Radio Transmitter Fundamentals and Wave Propagation

Vocabulary flashcards covering key terms and concepts from lecture notes on radio transmitter fundamentals and wave propagation.

Transmitter

Electronic unit that accepts the information signal to be transmitted and converts it into an RF signal capable of being transmitted over long distances.

Modulation

Process where the information signal modifies the carrier signal.

Crystal Oscillator

Oscillator capable of maintaining frequency precision and stability, often used as the source of carriers.

PLL Frequency Synthesizer

Used in applications requiring multiple channels of operation, providing an output that varies in fixed frequency increments.

DDS (Direct Digital Synthesis)

Generates a sine-wave output digitally, with the output frequency varied by a binary value.

Linear Amplifier

Amplifier that provides an output signal that is an identical, enlarged replica of the input.

Class A Amplifier

Amplifier biased so that it conducts continuously, producing an amplified linear reproduction of the input.

Class B Amplifier

Amplifier biased at cutoff, amplifying only one-half of the sine wave.

Class C Amplifier

Amplifier that conducts for less than one-half of the sine wave input cycle, known for its efficiency, often used for frequency multiplication.

Neutralization

Process where a signal equal in amplitude and 180° out of phase is fed back to cancel unwanted oscillations.

Impedance-Matching Network

Circuits used to connect one stage to another, providing optimum power transfer through impedance matching techniques.

Balun

Transformer used to connect a balanced source to an unbalanced load or vice versa.

Toroid

Circular, doughnut-shaped core, usually made of powdered iron, used in RF transformers to contain the magnetic field.

Radio Propagation

The propagation of electromagnetic waves through space.

Polarization

Orientation of the electric field vector in respect to the surface of the Earth.

Refraction

Bending of a radio wave path as it passes obliquely from one medium into another.

Diffraction

Modulation or redistribution of energy within a wavefront when it passes near the edge of an opaque object.

Interference

Occurs when two or more electromagnetic waves combine in such a way that the system performance is degraded.

Ground-Wave Propagation

Vertically polarized waves that follow the surface of the earth, typically using frequencies up to 2 MHz.

Ionospheric Propagation

Electromagnetic waves directed above the horizon and reflected or refracted back to earth by the ionosphere.

MUF (Maximum Usable Frequency)

Highest frequency that can be used for sky wave propagation between two specific points on Earth's surface.

Skip Distance

Minimum distance from a transmit antenna that a sky wave at a given frequency will be returned to Earth.

Space-Wave Propagation

Electromagnetic energy radiated or traveling in the troposphere, including direct and reflected waves.

Radio Horizon

Locus of points on the Earth's surface where rays from a transmitting antenna are tangent to the surface.

Duct Propagation

Occurs when electromagnetic waves are trapped between the lower atmosphere and Earth’s surface.

Multipath Propagation

A reduction in signal strength due to multipath propagation or reception

Free-Space Path Loss

Loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum.

Repeater

Transmits and receives simultaneously on at least two frequencies