# Lecture Review: RF Waves

Disclaimer:

These lecture review posts are a personal study tool. Because they are written from memory (usually) to re-enforce what I’ve learned, often at a fast speed, these posts don’t represent my true formatting/writing skill.

These are electromagnetic waves. They contain a magnetic wave and an electric wave at 90 degree angles. They travel at speed of light and in all directions.

Several ways to describe waves:
1. Amplitude
2. Frequency
3. Wavelength
4. Phase (sorta)

Amplitude is the ‘height’ of the wave’s peaks.
Frequency is how many times a wave completes an up-and-down movement, returning to baseline, in a given amount of time.Wavelength is how long or short the waves are. Wavelength and amplitude have an inverse relationship.

Radio waves have to be ‘keyed’ or ‘modulated’ in order to carry data. A radio wave that has been keyed or modulated is called a carrier wave.

Radio waves can be analog or digital. Analog waves are continuous waves whereas digital waves can start and stop. Analog waves are modulated whereas digital waves are keyed.

Three modulations:
1. Phase Modulation
2. Amplitude Modulation
3. Frequency modulation

Phase Modulation changes starting point of waves where one position represents 1 and another represents 0.
Amplitude Modulation changes the height of the peaks where one height is 0 and another represents 1.
Frequency Modulation changes the wave’s frequency where a higher frequency represents 1 and a lower frequency represents 0.

FSPL stands for Free Space Path Loss. This is the natural attenuation (loss of signal) the radio wave naturally experiences as it travels.

Multipathing occurs when the same wave is bounced and reflected, creating copies, each reaching the receiver at the same time. This COULD be used to increase.

Rules of 10s and 3s.
-3dB means halve the watt value
+3dB means double the watt value-10dB means watt value becomes 1/10th of its value
+10dB means increase watt value by ten (multiply)

DON’T USE RSSI TO MEASURE SIGNAL STRENGTH!!!! It was never meant to do that! Only for internal use by the components. Further, each manufacturer can implement it differently.