Radio Wave Propagation

• Radio wave propagation concerns radiation and wave propagation

Radiation

• Radiation represents the loss or escape of energy into free space.

Wave Propagation

• Wave propagation constitutes the travel of electromagnetic waves through a medium.

Transverse Electromagnetic Waves

• Electromagnetic waves consist of radiant energy, including heat, light, radio, X-rays, and television waves.
• Electromagnetic waves are oscillatory disturbances in free space.

Characteristics of Electromagnetic Waves

• Wave velocity, frequency, wavelength, and polarization are characteristics of electromagnetic waves.

Nomenclature of Frequency Bands

• Very Low Frequency (VLF) waves range from 3–30 kHz, have a myriametric wave metric subdivision, and propagate as ground waves.
• Low Frequency (LF) waves range from 30-300 kHz, have a kilometric wave metric subdivision, and propagate as ground waves.
• Medium Frequency (MF) waves range from 300-3000 kHz, have a hectometric wave metric subdivision, and propagate as ground waves.
• High Frequency (HF) waves range from 3–30 MHz, have a decametric wave metric subdivision, and propagate as sky waves.
• Very High Frequency (VHF) waves range from 30–300 MHz, have a metric wave metric subdivision, and propagate as space waves.
• Ultrahigh Frequency (UHF) waves range from 300-3000 MHz, have a decimetric wave metric subdivision, and propagate as space waves.
• Superhigh Frequency (SHF) waves range from 3–30 GHz, have a centimetric wave metric subdivision, and propagate as space waves.
• Extremely High Frequency (EHF) waves range from 30–300 GHz, have a millimetric wave metric subdivision, and propagate as space waves.
• Decimillimetric waves range from 300-3000 GHz.

Frequency Spectrum

• Extremely Low Frequency (ELF) waves occupy the range of 30-300 Hz.
• Voice Frequency (VF) waves occupy the range of 300-3000 Hz.
• Very Low Frequency (VLF) waves occupy the range of 3-30 kHz.
• Low Frequency (LF) waves occupy the range of 30-300 kHz.
• Medium Frequency (MF) waves occupy the range of 300-3000 kHz.
• High Frequency (HF) waves occupy the range of 3-30 MHz.
• Very High Frequency (VHF) waves occupy the range of 30-300 MHz.
• Ultrahigh Frequency (UHF) waves occupy the range of 300-3000 MHz.
• Super High Frequency (SHF) waves occupy the range of 3-30 GHz.
• Extremely High Frequency (EHF) waves occupy the range of 30-300 GHz.

Mnemonics and Wave Metric Subdivision of the Frequency Spectrum

• VLF corresponds to "MY" and has a myriametric wave metric subdivision.
• LF corresponds to "KILI-KILI" and has a kilometric wave metric subdivision.
• MF corresponds to "HAS" and has a hectometric wave metric subdivision.
• HF corresponds to "THE" and has a decametric wave metric subdivision.
• VHF corresponds to "MOST" and has a metric wave metric subdivision.
• UHF corresponds to "DECENT" and has a decimetric wave metric subdivision.
• SHF corresponds to "C.." and has a centimetric wave metric subdivision.
• EHF corresponds to "..MELL" and has a millimetric wave metric subdivision.

Permeability

• Permeability measures a magnetic material's ability to concentrate magnetic flux.
• The permeability of free space ( 0) is approximately 4π x 10-7 H/m.

Permittivity

• Permittivity measures an insulator's ability to concentrate electric flux.
• The permittivity of free space (εo) is approximately (1 / 36π) x 10-9 F/m.

Free Space Characteristic Impedance

• Zo relates to the electric and magnetic field intensities of an electromagnetic wave in free space.
• The impedance of free space is calculated as Zo = √(μo / εo) = 377Ω.

Power Density

• Power density is the rate at which energy flows through a unit area of surface in space.
• Power Density is given by PD = EH (W/m^2) and also by PD = (E^2 / 377) = 377H^2 (W/m^2).

Spherical Wavefront

• A point source radiates power at a constant rate uniformly in all directions.
• A point source is also known as an isotropic radiator.
• Power density for a spherical wavefront is PD = Prad / (4πR^2).

Electric Field Intensity

• Electric field intensity is directly proportional to the square root of the power density and inversely proportional to the distance from the source.
• Electric field intensity is calculated as E = √(30Prad) / R, where E is in V/m, P is radiated power in watts, and R is the distance from the source in meters.

Attenuation

• Attenuation is the reduction of power density with distance from the source.
• Electromagnetic waves are attenuated as they travel outward and attenuation is proportional to the square of the distance traveled.
• Attenuation is calculated as α = 10 log (PD1 / PD2).

Absorption

• Some energy from electromagnetic waves is transferred to the atoms and molecules of the atmosphere, causing some radio waves to be absorbed.
• Absorption by the atmosphere depends on frequency.
• Absorption is insignificant below 10 GHz.

Refraction

• Refraction is the bending of a ray as it passes from one medium to another at an angle.
• Snell's Law is expressed as n1 sin θ1 = n2 sin θ2.
• The refractive index can be calculated as n = C / Vp and n = 1 / Vf and n = √εr.

Velocity Factor and Dielectric Constants in Various Materials

• Vacuum: Velocity Factor (k) is 1.0000 and Relative Dielectric Constant (εr) is 1.0000.
• Air: Velocity Factor (k) is 0.9997 and Relative Dielectric Constant (εr) is 1.0006.
• Teflon Foam: Velocity Factor (k) is 0.8200 and Relative Dielectric Constant (εr) is 1.4872.
• Teflon: Velocity Factor (k) is 0.6901 and Relative Dielectric Constant (εr) is 2.1000.
• Polyethylene: Velocity Factor (k) is 0.6637 and Relative Dielectric Constant (εr) is 2.2700.
• Paper (Paraffined): Velocity Factor (k) is 0.6325 and Relative Dielectric Constant (εr) is 2.5000.
• Polystyrene: Velocity Factor (k) is 0.6325 and Relative Dielectric Constant (εr) is 2.5000.
• Polyvinyl Chloride: Velocity Factor (k) is 0.5505 and Relative Dielectric Constant (εr) is 3.3000.
• Rubber: Velocity Factor (k) is 0.5774 and Relative Dielectric Constant (εr) is 3.0000.
• Mica: Velocity Factor (k) is 0.4472 and Relative Dielectric Constant (εr) is 5.0000.
• Glass: Velocity Factor (k) is 0.3651 and Relative Dielectric Constant (εr) is 7.5000.

Reflection

• Reflection involves the bouncing of electromagnetic waves off a smooth surface.
• The angle of incidence equals the angle of reflection.

Diffraction

• Diffraction is the redistribution (scattering) of energy within a wavefront when it passes near the edge of an object.

Huygen's Principle

• Every point on a given spherical wavefront may be regarded as a source of waves from which further waves are radiated outward.

Interference

• Interference occurs when two waves travel different paths from one source and arrive at a point.
• Interference can be constructive or destructive.

Ground Wave Propagation

• Ground wave propagation involves radio waves traveling or progressing along the surface of the Earth.
• Ground waves must be vertically polarized to prevent short-circuiting the electric component.

Advantages of Ground Wave Propagation

• Ground wave propagation can be used to communicate between any two locations in the world with enough power.
• Ground wave propagation is unaffected by changing atmospheric conditions.

Sky Wave Propagation

• Sky wave propagation involves radio waves radiated from the transmitting antenna at a large angle with reference to the Earth.

Atmospheric Layers

• The troposphere is the lowest layer of the atmosphere, where all weather disturbances take place, extending 8-10 miles above sea level.
• The stratosphere is directly above the troposphere and extends up to 40 miles above the troposphere, characterized by no weather but circulation.
• The ionosphere is the region in the atmosphere above the stratosphere, extending from 30-250 miles above the ground, where several ionized layers of low-density gas are found.

Ionospheric Layers

• The D layer is 50-100 km above ground, where atoms are broken into ions by sunlight and recombine quickly, disappearing at night and bending VLF and LF signals but not HF and MF waves.
• The E layer is 100-140 km above the ground, also known as the Kennelly-Heaviside Layer, disappears at night, aids MF surface wave propagation, reflects some HF waves in daytime, and where the Sporadic E layer appears.
• The Es layer/Sporadic thin layer of very high ionization density. Appears sometimes with the E layer and Often persists during the night
• The F layer Ions and electrons recombine more slowly. During the day, May split into two layers F1 and F2), combines during the night and is 180-400 Km above the ground
• The F1 layer exists at a height of 180 km in the daytime, combines with F2 at night, has a daytime thickness of about 20 km, and mainly provides absorption for HF waves.
• The F2 layer is the most important reflecting medium for HF radio waves, has an approximate thickness of 200 km, ranges from 250 to 400 km in daytime, and falls to approximately 300 km at night, combining with the F1 layer.

Ionospheric Propagation Parameters

• Critical frequency is the highest frequency at a given ionization density that is returned down to earth when beamed vertically upward.
• Critical angle is the highest angle of radiation that will return the wave to the earth at a given density of ionization for the specified layer, frequency, or wavelength.
• Maximum Usable Frequency (MUF) is the highest frequency that is returned to the earth at a given distance when beamed at a specific angle other than the normal, and is calculated as MUF = fc / cos θ.
• Optimum Working Frequency (OWF) is the frequency that provides the most consistent communication, thus this frequency is chosen to avoid irregularities of the atmosphere, and the formula is OWF = 0.85(MUF).
• Virtual height is the apparent height of the ionized layer, and it is measured by sending a wave vertically to the layer.

Skip Zone

• Skip zone is the area that lies between the outer limit of the ground-wave range and the inner edge of energy return from the ionosphere.

Skip Distance

• Skip distance is the distance between the originating site and the beginning of the ionospheric return.

Space Wave Propagation

• Space wave propagation involves radio waves that leave the transmitting antenna and travel in a straight line toward the receiving antenna.

• Space wave propagation is also known as line-of-sight propagation.

• Space wave propagation is best for VHF and UHF frequencies.

• Radio range is greater than the Optical range because the effect of the earth's atmosphere is to cause bending of the radio waves

• Radio horizon is calculated as dmi = √(2hT(ft)) + √(2hR(ft)) or dKm = √(17hT(m)) + √(17hR(m)).

Super Refraction/Ducting

• Super refraction/ducting occurs when a layer of cool air is trapped below a warmer air and can cover distances up to 1000 Km.