Basic Radio Theory and Wave Propagation

This set covers fundamental vocabulary for radio theory, including electromagnetic wave properties, frequency bands, modulation types, and propagation characteristics based on the provided lecture notes.

Electromagnetic Wave

A wave of energy created by the simultaneous variation of electric and magnetic fields that propagates through space.

Cycle

A single oscillation of alternating current that travels from a positive phase to a negative phase and returns to positive.

Frequency ($f$)

The total number of cycles or oscillations that occur in one second, expressed in Hertz ($Hz$).

Wavelength ($\lambda$)

The physical distance a radio wave travels during the completion of a single oscillation cycle.

Speed of Light ($c$)

The constant speed at which electromagnetic waves radiate, approximately equal to $300,000,000\,m/s$.

Phase

A specific point in time within a waveform cycle, typically measured in degrees from $0^\circ$ to $360^\circ$.

Phase Difference

The angular or temporal difference between two waves of the same frequency, which is use as the operating principle for VOR navigation aids.

Amplitude

The measurement of the maximum displacement or strength of an oscillation relative to its mean position.

Radio Frequencies

Electromagnetic waves within the range of $300\,kHz$ to $300\,GHz$ used for radar and communication.

Beat Frequency Oscillator (BFO)

A device used in a receiver to make non-audible signals audible to humans, particularly used with single sideband transmissions.

Carrier Wave (CW)

A high-frequency electromagnetic wave used to transport signal information through modulation.

Modulation

The process of altering the characteristics of a carrier wave, such as its amplitude or frequency, to convey information.

Amplitude Modulation (AM)

A modulation technique where the strength of the carrier wave is varied while the frequency remains constant.

Frequency Modulation (FM)

A modulation technique where the frequency of the carrier wave is varied while the amplitude remains constant.

Demodulation

The receiver process of extracting the original audio frequency information from the carrier wave.

Polarisation

The orientation of the electric field of an electromagnetic wave, which can be vertical, horizontal, or cross-polarised.

Polar Diagram

A graphical representation used to show the relative strength and power of the field radiated by an antenna.

Half-wave Dipole

An antenna consisting of two conductive rods, with a total length equal to half of the signal's wavelength ($\frac{1}{2}\,\lambda$).

Unipole

A singular rod antenna mounted perpendicular to a conductive surface, often using an aircraft's fuselage to act as a ground plane.

Ground Waves

Radio waves that travel along the earth's surface and can bend over obstacles through a process called diffraction.

Diffraction

The phenomenon where radio waves bend around physical obstacles, which is more pronounced at lower frequencies.

Space Wave

A type of propagation where radio waves travel directly from transmitter to receiver or via surface reflection, often limited by line-of-sight.

Sky Waves

Radio waves that are reflected or refracted by the ionosphere, allowing for long-distance communication primarily in the HF band.

Skip Distance

The total distance measured along the earth's surface from the transmitter to where a sky wave returns after ionospheric reflection.

Dead Space

The region between the end of a ground wave's range and the first return point of a sky wave where no signal reception is possible.

Fading

The variation in signal strength caused by two or more waves arriving at a receiver at the same time either in phase or out of phase.

Attenuation

The gradual reduction in signal strength as a wave propagates through the atmosphere or over various surfaces.