113 EIWS COMM CORE (Technical Fundamentals)
Terms in this set (9)
113.1 Define each band of the electromagnetic spectrum and describe what signals are commonly used in each
Radio frequency: Used for transmission of data, via modulation. The frequencies falling between 3000 hertz (3 kHz) and 300,000,000,000 hertz (300 GHz) are called Radio Frequencies since they are commonly used in radio communications.
Microwaves: Used to heat food. Low-intensity microwave radiation is used in Wi-Fi, although this is at intensity levels unable to cause thermal heating.
Terahertz radiation: Terahertz radiation is a region of the spectrum between far infrared and microwaves. Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band, but applications such as imaging and communications are now appearing. Scientists are also looking to apply terahertz technology in the armed forces, where high frequency waves might be directed at enemy troops to incapacitate their electronic equipment.
Infrared radiation: Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm). This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in the Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere effectively opaque. However, there are certain wavelength ranges ("windows") within the opaque range which allow partial transmission, and can be used for astronomy. Near-infrared, from 120 to 400 THz (2,500 to 750 nm). Physical processes that are relevant for this range are similar to those for visible light.
Visible radiation (light): At most wavelengths, however, the information carried by electromagnetic radiation is not directly detected by human senses. Natural sources produce EM radiation across the spectrum, and our technology can also manipulate a broad range of wavelengths. Optical fiber transmits light which, although not suitable for direct viewing, can carry data that can be translated into sound or an image. The coding used in such data is similar to that used with radio waves
Ultraviolet light: Being very energetic, UV can break chemical bonds, making molecules unusually reactive or ionizing them, in general changing their mutual behavior. Sunburn, for example, is caused by the disruptive effects of UV radiation on skin cells, which is the main cause of skin cancer, if the radiation irreparably damages the complex DNA molecules in the cells.
X-rays: Hard X-rays have shorter wavelengths than soft X-rays. As they can pass through most substances, X-rays can be used to 'see through' objects, most notably diagnostic X-ray images in medicine, as well as for highenergy physics and astronomy.
Gamma rays: They are useful to astronomers in the study of high energy objects or regions, and find a use with physicists thanks to their penetrative ability and their production from radioisotopes. Gamma rays are also used for the irradiation of food and seed for sterilization, and in medicine they are used in radiation cancer therapy and some kinds of diagnostic imaging such as PET scans. The wavelength of gamma rays can be measured with high accuracy by means of Compton scattering
113.2 Describe the communication capabilities of transmissions in each of the bands below
a. EHF: Extremely High Frequency- 30GHZ to 300GHZ- Still in the experimental stages.
b. SHF: Super High Frequency- 3GHZ to 30GHZ- Used for satellite communication and radar.
c. UHF: Ultra High Frequency- 300MHZ to 3 GHZ- Also Line of sight.
d. VHF: Very High Frequency- 30MHZ to 300MHZ- Line of sight frequency, Hand held communications.
e. HF: High Frequency- 3MHZ to 30MHZ- Long range transmission of this signal is highly varied due to temperature and atmospheric conditions.
f. MF: Medium Frequency- 300KHZ to 3MHZ- The international distress frequency.
g. LF: Low Frequency- 30KHZ to 300KHZ- Expensive and bulky radio signal that is not widely used.
h. VLF: Very Low Frequency- 3 KHZ to 30KHZ- The most widely used signal for communications around the world. Used for fleet transmissions and navigation.
i. Voice Frequency (ULF): 300 HZ to 3 KHZ- Exactly what it sounds like
j. ELF: Extremely Low Frequency- 300 HZ and above- One way communications to Subs. This frequency is able to penetrate ocean depths.
113.3 Define and discuss the following terms
a. Frequency [ref. b]: Measured in Hertz (Hz), defines the number of cycles per second
b. Wavelength [ref. b]: The distance in space occupied by one cycle of a radio wave at any given instant
c. Ducting [ref. b]: Trapping of an RF wave between two layers of the earth's atmosphere or between an atmospheric layer and the earth
d. Refraction [ref. b]: When a wave passes from one medium into another medium that has a different velocity of propagation, a change in the direction of the wave will occur
e. Multiplexing [ref. a]: Method for simultaneous transmission of two or more signals over a common carrier wave
f. Modulation/Demodulation [ref. c]: Modulation is the process of transmitting impressed intelligence in the form of RF energy (transmitting) and demodulation is the process of removing the intelligence and back to its original state (receiving)
g. Bandwidth [ref. c]: The difference between the highest usable frequency of a device (upper frequency limit) and the lowest usable frequency of the device (lower frequency limit)
h. Keying [ref. c]: Initiates the process of transmitting by Morse, PTT, etc.
i. Azimuth Angle [ref. f]: The 360 degree angle at which the radio wave travels. Can have some effect on the angle of incidence at which a radio wave intersects the atmosphere layers.
j. Elevation Angle [ref. f]: The angle at which the radio wave travels from the antenna to the atmosphere. This affects the angle of incidence at which a radio wave intersects the atmosphere layers.
113.4 Discuss the following terms and give a description of what each means in relation to the atmosphere
a. Layers: The 3 main layers of the atmosphere are the troposphere, stratosphere, and ionosphere.
b. Frequency: The frequency of a radio wave plays a part in determining the atmospheric influence and radio wave. Depending on the layer of atmosphere, the frequency and angle of incidence of the radio wave, a transmitted radio wave can be reflected or refracted.
c. Radio Waves: Can be effected by various factors in the atmosphere including geographical location, sun activity, height within the atmosphere, and time of day.
d. Propagation Paths: Within the atmosphere, radio waves can be reflected, refracted, and diffracted like light and heat waves.
113.5 Describe the following modulation types and their common u
a. USB: (Upper Side Band) All sum frequencies above the carrier frequency. Requires less power for communications.
b. LSB: (Lower Side Band) All difference frequencies below the carrier frequency. Requires less power for communications
c. CW: (Carrier Wave) Contains center frequency of transmitted signal Largest part of the signal
d. AM: (Amplitude Modulation) Signal varies in amplitude but the radio-frequency wave is kept constant
e. FM: (Frequency Modulation) Signal varies in frequency but the amplitude remains constant
113.6 Define the following terms as they apply to RADAR
a. PRI: (Pulse Repetition Interval) time from the start of one radar pulse to the start of the next pulse, used in the determination of the range to target/return.
b. PRF: (Pulse Repetition Frequency) equal to the number of pulses emitted in one second.
c. RF: (Radio Frequency) energy is transmitted to and reflects from the reflecting job.
d. BW: (Bandwidth) refers to the frequency range of the transmitter and receiver of radar systems.
e. CW: (Continuous Wave) When radio-frequency transmitted from a fixed point continuously strikes an object that is either moving toward or away for the source of the energy, the frequency of the reflected energy is changed. Shift is known as Doppler Effect.
f. PW: (Pulse Width) the period of time during which the radar is actively transmitting a pulse of radio frequency.
g. Scan: The systematic movement of a radar beam in a definite pattern while searching for or tracking a target.
h. Bearing/Azimuth/Elevation: Relative bearing is the angle measured clockwise from the direction the ship is traveling, assigning the direction of the ship as 0 degrees. Azimuth (true bearing) is the angle measured clockwise from true north in the horizontal plane. Elevation is the angle on the vertical plane from the horizontal plane of the transmitter to the target.
113.7 Identify the following types of RADAR, their functions, and give examples of each
a. Air Search: Systems initially detect and determine the position, course, and speed of air targets in a relatively large area. (EX: SPS-49, SPY-1)
b. Surface Search: System has two primary functions (1) the detection and determination of accurate ranges and bearing of surface objects and low flying aircraft and (2) the maintenance of a 360-degree search pattern for all objects within line-of-sight distance from the radar antenna. (EX: SPS-67, SPS-73)
c. Fire Control: System usually produces a very narrow, circular beam. This type of radar is very accurate and is used to constantly track the position of a target for the development of a fire-control solution. (EX: SPQ-9, SPG62)
113.8 Explain the difference between OPELINT and TECHELINT
OPELINT: category of electronic intelligence concerned with the introduction, disposition, location, movement, employment, tactics, and activity levels of known foreign non-communications emitters and the weapon systems and associated.
TECHELINT: Category of electronic intelligence concerned with the signal characteristics, modes, functions, associations, capabilities, limitations, vulnerabilities, and technology levels of foreign non-communications emitters and the electronics or weapons systems with which they are associated.
113.9 Define the following
a. Half Duplex: Two way communication that is NOT simultaneous such as walkie talkie communication
b. Duplex: Two way simultaneous communication such as talking on a telephone.
c. Simplex: One way communication such as a radio transmission that is picked up by an FM receiver