Name
Instructor
Course
Date
Antennas This report provides details of different types of antennas used in ships as well as maintenance procedures and precaution measures when dealing with antennas. An Antenna is a component capable of radiating and capturing radio waves. Thus, antennas are useful elements of a ship and together with radio equipment are a means of communication between the vessel and the control tower. The first type of antenna used on ships is the quarter wave vertical antenna widely used at all frequencies from MF to VHF. The quarter wave vertical antenna is simple to construct and erect in locations with limited space like a ship. For VHF and UHF, it is important to elevate the antenna above close obstacles. One advantage is that, the single element vertical antennas have a multi-directional radiation design meaning they do not require re-alignment in a mobile application and are thus suitable for ships. A quarter wave aerial with a quarter-wave radials exhibits 50-ohms impedance thus uses a 50-ohm coaxial cable (Stutzman and Thiele). In summary, the quarter wave antenna is popular for its convenience and simplicity. The second type of antenna is the dipole antenna that is one of the commonly used RF antenna types. Primarily, it consists of two poles into which radio frequency current flows and together with a voltage causes radiation of a radio signal. There are several types of dipole antennas that include, half wave dipole, multi-half wave dipole, folded dipole, short dipole, and non-resonant dipole antennas. Dipole antennas exhibit 75 ohms impedance thus uses a 75-ohm coaxial cable (Stutzman and Thiele). The fourth antenna type is the yagi antenna used widely for directive antenna applications. It has a dipole as the central radiating component and three types of elements that are, the driven element, reflector and the director. Furthermore, it is designed to pick both VHF and UHF transmissions. Some advantages of the yagi antenna are; it allows reception of lower strength signals, and it simplifies the construction by allowing elements made from rods. Some disadvantages of the yagi are; it becomes too long for high gain levels that are limited to about 20dB for a single antenna (Poole). Several factors are considered when positioning or replacing the antenna. Primarily, high voltages are present near the antenna, and thus the equipment should be unplugged from the power source as well as the main fuses removed. Additionally, grounding the antenna is necessary, as there is the induction of RF energy from other antennas nearby. Although such induced voltage may not cause injury, an accident may still occur, for example, the technician may fall off the ladder. Maintenance of the ship antenna system should be a continuous process. Primarily, cleaning the antennas and frequently checking the feeder is vital in the preventive maintenance process. Another maintenance procedure is the covering of insulators with silicone to prevent salt-water penetration. In addition, safety loops on a wire antenna to prevent the antenna falling in case of undue strain are used. Lastly, a spare wire antenna stored in an easily accessible place carried on board in the event of an emergency is required. There are several test instruments for a malfunctioning radio system. The first instrument is the frequency counter used for measuring frequencies. Some precautions observed when using the instrument to enhance the accuracy of results include, not overloading the input, frequently calibrating and locking all time bases to a single clock. Another test device used is the spectrum analyzer used to analyze the frequency spectrum of radio frequency and audio signals. Hints to ensure optimal performance include, being aware of the input level, determining if the spurs are real and waiting for self-alignment. Finally, there is the oscilloscope used to display signal voltages on a screen in two-dimensional formats. While using an oscilloscope, it is important to beware of the bandwidth limitations, ensure correct triggering, and use the right probe. In addition, one must remember to calibrate the oscilloscope probe and beware of ground clips for high-speed measurements. While carrying out maintenance, some spare parts that are necessary may include the following. Firstly, one will need to have antenna coax connectors because these tend to cause problems due to frequent physical abuse. Secondly, one will need to have replacement batteries for the radio, as batteries tend to wear out with time. Thirdly, RF power modules are necessary; they usually blow off and will need continuous replacement. In addition, coax seal is essential to seal the coaxial cables that often stripped off thus exposing them to water. Below is a detailed diagram of a vessels antenna displaying the frequency bandwidth of antennas. [pic]

1. MF/HF SSB antenna It shows two types of antennas used in the sea. The first is the MF/HF that is a high-frequency antenna with frequency bands of between 3 to 30 MHz and utilized in the deep sea for distress calls (Poole). The second antenna is a single-sideband (SSB) modulation antenna that uses electrical and power bandwidth

2. Antenna tuning unit This device links the antenna and the transmitter to transmit frequency

Technicians working on antennas expose themselves to various radio frequency hazards. Firstly, radiation produces heat that is harmful to the human body and causes burns that could be deep and penetrating third-degree burns. In addition, there is also dielectric heating that causes a rise in body temperature to persons in an RF field. Vital body organs are susceptible to this and technicians must not stand in the field of RF radiating devices. Technicians, therefore, should be careful when working on antennas. Like any other place, there is a procedure when working on board a ship. To begin with, all people on board should have undergone training on safety measures and precautions. The training covers lifesaving and firefighting procedures. In addition, all individuals working aloft should be aware types of rope knot types and their usage on board a vessel. Furthermore, reporting of all accidents immediately they occur is a requirement. Lastly, all work performed is within defined procedures to achieve specified quality standards In conclusion, antennas and radio systems are vital components of a ship for the purposes of communicating when in deep waters. Thus, maintenance of the antennas and radio systems is critical to keep them in good working condition. However, technicians should be wary of their safety as they work on the antennas and adhere to the standard procedures while working on the antennas on board. In addition, technicians should be aware of the risk caused by radio frequencies and take measures to protect themselves against them.

Works cited
Poole, Ian. 'Antennas And Propagation:: Radio-Electronics.Com'. Radio-electronics.com. N.p., 2015. Web. 11 Mar. 2015.
Stutzman, Warren, and Gary Thiele. Antenna Theory And Design. 3rd ed. John Wiley & Sons, 2012. Print.