Definition

• An electromagnetic wave is the propagation of an oscillating electric and magnetic field

• When the oscillation frequency is in the peta-hertz range we see this as light

• Sound waves in a gas or liquid are longitudinal waves and not transverse waves.

• Transverse waves oscillations are perpendicular to the direction of energy transfer and travel.

Fields

electromagnetic radiation involves both electric fields and magnetic fields and the changing of these

Waves

A changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This is known as an electromagnetic wave.

Some Math

Don’t groan

Inverse Square law

The energy decreases (divided by 4) as the distance r is doubled

If measured in dB would decrease by 3.01 dB per doubling of distance.

dB and dBi

• Gain is expressed in logarithmic units called decibels (dB).
• When gain is calculated with respect to an isotropic antenna, these are called decibels isotropic (dBi)

Isotropic Antenna

In reality, a coherent isotropic radiator of linear polarization can be shown to be impossible.

Path Loss

Path loss may be due to many effects

• free-space loss
• refraction
• diffraction
• reflection
• absorption

Path loss is also influenced by

• terrain contours
• environment (urban or rural, vegetation and foliage)
• propagation medium (dry or moist air)
• the distance between the transmitter and the receiver
• the height and location of antennas

Attenuation

The reduction in power density (attenuation) of an electromagnetic wave as it propagates through space

Refraction

The change in direction of a wave passing from one medium to another or from a gradual change in the medium.

Reflection

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

what these mean

• Frequency is the oscillation rate of the electric or magnetic field measured in Hertz and denoted as Hz
• Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. (usually measured in Hz)

Frequency Modulation

Frequency modulation changes frequency along the bandwidth to encode information

Frequency Modulation

Omni-Directional

Omni-Directional Purposes

Omni Directional are the most common

Omni-Directional Caveats

omni directional antennas might be broadcasting or receiving where you don’t want them due to placement

Directional (Yagi)

Directional (Yagi) Purposes

Yagi is for highly directional usage

Directional (Yagi) Caveats

directional antennas have side lobes and can broadcast or receive where you don’t want it