

• Build the project and load the program to the DSK memory using ctrl+B.
• Make sure that the signals generator amplitude is set to 1 Volt and frequency of [0.1,5] kHz.
• Display the modulated and demodulated signals in the scope.

Model extensions

In this section we will extend the functionality of the example. Adding two more features:

• A variable frequency carrier generator (Please refer to secion "A Configurable Carrier Wave Generator" in the Appendix)
• An additional model for AM detection (Please refer to secion "The Coherent Detector (in brief)" in the Appendix).
• Build GUI that we will enable:
  • Changing the modulation index
  • Changing the carrier frequency
  • Selecting the detection scheme

The modulation index and carrier frequency will be changed through RTDX.

• Open the model created in the previous section
• Replace the constant modulation index by an RTDX input (Please refer to Figure 30), and name it InputModulation.

• Configure the RTDX input object to the values described bellow:

• Replace the sine wave block used for the carrier by the configurable carrier blocks (you may find them in the Configurable_Carrier.mdl file) The principle of operation of the Configurable Carrier Module is described in the Appendix. , and create a subsystem for the carrier generator as shown in Figure 32.

Your model should look as shown in Figure 33.

Figure 32 – Inserting a Configurable Carrier

• Enter the Configuration Parameters menu (ctrl+E). Choose Real-Time Workshop=>TIC6000 Code-Generator, In The Run-Time box change the Build Action to “Build” The models will be loaded by the GUI script. :

Push the OK button and close the “Configuration Parameters” window.

Rebuild *.out file using ctrl+B.

• Open the AM_Coherent.mdl file, and repeat step for this file.

You now have two load files each one corresponding to a different AM scheme.

Creating the gui

• Open a new GUI (Enter GUIDE in the MATLAB command line)
• Add 2 sliders and one list box to the GUI, so it would look like:

• Now, double click on the list-box and change the string field:

Change the string field to:

Coherent

SQRT

• In the Modulation index slider set: Min=0.75, Max=1.5.
• In the Carrier Frequency slider set: Min=1, Max=4.
• Press the “play” button so you can save your GUI and open the GUI script m-file.