Baseband IQ to RF Signal Generation

Body:

I'm working on the IQmod example in MATLAB and attempting to generate a 4FSK signal for transmission at 150 MHz. However, I'm unclear about how to control the center frequency of the transmitted signal.

Current Approach:

• I've tried using the center frequency option in the inport block, but it doesn't seem to affect the transmission frequency.
• The iqmodulator block offers a local Oscillator option, but its purpose in setting the center frequency isn't entirely clear.

My Question:

• How can I properly set the center frequency to 150 MHz for transmitting the 4FSK signal using the IQmod example? Should I be modulating the baseband signal with a carrier at 150 MHz before feeding it to iqmodulator? Or is there another approach within the existing structure?

Additional Information:

• I'm using a sampling rate of 1 MHz for the IQ data.

Answer 1

[Uday]

Hi Dhruv,

The "iqmodulator" block handles baseband IQ modulation. To transmit your 4FSK signal at 150 MHz, you'll need to add a carrier outside the block.

Two options:

1. External Modulation: Modulate your 4FSK with a 150 MHz carrier (e.g., cos block) before feeding it to "iqmodulator".
2. Simulink Upconversion: Use Simulink's upconversion blocks to achieve the frequency shift.

Keep your 4FSK signal components below 500 kHz to avoid aliasing.

Refer: https://www.mathworks.com/help/simrf/ug/modulate-two-tone-dc-signal-using-idealized-baseband-mixer-block.html for more details.