Z3D153 - 2016 Edit Code 3, Volume 2 Part 1

Radio waves that travel near the Earth's surface are called ground waves because they propagate by hugging the Earth's surface and following its curvature. These waves are able to travel over long distances and can be received by antennas located on the ground. Ground waves are commonly used for broadcasting and communication purposes, as they can easily penetrate buildings and other obstacles, allowing for reliable signal transmission.

High frequency (HF) is the correct answer because it is more susceptible to jamming compared to other frequency bands. HF signals have longer wavelengths and are more easily absorbed or reflected by the Earth's atmosphere, buildings, and other obstacles. This makes HF signals weaker and more prone to interference or disruption caused by intentional or unintentional jamming. Additionally, HF signals can travel long distances, making them attractive targets for jamming attempts by adversaries or interfering signals from other sources.

A combination transmitter and receiver, built as a single unit and sharing common tuned circuits, is called a transceiver. This device is capable of both transmitting and receiving signals, making it versatile and efficient. By combining these functions into one unit, it reduces the need for separate equipment and simplifies the overall communication system.

A transmission line that consists of a center conductor, placed inside a rigid metal tube that functions as the outer shield, is called a rigid coaxial cable. This type of coaxial cable provides better shielding and protection against interference, making it suitable for applications where signal integrity is crucial. The rigid nature of the metal tube provides stability and durability to the cable, making it less prone to damage.

The Federal Communications Commission (FCC) is the correct answer because it is the US government agency responsible for dividing the radio frequency spectrum into different bands. The FCC regulates and licenses the use of radio frequencies to ensure efficient and interference-free communication. They allocate different frequency bands for various purposes, such as television broadcasting, mobile communications, and emergency services. By managing the spectrum, the FCC ensures that different users can coexist and operate without causing interference to each other.

When a transmission line is terminated in an open, it means that the line is not connected to any load or device at the end. In this scenario, the signal traveling through the transmission line encounters a high impedance at the termination point, causing a significant reflection of the signal back towards the source. This reflection can lead to signal loss and degradation, resulting in a significant decrease in the strength and quality of the transmitted signal. Therefore, the correct answer is that signal loss would be significant.

The ability of a receiver to reproduce the signal of a very weak station refers to the receiver's sensitivity. Sensitivity is a measure of how well a receiver can detect and amplify weak signals. A receiver with high sensitivity will be able to pick up and reproduce signals from distant or weak stations, while a receiver with low sensitivity will struggle to do so. Therefore, sensitivity is the characteristic that determines the receiver's ability to reproduce weak signals.

High-frequency (HF) transmissions are normally conducted in single sideband (SSB) and independent sidebands (ISB) operating modes. SSB is a modulation technique that suppresses the carrier and one of the sidebands, resulting in more efficient use of bandwidth. ISB, on the other hand, allows for the transmission of multiple independent signals simultaneously by dividing the available frequency spectrum into separate sidebands. These two operating modes are commonly used in HF transmissions to maximize spectral efficiency and enable the transmission of multiple signals over long distances.

Fidelity refers to the ability of a receiver to accurately reproduce the input signal. It measures how well the receiver can maintain the original quality and integrity of the signal without any distortion or loss. Capacity refers to the amount of information a receiver can handle, sensitivity refers to the ability to detect weak signals, and selectivity refers to the ability to separate desired signals from unwanted interference. None of these options directly relate to accurately reproducing the input signal, making fidelity the correct answer.

A nonresonant transmission line refers to a transmission line where there are no reflected waves. Reflected waves occur when there is a mismatch between the impedance of the transmission line and the load impedance. In a nonresonant transmission line, the impedance is matched, resulting in no reflections. This means that all the energy is transmitted through the line without any portion being reflected back. Therefore, the correct answer is no reflected waves.

A waveguide is a type of transmission line that is used when the frequencies of the signals being transmitted are very high, resulting in very short wavelengths. Waveguides are designed to efficiently guide and transmit these high-frequency signals without significant loss or interference. The small size of the wavelengths makes it impractical to use other types of transmission lines, such as coaxial cables, which are more suitable for lower frequencies. Therefore, a waveguide is the appropriate choice when the frequencies are so high that their wavelength is miniscule.

The resistance of the conductor material in a transmission line causes loss of energy, known as conductor resistance loss. Copper is a commonly used conductor material in transmission lines due to its low resistance, which helps to minimize these losses. Copper's low resistance allows for efficient transmission of electrical energy, reducing the amount of power lost as heat in the transmission process.

Waveguides are structures that are designed to guide and transmit electromagnetic waves. The given answer states that "their outer surface will arc from being very slightly damaged." This statement is incorrect because waveguides are typically made of conductive materials that can withstand slight damage without arcing. Arcing occurs when there is a high voltage breakdown across a gap, and it is not a characteristic of waveguides. Therefore, this statement does not hold true for waveguides.

Direct waves are radio waves that travel through the air in a straight line from the transmitter to the receiver. Unlike other types of waves, direct waves do not bounce off or get interrupted by obstacles in their path. This allows them to travel long distances without significant interruptions. The statement about direct waves traveling no more than 20 miles to the receive antenna is incorrect, as direct waves can travel much farther depending on the power of the transmitter and other factors.

Leakage loss in a transmission line refers to the energy loss that occurs due to the leakage of electric current from the conductor. By using a very high-resistance dielectric, the transmission line can effectively minimize this leakage loss. A high-resistance dielectric material restricts the flow of current through it, preventing the leakage of energy. As a result, more energy is retained in the transmission line, leading to reduced loss and improved efficiency. Therefore, using a very high-resistance dielectric is the most suitable option for minimizing leakage loss in a transmission line.

The correct answer is "Wavelength is inversely related to frequency." This means that as the frequency of a wave increases, the wavelength decreases, and vice versa. This relationship is described by the equation: wavelength = speed of light / frequency. As the speed of light is constant, a higher frequency will result in a shorter wavelength. This relationship is fundamental in understanding the behavior and characteristics of waves.

The amount of skin-effect loss refers to the increase in resistance of a conductor as the frequency of the current flowing through it increases. This phenomenon occurs because at higher frequencies, the current tends to flow more towards the outer surface of the conductor, reducing the effective cross-sectional area available for current flow. Therefore, the skin-effect loss is directly proportional to the frequency of the current.

The characteristic impedance of a transmission line is determined by its inductance and capacitance. Inductance is the property that opposes changes in current flow, while capacitance is the property that opposes changes in voltage. These two properties work together to create the characteristic impedance, which is the impedance that a signal sees when traveling through the transmission line. The inductance and capacitance are influenced by the physical dimensions and materials used in the transmission line, such as the spacing between conductors and the dielectric material.

The wavelength of a signal can be calculated using the formula: wavelength = speed of light / frequency. In this case, the frequency of the signal is given as 250 megahertz (MHz), which is equivalent to 250 million hertz (Hz). The speed of light is a constant value of approximately 3 x 10^8 meters per second. By substituting these values into the formula, we can calculate the wavelength to be 1.2 meters.

When discussing resonant and nonresonant transmission lines, maximum power transfer actually results from a nonresonant line. Resonant lines, on the other hand, are often referred to as flat lines. It is important to note that using a nonresonant line can result in significant loss and damage to equipment.