Link to this headingIQ Signals

https://witestlab.poly.edu/blog/capture-and-decode-fm-radio/

Link to this headingInto

A: Amplitude
f: Frequency
phi: Phase

I: Amplitude of the cos wave
Q: Amplitude of the sin wave

v(t) = A * \sin(2 \pi * f * t + \phi)

v(t) = I * \cos(2 \pi * f * t + \phi)

x(t) = Q * \sin(2 \pi * f * t + \phi)

g(t) = v(t) + x(t)

By just varying I and Q you can make complex modulations to the phase and amplitude.

I and Q are used to remove the phase shift of a signal and use it as parts of the Amplitude of the signal. So by just using I and Q you can combine the two signals to generate a shifted signal


Plotting the values:


    

  • The amplitude of the signal is the hypotenuse.
    • 

  • The I value is the x value on the circle
    • 

  • The Q value is the y value on the circle
    • 

  • The phi is the angle the amplitude is at
    • 



Using the I and Q of an RF signal you can figure out the modulation of the signal


Link to this headingTypes of Modulation


RF parameters that can be modulated:


    

  • Amplitude (ASK)

      

    • Example lower amplitude could be a 0 and a higher amplitude could be a 1
      • 

    

    • 

  • Frequency (FSK)

      

    • Example lower frequency could be a 0 and a higher frequency could be a 1
      • 

    

    • 

  • Phase (PSK)

      

    • In phase could be a 0 and reverse phase could be a 1
      • 

    

    • 



Symbol: discrete state representing some quantity of information


Fast Fourier Transform: Decomposes a signal in to its component frequencies. Any Periodic signal can be modeled as the sum of harmonic sine waves


Link to this headingASK


OOK: Simple Amplitude modulation where the amplitude is either high or low.


Link to this headingFSK


GFSK: Gaussian Frequency Shift Keying passed through a Gaussian filter before modulation

BFSK:

2FSK: There are two frequencies one that represents a 1 and one that represents a 0


Link to this headingBinary Phase Shift Keying (BPSK)


    

  • I(t) is set to +1 or -1
    • 

  • Q(t) = 0
    • 



This gets one bit of information.


Link to this headingQuadrature Phase Shift Keying (QPSK)


    

  • I(t) is set to +1 or -1
    • 

  • Q(t) is set to +1 or -1
    • 



This gets two bit of information. Or 4 distinct states. 00, 01, 10, 11


Link to this headingAdvanced


With this type of modulation you can have more states for each I and Q.

This increases the bandwidth but does not work well with noise


Link to this headingAM Modulation


The I and Q are both moving up and down in amplitude


Link to this headingFM Modulation


The I and Q are rotating around the circumference of the circle both clockwise and counterclockwise