FM 24-18: Tactical Single-Channel Radio Communications Techniques
The power required to operate radio equipment may come from a variety of sources, such as commercial power, dry batteries, storage batteries, engine-driven generators, and rectifiers. Each type has certain advantages and certain limitations. Depending upon the application involved, these sources of power may be used individually or in combinations.
A-2. Commercial Power
Various values of AC and DC voltages can be obtained from commercial powerlines and used as primary power sources. The AC voltage sources range from the standard 115-volt, single-phase power source to the 2,300 volt, three-phase power used for industrial purposes. The primary DC voltage sources range from 28 to 440 volts. Power supplies designed for AC operation must not be connected to a DC source, since this will damage the power transformer. Also, equipment designed exclusively for a DC source will not operate on AC power.
A-3. Power Converters
Because of the wide variation in commercial power in various parts of the world, and because of the special power requirements of certain types of communications equipment, it is frequently necessary to make changes in the available power. It may be desired to convert AC to DC, or DC to AC. It may be necessary to provide 60-hertz current from a 25-hertz power source, step the voltage up or down, or convert single-phase power to multiphase power. Electronic converters, motor generators, or transformers may be used singly or in combination to effect these changes. The choice of equipment depends on the desired result and the available power sources.
Electronic converters are devices that change AC to DC, DC to DC, or DC to AC. There are no moving parts used in the conversion process. Instead, electronic devices such as transistors and electron tubes are used. Electronic converters that change AC or DC to DC are commonly called DC power supplies, while those that change DC to AC are called inverters.
Most AC devices for communications systems are designed to operate at 50 to 60 hertz from a 115- or 230-volt power source. In many areas, however, the available voltage is unsuitable for the operation of such equipment. Therefore, power transformers are used to increase or decrease the AC output voltage to the values required.
Solid state power inverters.
Solid state power inverters are used in power units that supply power requirements to both vehicular and conventional radio systems because they may be designed to operate from both AC or DC voltage inputs. They are highly versatile, and are capable of providing wide ranges of AC and DC voltage outputs. These inverters may be designed to produce AC outputs at the standard 60-hertz line frequency or at higher frequencies which facilitate the design of lighter and smaller power units, filtering systems, and associated equipment. These inverters may be designed to convert either AC or DC input voltages into a square wave pulse train, transforming this train to the desired voltage level. Where DC outputs are required, the inverter rectifies and filters this voltage to a smooth and ripple-free DC power source. Normally, these power units incorporate solid state voltage regulator circuits and protective circuitry designed to shut down the affected power sources during hazardous malfunctions of associated equipment.
|WARNING: Observe all warning labels on batteries. Severe injury or death may result if they are mishandled or disposed of incorrectly.|
There are distinct advantages to be realized through the use of batteries as a source of electrical power for both radio communications equipment and test, measurement, and diagnostic equipment (TMDE). They allow complete mobility of the equipment involved and provide complete isolation from noisy power generating systems. Such systems produce electrical power which is often laden with transient spikes and pulses that tend to interfere with communications and prohibit accurate measurements. The recent breakthrough in battery design, development, and manufacture has produced a greater dependability and versatility of batteries as a source of power. Consequently, the military inventory of battery-powered equipment is steadily on the increase. Some of the items currently in use which use a variety of sizes and types of batteries are listed in table A-1.
Table A-1. Partial List of Items of Equipment That Use Batteries
The complete inventory of radio communications equipment is too extensive to list in this manual. The items cited above are mere illustrations of the general uses of batteries in radio equipment. The inventory of TMDE equipment using batteries as a source of power is comparably extensive. The installation and preventive maintenance procedures for batteries are given in the specific operator's manual for the equipment which uses them as a source of power. Therefore, no procedures are given in this manual.
A battery consists of a number of cells assembled in a common container and connected together to function as a source of electrical power. Batteries are widely used as power sources in portable radio communications equipment because of their inherent stability. Batteries are also widely used in TMDE. Modern technology has produced a wide range of batteries, each unique in itself in meeting some particular power requirement. Development of new and different types of batteries in the past decade has been so rapid that it is impossible to present a complete knowledge or description of them in this manual; however, some of the common types currently used in radio and TMDE are described below.
With the advent of small transceivers and miniaturized equipment, a very small battery was needed that was capable of delivering maximum electrical capacity per unit volume while operating in varying temperatures and at a constant discharge rate. The mercury battery, which is one of the smallest batteries, meets these requirements.
The lead-acid battery is used extensively throughout the world. It is an electrochemical device for storing chemical energy until it is released as electrical energy. Active materials within the battery react chemically to produce a flow of direct current whenever current consuming devices are connected to the battery terminals. This current is produced by chemical reaction between the active material of the plates (electrodes) and the electrolyte (sulphuric acid). It is primarily used as a vehicle battery, but it can be, and is being used in larger communications equipment and shelters.
The nickel-cadmium batteries are far superior to the lead-acid type. Some are physically and electrically interchangeable with lead-acid types. Smaller units are designed to be used inside radio, TMDE, and electronic equipment. The nickel-cadmium and lead-acid batteries have capacities that are comparable at normal discharge rates, but at high discharge rates the characteristics of the nickel-cadmium batteries are far superior. They can deliver a large amount of power and can maintain an almost constant voltage level until discharged. They can stay idle in any state of charge for an indefinite time and keep a full charge when stored for long periods of time. They may be charged and discharged any number of times without any appreciable deterioration. Due to their superior capabilities, nickel-cadmium batteries are being used extensively in many military applications that require a battery with a high discharge rate. In many instances they are replacing lead-acid batteries in vehicles.
Zinc-carbon is the most widely used type of battery. They are commonly called dry cells or dry batteries because the electrolyte used is in paste form and sealed, making it virtually impossible to spill. The ampere hour of these batteries is not a fixed value but varies with current drain, operating schedule, cut-off voltage, temperature, and battery storage techniques and duration. These batteries have four general areas of application: (1) radio, (2) general purpose, (3) flashlight and photo-flash, and (4) heavy duty industrial. The dry cells vary in chemical composition, depending on the application for which they are intended. Thus, a dry cell battery intended for radio applications contains a higher percentage of active electrochemical materials than a battery intended for photo-flash operation. This higher percentage of electrochemical materials increases the overall capacity of the battery, enabling it to remain in service longer than a similar size battery designed for photo-flash operation. Conversely, a battery intended for photo-flash applications contains a higher percentage of carbon which lowers the internal resistance and impedance of the battery enabling it to deliver the required higher current for a short duration. Although either of these classes of batteries will operate in another application, the most satisfactory results are obtained when each type of dry cell or battery is used in the application for which it was specifically designed.
The electrochemical system of both nonrechargeable (primary) and rechargeable alkaline cells comprises a zinc anode of large surface area, a manganese dioxide cathode of high density, and a potassium hydroxide electrolyte. These batteries have low internal resistance, low impedance, and high service capacity. They are hermetically sealed. The nominal voltage of a single alkaline cell is 1.5 volts; however, the closed circuit voltage of an alkaline primary battery falls gradually as the battery is discharged. Consequently, the service hours delivered by alkaline/ manganese primary batteries are far greater than that of zinc-carbon batteries as the end point voltage is lower. Service capacity remains relatively constant as the discharge rate is varied and the capacity does not vary as much with current drain as it does in zinc-carbon batteries. The alkaline system operates with high efficiency under continuous or heavy duty and high drain conditions where as the zinc-carbon battery is unsatisfactory. Under certain conditions, alkaline batteries will provide as much as ten times the service of standard zinc-carbon batteries.
The lithium-nickel halide battery represents a potential for a dense, high energy source of electric power. Extensive research is in process to develop this extraordinary, high current producing battery. Lithium is the Earth's lightest solid element, weighing only one-thirtieth as much as an equal volume of lead. It can, however, generate up to eight times as much electricity when coupled to a suitable cathode in the presence of a suitable electrolyte. Because of their high current producing capabilities, lithium batteries are being developed for use as power sources in electric cars and forklifts. Some lithium-type batteries have already been fielded for some types of Army radio equipment. For example, The BA-5590/U is used in the KY-57 (Vinson) and the BA-5598/U is available for use in the AN/PRC-25, -77, and -74 radio sets. Others are in the process of distribution.
Safety features. The battery is protected by a 3.5 ampere blow replaceable fuse in each 12-volt section to protect against excessive currents of external short circuits which could lead to overheating, cell venting, or rupture. This fuse should not be bypassed or replaced with a higher rated fuse. Each cell (ten per BA-5590/U) is designed with a venting device which releases internal cell pressure to ambient pressure if the internal pressure exceeds 350-450 psia. Venting will occur when pressures become excessive due to cells which have overheated (200-220øF) and serves to prevent the cell from rupturing. If a cell vents, sulfur dioxide gas will be released, which is a noxious eye and respiratory irritant. Irritation will occur long before toxic concentrations are reached and serves as an indication of its (SO2) presence. This battery contains no radioactive material.
Storage. Bulk storage of BA-5590/U batteries should be in a well ventilated cool temperature facility (about 70øF). Refrigeration is not required. Battery life decreases with storage time and with increasing temperature. For this reason, temperatures above 130øF should be avoided if possible.
Handling. The BA-5590/U battery contains pressurized cells similar to aerosol cans. Therefore, under no circumstances should the battery be deliberately opened, crushed, punctured, disassembled or otherwise mutilated. Rupture of the cell could occur. The BA-5590/U battery should not be heated or incinerated, as overheating may produce internal pressure at a rate in excess of the venting capacity and could result in a cell or battery rupturing. Under no condition should the batteries be recharged. Such action could lead to venting, rupturing, or rupturing with fire.
Transportation. Shipment of the BA-5590/U battery is regulated by the Department of Transportation in 49 CFR 173.1015 in conjunction with 49 CFR 172.101 Hazardous Materials Table and DOT-E-7052 exemption for shipping of charged lithium batteries. 49 CFR 173.1015 addresses the shipping and general transportation of depleted lithium batteries.
Disposal. Batteries must be turned in to the local property disposal officer for disposal.
Overheating. In the unlikely event that an equipment operator detects the battery compartment becoming unduly hot, hears cell venting (hissing sound), or smells the irritating sulfur dioxide, he should immediately do the following:
- Turn off equipment.
- Do not remove the battery.
- Place equipment away from area of operation and, if possible, in a well ventilated fire protected area; allow 4 hours for battery to cool (battery should be cool to the touch).
- Carefully remove the battery from the equipment using available face and hand protection, such as safety shields, safety goggles, and protective clothing. Materials should not be picked up by hand. Use tongs or a scoop shovel.
- If the battery cannot be removed, leave the immediate vicinity of the equipment.
- Dispose of the battery properly if it can be removed.
Fire. In the event there are fires in which lithium batteries are involved, use a graphite powder, such as LITH-X or any other class D flammable metal fire extinguisher. If not available, these fires are generally extinguishable with water in sufficient amounts so as to flood the burning materials. This will not only tend to cut off air access to the fire, but will cool down the batteries and surrounding combustibles so that cell venting and burning are minimized. If many cells have ruptured, lithium metal may be exposed. Burning lithium metal may respond satisfactorily to treatment with water. However, if not, efforts should be aimed at preventing the spread of the fire to other combustibles while letting the lithium metal burn itself out. Carbon dioxide extinguishers will not extinguish burning lithium metal but will extinguish other combustible materials within or near the battery.
Voltage delay. If there is a delay in the operation of the equipment that exceeds 2 minutes, the battery should be replaced.
Battery removal. When equipment will not be used within 30 days, the battery should be removed from the equipment.
A-5. Engine-Driven Generator Units
DC engine-driven generators have output capacities of from 0.4 to 15.9 kW. AC engine-driven generators have output capacities of from 0.3 to 1,000 kW. In addition, there are certain special purpose generators that provide both AC and DC output.
Power unit noise reduction at forward area sites.
The procedure outlined below is designed to reduce power unit noise by approximately 90 percent and to increase survivability to direct fire.
Construct a dugout with adequate clearance along the sides and top to provide sufficient space for maintenance and ventilation of the engine-driven generator.
Locate the dugout preferably on a slight rise or hill so that accumulations of water and rain will be drained off. Dig drainage ditches leading away from the low side of the dugout.
Reinforce the sides of the shelter with sandbags, or a wooden or steel framework, to provide support and to prevent cave-ins.
Erect a roof of available material to provide protection from the weather. Allow space for a ventilator shaft to carry exhaust fumes away. (An exhaust system may be improvised by using flexible metal pipes or fiber carrying cases for artillery ammunition.) Ensure adequate space around the exhaust system for ventilation and cooling.
Drape empty sacks or canvas along the roof overhang to muffle generator noise.
Camouflage the dugout with available material that matches the surrounding terrain.
Power source substitution.
Power units that are recommended for specific equipment usually give the best results. In emergency situations, however, use any power unit of appropriate output voltage, current, wattage, and frequency. Sometimes spare equipment is available to provide additional output power. In such cases, it is recommended that only as many units be used as are required to carry the load.
In case of emergency, turn off all equipment and lights except those actually required to keep the circuits in operation.
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