Wave Properties, Refraction, Modulation, and Radar Fundamentals (copy)

Amplitude

The height of the wave from the rest (equilibrium) position to the crest or trough.

Crest

The highest point of the wave above the rest position.

Cycle

One complete wave motion, typically measured from crest to crest or trough to trough.

Frequency

Number of waves.

Period

The time it takes for one complete cycle to pass a point.

Trough

The lowest point of the wave below the rest position.

Velocity

The speed at which the wave travels through a medium. Calculated as: velocity = frequency × wavelength.

Wavelength

The distance between two corresponding points on consecutive waves (e.g., crest to crest).

Refraction

The changing of direction of a wave as it leaves one medium and enters another medium of different density.

Reflection

The bouncing back of a wave when it strikes a surface that does not absorb the wave's energy.

Diffraction

The bending or spreading of waves around obstacles or through openings.

Multiplexing

A method for simultaneous transmission of two or more signals over a common carrier wave.

Bandwidth

The difference between the highest usable frequency of a device (upper frequency limit) and the lowest usable frequency of the device (lower frequency limit) measured at the half-power points.

Keying

Relays used in radio transmitter where the ordinary hand key cannot accommodate the pate current without excessive arcing.

Polarization

The orientation of the electric field of a wave relative to the Earth's surface.

Doppler Effect

The apparent change in frequency or pitch of a wave due to the relative motion between the source and the observer.

Ground Waves

Travel along the surface on the Earth and follow its curvature.

Sky Waves

Radiated upward and refracted back to earth by the ionosphere, allowing long-distance communication.

Space Waves

Travel directly from the transmitting antenna to the receiving antenna through the atmosphere.

Surface Waves

The component of ground waves that travels along the Earth's surface.

Skip Zone

A zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to Earth.

Troposphere

Sea level to 3.7 miles.

Stratosphere

3.7 miles to 250 miles.

Ionosphere

250 miles to space.

Weather

Affects radio waves primarily at frequencies above 100MHz. Rain, snow, fog, and humidity can cause scattering and absorption, leading to signal degradation.

Attenuation

The loss of signal strength as a wave travels through a medium.

Fading

The variation in signal strength due to changes in the transmission path.

Sunspots

Temporary phenomena on the Sun's surface that increase solar radiation.

Ducting

Trapping of an RF wave between two layers of the Earth's atmosphere or between an atmospheric layer and the Earth.

Ionization

Process where solar UV radiation energizes atmospheric particles, creating ions.

Solar flares

Intense bursts of radiation from the Sun.

Modulation

The ability to impress intelligence upon a transmission medium such as radio waves.

Demodulation

The removal of intelligence from a transmission medium.

USB (Upper Sideband)

When modulated by voice or music signals, all of the sum frequencies above that of the carrier.

LSB (Lower Sideband)

When modulated by voice or music signal, all difference frequencies below that of the carrier.

CW (Continuous Wave)

Modulation by on/off keying—Morse code. (Can also be Carrier Wave - which carries multiple frequencies over one channel.)

Phase

Angular position of the sine wave at a given moment of time.

AM (Amplitude Modulation)

Any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance with message intelligence.

FM (Frequency Modulation)

The variation of the instantaneous frequency of the carrier, either above or below the frequency.

SSB

Single Sideband is a refined form of amplitude modulation where only one sideband is transmitted.

Double Side Band

Form of amplitude modulation where both the upper and lower sidebands are transmitted.

Phase Modulation

Angle modulation in which the phase of the carrier is controlled by the modulating waveform.

Pulse Modulation

A form of modulation in which one of the characteristics of a pulse train is varied.

Angle Modulation

Modulation in which the angle of a sine-wave carrier is varied by a modulating wave.

Half Duplex

Provides communications in both directions, but only in one at a time.

Full Duplex

Provides communications in both directions simultaneously.

Simplex

Communication that occurs in one direction only.

Semi-Duplex

Similar to half duplex but typically implies automatic switching between transmit and receive modes.

Broadcast

Simplex communication where one station transmits to multiple receivers simultaneously.

PRI or PRT (Plan Position Indicator)

Is the most common radar display used for (Pulse Repetition Rate is same as PRF) in which range is indicated by the distance of a bright spot or blip from the center of the screen and the bearing is indicated by the radial angle of the spot.

PRF (Pulse Repetition Frequency)

The rate at which pulses are transmitted, given in hertz or pulses per second. Reciprocal of pulse - repetition time.

RF (Radio Frequency)

The modulated carrier wave from a transmitter.

BW (Beam Width)

Angular width of the beam's curvature.

CW (Curve Width)

The width of the pulse arc.

PW (Pulse Width)

The duration of the pulse.

Scan

Systematic movement of a radar beam to cover a definite pattern or area in space.

True Bearing

The angle between true north and a line pointed directly at the target.

Relative Bearing

The bearing angle to the radar target is measured from the centerline of your own ship or aircraft.

Azimuth Angle

Angular measurement in the horizontal plane in a clockwise direction.

Elevation Angle

Used by height finding radars, Uses a very narrow beam in both horizontal and vertical search planes.