PrinCom prefinals

Noise - is an electronic signal made up of many random frequencies at many amplitudes added to a radio or information signal when transmitted from one place to another or as it is processed.

interference - which disrupts a signal when unwanted signals are added.

signal noise - is unwanted interference that degrades a communication signal and affects both analog and digital signals,

There are two (2) classifications of noise, with each type of their own:

External Noise: This comes from sources that cannot be controlled by humans, such as in industrial, atmospheric, or space.

• Industrial Noise – produced by manufacturing equipment like automotive ignition systems, generators, and electric motors. Such electrical equipment that causes high voltages or currents to be switched creates transients, or momentary bursts of energy, that produce noise. Gas-filled lights, such as fluorescent lights, are also sources of industrial noise.

• Atmospheric Noise – electrical disturbances that happen naturally in the Earth’s atmosphere. This is also referred to as static, which usually comes from lightning. This type of noise also shows up as amplitude variations that add to a signal and interfere with it. Atmospheric noise also has the greatest impact on signals with frequencies below 30 MHz.

• Extraterrestrial Noise – in solar or cosmic, comes from space.

Solar noise - comes from the sun, which radiates a wide range of signals in a broad noise spectrum. The sun has a repeatable 11-year noise cycle where, at its peak, the sun produces an intense amount of noise that produces immense radio signal interference and makes many frequencies unusable for communication.

Cosmic noise - is generated by stars outside the solar system. Even though it does not produce impactful noise like the sun due to the stars’ distance from each other, it still shows up in the 10 MHz to 1.5 GHz range and causes great disruptions in the 15 − 150 MHz.

Internal Noise -This comes from electronic components in a receiver, such as resistors, diodes, and transistors. Internal noise is only low-level but often great enough to interfere with weak signals.

Common internal noise includes thermal noise, semiconductor noise, and intermodulation distortion.

• Thermal Noise – caused by thermal agitation, which is the random motion of free electrons in a conductor caused by heat. The movement of electrons starts a current flow that causes a small voltage to be produced across conductor components.

Electrons passing a conductor as current flows experience sudden obstacles in their path as they encounter thermally agitated atoms. The apparent resistance of the conductor thus changes, which creates thermal noise.

Thermal agitation is also referred to as white noise or Johnson noise after John Bertrand Johnson discovered it in 1928. White noise is believed to contain all frequencies randomly happening at random amplitudes based on the perception that white light has all other light frequencies. This will signify that a white noise signal occupies an infinite bandwidth. A filtered or band-limited noise, however, is called pink noise.

• Semiconductor Noise – comes from components such as diodes and transistors. Semiconductors

produce three (3) types of noise, including shot noise, transit-time noise, and flicker noise.

The current flow in any device is not direct and linear, which sometimes makes the current carriers, such as electrons, take random paths from source to destination. It is this random movement that produces the shot noise.

Transit time measures the period for the current carrier, such as an electron, to move from them input to the output. When the transit time of the signal frequency is the same as the time a current carrier takes to traverse from sender to receiver, a transit-time noise is created.

flicker noise - or excess noise comes from minute random variations of resistance in the semiconductor material. It is also referred to as 1/f noise as it is inversely proportional to frequency.

• Intermodulation Distortion – comes from generating new signals and harmonics caused by circuit nonlinearities since a circuit is never perfectly linear. This also occurs when two (2) or more signals are used in a non-linear circuit.

Signal-to-Noise Ratio (SNR) - This establishes the relative strengths of the signal and noise in communication systems.

Noise factor or noise ratio (NR) - is the ratio between S/N power at the input and S/N power at the output

Distortion - is a condition that adds unwanted change in the signal. It is the alteration of the waveform of an information signal of an audio or video signal in an electronic device or communication channel.

Dolby system - which is a noise reduction system, an audio signal is purposely distorted to emphasize aspects of the signal subject to electrical noise.

Selectivity - is the communication receiver’s ability to identify and select a desired signal from others present in the frequency spectrum.

LC-tuned circuits - (also called resonant circuits) made up of an inductor and a conductor.

ideal bandwidth (BW) - or the frequency range of the selectivity curve must be wide enough to pass the signal and its sidebands and narrow enough to eliminate or attenuate signals on adjacent frequencies.

shape factor - is used to express the steepness of the skirts.

Skirts, or skirt selectivity - are the sides of a tuned circuit response curve.

Sensitivity - This is mainly a function of overall gain, which is the factor wherein an input signal is multiplied to produce the output signal.

A method of expressing the sensitivity of a receiver is by obtaining the minimum discernible signal (MDS). It is the input signal level that is almost equal to the average noise floor of the receiver.

A noise floor - is the internally generated noise value.

Radio emission code designations - are assigned to many types of signals that can be used to interpret a detected signal easily.

The code is comprised of a capital letter, a number, and lowercase subscript letters. The capital letters are placed first and define the modulation type, the numbers are placed next and define the transmitted information type, and the lower subscript letters are used for more specific definitions and placed under the number.

ITU Emission Designation - is another system used to describe a signal but includes more variations. It is used by the standard organization International Telecommunication Union (ITU), which agreed on a set of codes to describe a format and modulation for a radio transmission easily.

Designators Format - This format allows anyone using the ITU system to quickly identify the parameters of a specific transmission.

Bandwidth Designator List - This has the format of three (3) digits that express the significant figures and a capital letter to express the decimal point