Electromagnetic Waves, Signal Types, and Modulation Techniques in Communications

Ohm's Law (VIR)

relationship between voltage current and resistance example 12V and 4 ohm gives 3A

Direct Current (DC)

current flows in one direction example battery powering a flashlight

Alternating Current (AC)

current changes direction periodically example electricity from wall outlet

Impedance (Z)

total opposition to AC current including resistance and reactance example AC circuit with capacitor and resistor

Reactance (X)

opposition to AC caused by capacitors or inductors example capacitor blocks low frequency signals

Power (P)

rate of energy transfer measured in watts example 60W bulb uses more power than 10W bulb

Periodic signal

signal that repeats over time example sine wave or radio signal

Aperiodic signal

signal that does not repeat example human speech or noise

Amplitude

maximum strength of a signal example louder sound has higher amplitude

Period (T)

time for one complete cycle example one cycle in 0.01 seconds

Frequency (f)

number of cycles per second example 100 Hz means 100 cycles per second

Wavelength (λ)

distance traveled in one cycle example radio waves can be meters long

Electromagnetic wave (EM wave)

wave of electric and magnetic fields that carries energy example WiFi signal

Electric field (E field)

electric component of EM wave example force acting on charged particles

Magnetic field (H field)

magnetic component of EM wave example field around a current carrying wire