3d153v2 CDC Unit Review

Over-the-air rekeying (OTAR) is the common name for the method of changing encryption keys over the radio channel in a two-way radio system. This process allows for secure and efficient key management, ensuring that the encryption keys used for communication are regularly updated to maintain the security of the system. By changing the keys over the airwaves, the system can avoid the need for physical contact or manual intervention, making it a convenient and effective method for key management in radio communication.

A transceiver is a combination of a transmitter and receiver that is built as a single unit and shares common tuned circuits. This allows for the transmission and reception of signals using the same device, making it more compact and convenient. Transceivers are commonly used in various communication systems, such as radios, wireless networks, and telecommunications equipment.

The transceiver's computerized components and micro-circuitry can perform specific equipment faults, internal equipment tests, and internal calibrations. However, it cannot repair itself. This means that if the transceiver experiences any damage or malfunction, it would require external intervention or manual repair rather than being able to fix the issue on its own.

The Amazon jungle is the most challenging location for a radio frequency (RF) transmission systems technician to establish and operate a radio station from. This is because the dense vegetation and vast expanse of the jungle make it difficult for radio signals to penetrate and travel long distances. Additionally, the high humidity and constant rainfall in the region can interfere with the transmission and reception of radio waves. The presence of numerous obstacles such as trees and foliage further hinders the establishment of a reliable radio station in the Amazon jungle.

Frequencies higher than the critical frequency are passed into space. This is because the critical frequency is the maximum frequency that can be refracted back to Earth by the F2 layer of the atmosphere. Any frequencies higher than the critical frequency are not able to be refracted and therefore pass through the F2 layer and continue into space.

Sunspots are disturbances that occur on the sun's surface. These are dark spots that appear to be cooler than the surrounding areas, caused by intense magnetic activity. Sunspots are often associated with solar flares and other solar phenomena. They can vary in size and shape and are important for studying the sun's magnetic field and its effects on space weather. Therefore, the correct answer is "on the sun's surface."

The Federal Communications Commission (FCC) is the U.S. government agency responsible for dividing the radio frequency (RF) spectrum into different bands. The FCC regulates and licenses the use of the RF spectrum to ensure efficient and interference-free communication. They allocate specific frequency bands to different services such as television, radio, cellular communication, and wireless internet. This helps to prevent overlap and interference between different users and allows for the smooth operation of various wireless devices and services.

Decryption is the correct answer because it refers to the process of converting encrypted or scrambled information back into its original, intelligible form. Encryption is the process of converting information into a secret code, cryptography is the study and practice of secure communication, and crypto-analysis is the process of analyzing and breaking codes. Therefore, decryption is the specific process of reversing encryption and making the information readable again.

Ground waves are radio waves that travel near the Earth's surface. These waves are able to follow the curvature of the Earth and can travel over long distances. Ground waves are commonly used for broadcasting radio signals and are able to penetrate buildings and other obstacles. They are different from sky waves, which are radio waves that are reflected off the ionosphere and can travel much farther distances. Therefore, ground waves are the correct term for radio waves that travel near the Earth's surface.

The abbreviation FOT stands for "frequency of optimum transmission". This means that FOT refers to the frequency at which transmission is optimal or most efficient. It implies that there is a specific frequency at which data or signals can be transmitted with the least amount of interference or loss.

Electronic warfare (EW) refers to any military action that utilizes the electromagnetic (EM) spectrum, including directed energy, to attack an enemy. This can involve disrupting or disabling enemy communication systems, radar systems, or other electronic devices. Electronic support (ES) involves actions that provide electronic intelligence and support to EW operations. Electromagnetic pulse (EP) refers to a burst of electromagnetic energy that can disrupt or damage electronic systems. Electromagnetic interference (EI) refers to the unintentional disruption of electronic devices by electromagnetic radiation. Therefore, the correct answer is electronic warfare (EW).

Each word of day (WOD) in HAVEQUICK II communications can be used for a duration of 24 hours before it is manually changed.

Reciprocity refers to the ability of an antenna to both receive and transmit signals equally well. This means that the antenna's performance is the same regardless of whether it is used for receiving or transmitting. Reciprocity is an important characteristic of antennas as it allows for efficient and reliable communication. It ensures that the signals transmitted by the antenna are accurately received by the receiving device, and vice versa.

When a transmitted signal travels over two or more separate paths during transmission, it experiences multipathing. This phenomenon happens when the signal reflects, refracts, or diffracts off objects in its path, resulting in multiple copies of the signal reaching the receiver at slightly different times and angles. Multipathing can cause interference, signal fading, and distortion, affecting the quality and reliability of the transmitted signal.

A rigid coaxial cable is a transmission line that consists of a center conductor placed inside a metal tube functioning as the outer conductor. This design provides a high level of shielding and prevents interference from external sources. The rigid structure of the cable ensures that it maintains its shape and does not bend easily, making it suitable for applications where stability and durability are important.

A ground-reflected path undergoes a 180 degrees phase shift because when a signal reaches the ground, it reflects back towards the receiver. This reflection causes the signal to experience a phase shift of 180 degrees compared to the direct path. This phenomenon is commonly observed in radio wave propagation, where signals can bounce off the ground and create a ground-reflected path.

During winter, the air is colder and denser, which allows sound waves to travel further and with less absorption. This results in a wider range of critical frequencies being heard compared to other seasons. In contrast, during summer, the air is warmer and less dense, causing sound waves to be absorbed more quickly and limiting the range of critical frequencies that can be heard. Therefore, winter is the season with the wider range of critical frequencies and less absorption of all frequencies.

The usable frequency spectrum for communication purposes ranges from 3 hertz (Hz) to 300 gigahertz (GHz+). This means that frequencies within this range can be effectively used for transmitting and receiving signals for communication. Frequencies below 3 Hz or above 300 GHz may not be suitable or practical for communication purposes.

The Navy uses the Enhanced Position Location Reporting System (EPLRS) to locate and track amphibious assault craft. This system allows the Navy to effectively monitor the movement and position of these specialized watercraft, ensuring their safety and enabling efficient coordination during military operations. The Army, Marines, and Air Force do not typically operate amphibious assault craft, making the Navy the correct answer.

In a deployed environment, a common problem with a mass alert system is cleanliness. This refers to the system's ability to remain free from dirt, dust, debris, or any other contaminants that could potentially affect its performance. If the system is not properly maintained and cleaned regularly, it may lead to malfunctions or failures, compromising its reliability and effectiveness in delivering mass alerts to the intended recipients.

An omnidirectional antenna radiates radio energy in a circular pattern, meaning that it emits signals in all directions equally. This type of antenna is commonly used in situations where the signal needs to reach multiple locations or devices without the need for precise aiming or alignment. It is ideal for applications such as broadcast radio, Wi-Fi routers, and mobile communication towers, where a wide coverage area is desired.

In high frequency (HF) communications, your station's self address is user programmed into your system. This means that the address is manually set by the user in their system. It is not shared with other members, nor is it the address of an unprogrammed station. Additionally, it is not the same address as other stations in the net. Each station has its own unique self address that is programmed by the user into their system.

A parabolic satellite antenna is a common type of satellite antenna that uses a parabolic reflector to focus incoming radio waves onto a feed horn at its focal point. This design allows for high gain and directivity, making it ideal for long-range communication with satellites. The parabolic shape of the antenna helps to minimize signal loss and interference, resulting in a more efficient and reliable satellite communication.

The near-vertical incidence skywave antenna is more effective when there is a mountain between you and the distant end. This is because the near-vertical incidence skywave antenna is designed to transmit and receive signals that are reflected off the ionosphere at very steep angles. This allows the signals to bypass obstacles like mountains and reach the distant end more effectively compared to other types of antennas such as whip, dipole, or discone antennas.

The field strength of a radio wave decreases with distance from the source. In this case, the field strength at one mile is given as 100 microvolts per meter. Since the distance is doubled to two miles, the field strength would be halved. Therefore, the field strength at two miles would be 50 microvolts per meter.

The primary and remote annunciators in an intrusion detection system (IDS) must be capable of operating independently of one another. This means that each annunciator should be able to function and provide alerts or notifications without relying on the other. This is important for ensuring that the IDS remains functional even if one of the annunciators fails or is compromised. By operating independently, the system can continue to monitor and detect intrusions effectively, enhancing the overall security of the premises.

A biometric hand geometry unit (HGU) provides positive identification through measurement of a hand. (pg. 4-11)
The card reader PIN pad/prompt can be used at portals to read the 'encoded magnetic stripe' on badges. (pg. 4-10)

Biometrics - (noun) - the practice of digitally scanning the physiological or behavioural characteristics of individuals as a means of identification. (World English Dictionary)

The concept that alternating current (AC) changes in magnitude and reverses its direction during each cycle is what makes radio transmission possible. AC allows for the creation and propagation of electromagnetic waves, which are used in radio transmission. The changing magnitude and direction of AC current allows for the modulation of these electromagnetic waves, enabling the transmission of information through radio waves.

The effectiveness of an entire transmitting and receiving system largely depends on impedance matching. Impedance matching ensures that the impedance of the transmitting device matches the impedance of the receiving device, allowing for maximum power transfer and minimizing signal loss. If there is a mismatch in impedance, it can lead to reflections and a decrease in signal quality, affecting the overall performance of the system. Therefore, impedance matching is crucial for optimizing the efficiency and effectiveness of the system.

The correct answer is "optimizing the antenna's radiating pattern for its application." The location and orientation of an antenna on an aircraft are determined by the need to optimize its radiating pattern for its specific application. Different types of antennas may require different placement and orientation to ensure the best performance in terms of signal reception and transmission. Factors such as the aircraft's structure, interference from other systems, and the desired coverage area all play a role in determining the optimal location and orientation for an antenna.

Refraction is the correct answer because it is the bending of radio waves as they pass through different layers of the atmosphere. This bending allows the waves to follow the curvature of the Earth, enabling communication beyond the optical line-of-sight. Refraction is caused by the variation in the density of the atmosphere, which results in changes in the speed of the radio waves. This phenomenon is crucial for long-distance communication, as it allows signals to be transmitted over the horizon and reach receivers that are out of the direct line-of-sight.

The lowest usable frequency (LUF) refers to the lowest frequency that can be reliably received at a distant receiver on most undisturbed days of the month in high frequency (HF) communications. It represents the minimum frequency that can be used for effective communication without significant interference or signal degradation. The LUF is an important parameter to consider when determining the appropriate frequency for HF communication to ensure reliable transmission and reception.

Satellite communications were developed as a solution to overcome the limited range of forward propagation by tropospheric scatter (FPTS) without the need for costly relay systems. Unlike other options such as optical horizon radar, microwave communications, and line-of-sight (LOS) communications, satellite communications provide a reliable and efficient means of long-distance communication by using satellites to transmit and receive signals. This technology allows for global coverage and eliminates the need for physical infrastructure like relay systems, making it a cost-effective solution for overcoming the limitations of FPTS.

The correct answer is 20 Watts in AM, 50 Watts in FM. This means that the AN/GRC-171B(V)4 transceiver has an output power of 20 Watts when operating in amplitude modulation (AM) mode and 50 Watts when operating in frequency modulation (FM) mode.

AFI 10-2501 is the correct answer because it is the Air Force instruction that requires communications squadrons to maintain "installation warning systems". This instruction likely outlines the specific requirements and guidelines for maintaining these systems, ensuring that communications squadrons are able to effectively warn and communicate with personnel in the event of emergencies or other critical situations on the installation.

Fidelity refers to the ability of a receiver to reproduce the input signal accurately. It is a measure of how well the receiver can maintain the original quality and integrity of the signal without any distortion or loss of information. A receiver with high fidelity will accurately reproduce the original signal, while a receiver with low fidelity may introduce noise, distortion, or other errors that degrade the signal quality. Therefore, fidelity is the correct characteristic that describes the ability to reproduce the input signal accurately.

A nonresonant transmission line is a line that does not have any reflected waves. This means that all the energy transmitted through the line is absorbed and there are no waves bouncing back. This can be achieved by properly matching the impedance of the line with the load impedance. When there are no reflected waves, it indicates efficient power transfer and minimal signal loss along the transmission line.

The Earth has the greatest effect on an antenna because it is the largest and closest object to the antenna. The Earth's gravitational pull and electromagnetic field can interfere with the antenna's signal reception and transmission. Additionally, the Earth's atmosphere and terrain can also affect the antenna's performance by causing signal reflections, absorption, or blockage.

The MILSTAR satellite system uses super-high frequency (SHF) and extremely high frequency (EHF) bands. These frequency bands are commonly used for satellite communications due to their ability to transmit large amounts of data over long distances. SHF and EHF frequencies are also less susceptible to interference and can provide more secure and reliable communication channels.

The correct answer is the deliberate radiation of EM energy intended to convey misleading information to an enemy. Electromagnetic deception in electronic warfare involves intentionally emitting electromagnetic energy to deceive the enemy by conveying false or misleading information. This can be done by mimicking friendly signals, creating false targets, or distorting the enemy's perception of the battlefield. By using electromagnetic deception, military forces can confuse and mislead the enemy, potentially gaining a tactical advantage in combat operations.

In frequency hopping (FH) operation, the interval at which each transmitter remains on a given frequency for a specific time is known as the dwell time. This refers to the duration for which a transmitter stays on a particular frequency before switching to another. It is an essential parameter in FH systems as it determines how frequently the transmitter changes frequencies, and it affects the overall performance and efficiency of the system.

When a transmission line is terminated in a short, it means that the impedance at the termination is very low. In this case, the current flowing through the line will be at its maximum because the low impedance allows for a larger current to flow. On the other hand, the voltage at the termination will be at its minimum because a low impedance causes a drop in voltage. Therefore, the correct answer is that the current is at maximum and the voltage is at minimum at the termination.

The recombination process is dependent upon the time of day. This suggests that the process of recombination, which involves the rearrangement of genetic material, is influenced by the specific time of day. It implies that the timing of certain biological processes, such as DNA repair and replication, may play a crucial role in recombination. The answer choice "time of day" aligns with this understanding, indicating that the recombination process is influenced by the specific time within a day.

A speaker cell in a Whelen siren stack contains a 400-watt driver. This indicates that the speaker cell is designed to handle a power output of 400 watts, which suggests that it is capable of producing a loud and powerful sound. The higher wattage driver allows for a greater sound output, making it suitable for emergency vehicles or situations where a loud siren is necessary to alert others.

The correct answer is a transmitter. In the context of generating, amplifying, and transmitting RF carrier, the equipment responsible for performing these functions is known as a transmitter. A transmitter is used to convert information or signals into a form suitable for transmission over the airwaves. It generates the RF carrier signal, amplifies it to the desired power level, and transmits it through an antenna.

Reception is the correct answer because it refers to the basic receiver function of having the transmitted electromagnetic wave pass through the receive antenna and induce voltage in the antenna. This process allows the receiver to capture the signal and convert it into a usable form for further processing or analysis.

An antenna converts radio frequency (RF) energy's current oscillation into electric and magnetic fields of force. It is a device that radiates or receives electromagnetic waves. Antennas are used in communication systems to transmit or receive signals wirelessly. They convert the electrical current flowing through them into radio waves that can be transmitted through the air or other mediums.

Unidirectional antennas are usually used on long-range, point-to-point circuits where concentrated radio energy is needed for circuitry reliability. These antennas have a focused radiation pattern that allows them to transmit and receive signals in a specific direction, providing a stronger and more reliable signal over long distances. Unlike omnidirectional antennas that radiate energy in all directions, unidirectional antennas concentrate the radio energy in a single direction, making them ideal for long-range communication. Bidirectional antennas can transmit and receive signals in two opposite directions, while circular antennas are designed for circular polarization and are not specifically used for long-range, point-to-point circuits.

A helical antenna radiates a signal with circular polarization. This means that the electric field vector of the signal rotates in a circular motion as it propagates. Circular polarization allows the signal to maintain its polarization regardless of the orientation of the receiving antenna, making it more reliable in various applications.

The communications emphasis in the VHF/UHF frequency range is on air-ground comunications and short range point-to-point communications. (pg. 2-26)