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Military

CHAPTER 5

COMMUNICATIONS


Section I. GENERAL

5-1. Role

Military operations in northern latitudes may be characterized by the employment of independent task forces, usually beyond mutual supporting distance of each other. The lack of major land lines of communication, the necessity of relying upon air lines of communication, and the great dispersion between forces means that primary reliance must be placed on radio as a means of communication. Operations over extended areas will require augmentation of radio equipment and personnel. When these factors are considered in conjunction with the extreme cold and deep snow, it can be seen that, under some circumstances, operations of isolated task forces will be practically impossible unless these forces are able to communicate with higher and adjacent units to arrange for support and supply.

5-2. General Effect of the Environment on Communications

a. High frequency transmission and reception, while capable of spanning the extended distances dictated by tactical requirements, are subject to interference by magnetic storms, aurora borealis, and ionospheric disturbances, which may completely black out reception for hours, or even days. Transmission and reception under most conditions is possible providing proper installation and operation procedures are followed.

b. The combined effects of terrain, cold, ice, dampness, and dust on communications equipment increase maintenance and supply problems to the extent that the full effort of operators and repair personnel is required to provide satisfactory communications.

5-3. Support of Signal Communications Activities by Army Aviation

Army aviation should be used whenever possible to assist in overcoming the communication difficulties caused by terrain and extreme climatic conditions.

Section II. COMMUNICATION

5-4. Propagation Methods

a. Radio communications in the northern latitudes suffer from propagation difficulties and exceptional planning steps are essential for radio operations in northern areas. Emphasis must be placed on the selection and use of proper frequencies and if the radio propagation graphs, charts, and prediction data presently available are fully utilized.

b. In order to appreciate the effect that atmospheric disturbances such as the aurora borealis can have on radio communication, it is necessary to understand the methods by which radio energy from a transmitter can reach the distant radio receiver.

c. The transmission of a radio signal from a transmitter to a receiver can occur essentially in one of two ways; that is, by a direct path between the antennas of the transmitter and the receiver or by a reflection from a layer in the upper atmosphere called the ionosphere. The radiated signal from the transmitter is divided into two main components, the ground wave and the sky wave. The ground wave travels along the surface of the earth and has a relatively short range. The sky wave travels upward into space at all angles up to the ionosphere. The ionosphere is an electrically charged region which exists at altitudes of 40 to 250 miles above the earth and which has the property of reflecting radio signals back to earth just as a mirror reflects light. In this way long distance communication is possible; however, the ionosphere is variable and its action depends on the time of day or night, the season of the year, and the effect that radiation from the sun has on the reflective powers of the ionosphere. Also, it is selective in regard to frequency and the angle at which the radio waves arrive. Above a certain frequency (40 to 60 megahertz (MHz)), the greater amount of the energy in radio waves passes through and is not reflected.

d. Tactical radio equipment operating in the so-called line-of-sight frequency band (30 MHz and upwards--the frequency modulated series of tactical radio sets are included in this band) is not affected adversely by auroral activity. In fact, the greater ionization of the upper atmosphere which takes place during aurorals will, on occasion, increase the range of the tactical FM radios. The use of VHF and microwave radio relay equipment will provide the greatest degree of reliability for multichannel means of communications in northern areas. Tactical tropospheric scatter radio equipment, when available is another reliable means of providing multichannel communications for distances up to approximately 300 kilometers (186 miles).

5-5. The Auroral Effect

The reflecting properties of the ionosphere are directly related to the position and radiation activity of the sun. The sun's bombardment of the earth's atmosphere coupled with strong magnetic activity concentrated near the poles causes a visual effect that is called the aurora borealis in northern latitudes. Ionization of atmospheric particles is increased, and radio waves reaching distant receiving points by means of sky wave propagation are reduced in intensity by increased absorportion. This absorption becomes more pronounced during violent eruptions of the sun's surface which is visible in the form of sunspots. During such a period, a radio "blackout" may occur on nets crossing or passing through the auroral zone. The greatest auroral activity occurs between 60 and 70 North latitude and occurs at intervals of 27 to 28 days. Signals from distant stations are usually much stronger prior to such periods. Monthly predictions of expected conditions are published by the National Bureau of Standards and are available to communications-electronics staff officers at all levels of command. It must be emphasized that "blackouts" occur throughout the high frequency spectrum and down to 26 KHz and may last several days. In addition, high frequency sky wave transmissions are subject to sporadic blackouts which are, at present, unpredictable and erratic as to duration and coverage.

5-6. Atmospheric Static

a. In the medium frequency band (300 to 3,000 KHz) very little continuous high level static is experienced in northern latitudes, but steady rushes of high level noise are common and signify an auroral blackout on the frequency being monitored.

b. Flakes or pellets of highly charged snow are occasionally experienced in the North just as rain and sand static are encountered in many tropical and desert regions during periods of high winds. This phenomenon is commonly called precipitation static. Charged particles of snow driven against metal vehicles, antennas, and other objects usually discharge with a high pitched static roar that can blanket all frequencies for several hours at a time. While these phenomena are uncommon except in aircraft, they can take place just when communications are vital to some operations.

c. Antiprecipitation, static-proof antennas can be constructed by covering exposed portions of the antennas with layers of polystyrene tape and shellac to withstand breakdown voltages on the order of 30,000 to 40,000 volts. The value of such a system depends entirely on the station's isolation, since discharging particles on metal masts and other equipment near antiprecipitation receiving antennas can produce heavy static by radiation from the tiny sparks.

d. Very heavy shocks can be experienced from the unground lead-in of antennas subject to high winds or blowing snow even when the degree of audible static is not great.

5-7. Antennas and Grounds

a. Difficulties will be experienced in erecting antennas in the north. The frozen ground makes it difficult to drive the antenna ground, guy, and ground plate rods. Mountain pitons are considered excellent anchors for antenna guys in frozen earth, ice, or rocky soil. In addition, in extreme cold, ropes can be frozen to the ground and guys tied to these anchor ropes. Additional time must be allowed for these operations, and care must be exercised in handling lead-ins and metal masts since they become brittle in extreme cold. Vertical antennas are preferred for ground wave propagation in the high frequency band; but the use of fractional wave length whip antennas is not recommended, except for short distances.

b. All large horizontal antennas should be equipped with counterweights arranged so as to give before the wire or poles break from the pressure of ice or wind. Wet snow and sleet freezing to the antenna may be removed by jarring the supports.

c. Suitable grounds are difficult to obtain under conditions of extreme cold inasmuch as the frozen ground offers high electrical resistance. The permafrost which underlies much of the Far North offers as much obstruction to ground rods as solid reinforced concrete. Where it is possible to install a ground rod, the rod should be driven as deeply as possible into the frozen earth or preferably through the ice of one of the lakes or rivers that abound in the North. In many instances it will be impracticable to secure a ground and it will be necessary to install a counterpoise. In no instance should more than one transmitter be connected to the same ground or counterpoise, nor should electrical noise-producing items such as direct current, battery-charging generators, or metal-walled huts be connected to receiver ground systems.

5-8. Effect of Extreme Cold on Battery Power Supplies

a. Although extreme cold impairs the operation of the electrical components which make up radio sets, it has its most serious effect on the dry type primary batteries which are used to power the small man-carried portable radios and many of the test instruments used to repair signal equipment. To minimize the effects of cold on dry type batteries, only those batteries designed for cold weather operations should be used for northern operations.

b. Batteries of all types show decreased power capacity at low temperatures; specially designed cold weather batteries are more efficient. Batteries should be stored at supply points between temperature ranges of 10 to 36 F. Upon removal from storage, and prior to use, the batteries should be heated slowly to a temperature of 70 F. Warm batteries will give good results if used promptly upon exposure to cold. The conventional dry cell type battery loses efficiency rapidly at low temperatures and decreases in capacity as the temperature drops below 70 F. (The terminal voltage of the battery is not affected by cold, but its capacity, life, or effectiveness to supply operating voltage over a period of time is affected.) At 0 F. it is 40 percent effective; at -10 F., 20 percent; and at -30 F., only 8 percent effective.

c. Dry batteries, if kept warm, at low ambient temperatures, will deliver satisfactory service life. Carrying of batteries inside clothing, or the use of insulated containers or heating devices, to provide a warm temperature for the battery are satisfactory as long as the battery temperature is not permitted to exceed 100 F. Battery vests designed for wear under outer clothing, consisting of temperate type batteries of flat cell construction should be used with man-packed radio sets during extreme cold. The useful life of the battery can also be extended if it is warmed up prior to the time it is placed in operation in the low ambient temperatures. Batteries which become inactive because of the cold may be reactivated by a thorough warming at temperatures below 100 F. A battery no longer serviceable in cold weather may be used indoors where the temperatures are warmer.

5-9. Electronic Warfare

The low temperatures, low visibilities, and the lack of ground lines of communication in the northern regions impose greater reliance upon radio type devices for command and control of ground combat forces. Radio navigation aids, so necessary because of the scarcity of landmarks, prevailing low visibility, and the long hours of darkness, are particularly sensitive to electronic warfare measures; this is especially true where alternate base stations are few and far between. On the other hand, the enemy must also rely upon electronic aids and a small electronic warfare unit properly employed can play a decisive role in northern operations.

5-10. Techniques and Expedients for Increasing Range and Reliability of Radios

a. For effective application operators require special training initially and refresher training prior to commitment to northern operations. Training of tactical FM radio operators in special techniques is particularly important because these personnel normally have no formal training. Consideration should also be given to the additional training requirements for Radio Telegraph, SSB-voice and other HF radio sets recommended for Northern operations.

b. Where radio communication is the primary means of signal communication, it is essential that the following techniques be followed at all times:

(1) Operators must be completely familiar with their set. They should read and understand the technical manual which is part of each radio.

(2) Operators should keep the radio set clean, dry, and as warm as possible.

(3) They should handle the set carefully. Radios that are exposed to extreme cold are particularly sensitive to jars, shocks, and rough handling.

(4) Preventive maintenance procedures take on added importance. Operators should detrained to setup a routine inspection and check procedure covering the following points:

(a) Plugs and jacks should be clean.

(b) Antenna connections should be tight. Insulators must be dry and clean; snow and ice removed.

(c) Power connections must be tight.

(d) Motors and fans should run freely.

(e) Knobs and controls should operate easily.

(f) Lubrication must be checked more frequently.

(g) Dry batteries must be fresh and kept warm.

(h) Operating spares must be on hand.

(i) Breath shields should be used on all microphones.

(j) Additional guying for antenna masts is required to prevent mast failure cause by severe cold and extremely high winds.

(k) Insure that the proper antenna length is used relative to operating frequency.

(l) Check to assure that the antenna has been erected and oriented properly.

(m) Operators should insure that radios are turned off whenever vehicles are started. This is necessary to avoid a sudden surge of power. Before the radio is turned on the vehicle should be allowed to warm up inside.

c. With equipment in good shape, lack of communication can be caused by the following:

(1) Excessive distance between sets.

(2) Bad intervening terrain, such as hills and mountains.

(3) Poor choice of location of one or both ends of the radio net.

(4) Poor choice of operating frequency for sky wave.

(5) Poor choice of antenna; improper antenna orientation.

(6) Not enough transmitter power.

(7) Excessive noise and interference.

d. The following techniques and expedients can be used to increase the range and reliability of radio nets.

(1) Use the radiotelegraph (RATG) method of operation rather than the radiotelephone (RATEL).

(2) For tactical FM radios, elevate the antennas as high as possible either by siting the set on hills and mountains, using an elevated ground plane antenna, an improvised elevated half-wave antenna, or an improvised vertical half-rhombic antenna.

(3) Use remote control devices in order that stations may be sited in advantageous positions.

(4) Use intermediate voice or automatic retransmission stations for both FM or HF nets. Radio sets using a retransmission device can be used as intermediate relay stations.

(5) Use Army aircraft for radio retransmitsion or relay when out of normal range, or other means or retransmission as practicable. Either intermediate voice or automatic retransmission from the aircraft can be employed in many situations. This will often prove to be the only means of successful communication to isolated teams and units, and for long range patrols.

5-11. Radio Communications

a. Command radio nets must be established first and priority given to maintenance throughout the tactical operation. When an element moves out of ground wave range from its base of operations, retransmission points must be established or sky wave propagation will have to be depended upon when it is not possible to establish intermediate retransmission points. When it can be anticipated that distances are so long as to preclude communications with equipment normally available, higher headquarters should be requested to furnish communications support. Situations may arise where radio communications will not meet full expectation. Alternate means, such as messenger service, must always be included in the signal communication plan.

b. The establishment of air-ground circuits is of major importance in all tactical operations in northern latitudes because of the dependence on aircraft for airmobile operations, logistical support, observation, and messenger missions.

c. The use of low or medium channel-capacity VHF-UHF radio relay equipment mounted on small tracked vehicles will provide the most reliable means of communications to mobile task forces as low as battalion size organizations. Such equipment configurations should retain the same mobility and concealment requirements as the supported unit while providing reliable telephone communications not subject to northern propagation difficulties.

d. The use of the radio wire integration technique to extend both radio and wire circuits will be an important factor in successful communications.

5-12. Factors Affecting Wire Communications

Tactical wire communication has the same capabilities and limitations in northern latitudes as in temperate zones. Due to the distances involved and the difficulty of overland movement, wire communications may be limited to telephones serving local installations. If long distance wire communication trunk (telephone, teletype, facsimile, and data transmission) are required, radio relay systems which can be integrated into the wire system must be considered because of relative ease of installation, economy of transport, and other logistic factors. The installation of radio relay systems on mountain tops normally will be necessary for extension of long distance wire circuits. Extensive planning for installation, maintenance, and support of equipment and support and survival of personnel operating these mountain-top relay sites is mandatory. Consideration must be given to the fact that more time is required to install and maintain field wire lines during periods of extreme cold and deep snow. Batteries which are used to operate field telephones and switchboards are subject to the same temperature limitations as those used to power the small portable tactical radio sets.

5-13. Special Considerations Applicable to Northern Latitudes

a. Aside from the logistical considerations, the most difficult task in providing wire communication is that of constructing and maintaining the necessary circuits. Field wire may be laid on the snow, but must be suitably marked to facilitate maintenance. Below the tree line, trees, if high enough, may be used to support the lines. Initial circuit layout should include consideration of wire and cable routes with respect to expected vehicular and oversnow traffic, so as to minimize the damage from tracklaying vehicles and ski troops. Field wire lines should not be laid on ski trails which are used for troop movement; a separate communication trail should be broken and used. If the wire circuit is to remain in place during the warm season, particular care must be given to its placement through areas, such as lakes and muskeg, which may be impassable in summer and make maintenance impossible. Similar care should be taken to avoid locating wire lines in areas subject to snow and earth avalanches. Consideration must also be given to the effects of frost thrust and the shifting of ice masses.

b. Telephones, teletypewriters, facsimile equipment, wire carrier terminals, and telephone switchboards, must be operated in heated shelters. Batteries and battery operated equipment should be kept warm even when low temperature batteries are used. Microphones, telephones, and operators' sets must be provided with breathshields to prevent frost formation from disabling them. Further difficulties can be expected from switch malfunctioning and stiffening or breaking of associated cord and plug assemblies.

c. Grounds are extremely difficult to obtain in frozen soil. Grounding of wire equipment is necessary; however, special cold weather ground stakes should be used and should penetrate the frozen surf ace of the earth 1 meter (3') below the surface. It may be necessary to use special blasting devices to obtain a suitable ground. When a grounding rod cannot be driven 1 meter into the soil, it should be driven in at least 30 cm (12") and water poured around the base to increase conductivity. Because of the difficulty of obtaining grounds and the high resistance of the soil, simplex telephone and teletypewriter circuits, which utilize a ground return to complete the circuit, should not be used.

d. Due to the difficulties of resupply and the necessity of limiting basic loads to the bare essentials, the communications-electronics staff officer must make every effort to recover all available wire for subsequent reuse. He must plan his circuits, so far as possible, to facilitate recovery, taking into account that wire or cable laid in or on the snow is extremely difficult to recover because of the melting, refreezing, and drifting action that takes place around the wire. The initial supply of wire, supplemented by limited resupply, may constitute the only source of field wire.

5-14. Techniques of Wire Construction in the North

a. Field wire is most conveniently laid from the dispenser MX-306/G. When these dispensers are used, communication can be maintained constantly to check the continuity of the circuits and to furnish a means of communication to the wire team. The dispenser can be attached to a standard packboard and the wire laid by a lineman on skis or snowshoes. When the distance is such as to preclude the use of lineman on foot and the terrain prevents the use of oversnow vehicles, wire can be laid from dispenser by Army aircraft.

b. Oversnow vehicles equipped with reel units can be used to lay field wire or cable. If recovered field wire is available and has been properly serviced, it should be used in preference to wire from the dispensers, thus conserving the dispenser wire for critical situations. Field cable can be most effectively laid from drums mounted on reel units installed on the vehicle itself. However, the undertaking of a major cable construction project in temperatures below 0 F. presents a formidable obstacle. The cable sheath and insulation, unless warmed, is no longer pliable. The act of unwinding it, by force, without preheating it for several hours could damage it to the point of uselessness. A heated shelter should be provided for wire-laying crews. An arctic personnel shelter mounted on a truck or tracked vehicle provides a good facility for tactical wire or cable laying. The wire or cable can be kept reasonably warm and pliable as it is played out of the shelter. The wire or cable should be dressed immediately before it has a chance to become stiff from the cold. All cable for tactical use should be stored in heated storage areas before being transferred to the portable shelters used for laying the cable.

c. Army aircraft can be used very effectively to install field wire circuits between points difficult to reach by ground transport means. The wire is laid from the dispenser, MX-306/G. Individual dispensers are connected prior to payout to provide the required length. The course over which the wire is to be laid must be suitably described to the pilot and the terminal points of the circuit marked by smoke, panels, or lights. In making plans for construction using this method, allow for a 50 percent slack factor, and consider the wire beyond recovery and extremely difficult to maintain.

d. Often the communications officer will find it necessary to use a combination of the previously mentioned techniques to install a single circuit. Lines to isolated relatively inaccessible detachments, such as weather stations, radar sites, and observation posts, may require the use of vehicle-towed cargo sleds or man-pulled 200-pound sleds to transport the additional amount of wire necessary to complete the circuit. Rockets and rifle grenades in conjunction with the dispenser can be used to carry field wire several hundred meters across ravines and crevasses.

e. It is extremely important, both from the viewpoint of conserving labor and considerably reducing required quantities of wire, to keep field wire and cables from being drifted over by the snow. Cables and wire that interconnect two or more units in a command can be covered with snow so deeply in a single day that the loss of many man-days in recovering or maintaining the circuits may result. This can be avoided by pulling the cable from under the snow after each snowfall and allowing it to rest on top of the snow, or better still, by using trees or cut poles to support the wire for overhead type construction. Make allowance for drifting snow in deciding on the height above ground at which to support the lines.

5-15. Tactical Employment of Field Wire

Distances involved and the difficulty of supply will govern the extent to which field wire is employed. Every effort must be made to integrate the wire system with the radio system so that a complete electrical communication system is available for command and control.

Section III. VISUAL COMMUNICATION

5-16. Factors Affecting Visual Communication

Visual means of communication are particularly effective in air-ground operation, when atmospheric conditions or security requirements preclude the use of radio, and in mountainous country where the extreme ruggedness of terrain prevents the laying of wire but affords line-of-sight for siting of visual stations. Signal lamps may be used when the situation permits. Blowing snow, haze, ice, fog, and other atmospheric conditions may affect the range and reliability of visual signaling in the northern latitudes. Security requirements for visual means of communication are the same in the North as in temperate zones.

5-17. Panel Communications

The standard panels are satisfactory for air-ground signaling when displayed against a background of snow. It must be recognized that blowing snow can obliterate panels in a matter of seconds.

5-18. Pyrotechnics

a. Colored smokes most easily seen against snow covered backgrounds are, in order, red, violet, green, and yellow.

b. Smoke grenades, mortar and artillery marking rounds of the base ejection type will tend to be smothered by deep snow. Use of a time fuze to obtain air bursts will facilitate location of marking rounds. In using white phosphorus projectiles, the white phosphorus will tend to be smothered, and in addition, particles of phosphorus will remain to contaminate the area.

Section IV. MESSENGER

5-19. Special Factors to be Considered

Communication by messenger is frequently the only means available to units. In the uncharted areas of the northern latitudes of the world, the ability of messengers to find their way takes on added importance. Messengers should be good skiers, resourceful, familiar with northern peculiarities, and carry their own existence load. Messengers should always be dispatched in pairs.

5-20. Aircraft Messenger Service

Messenger service should be scheduled between units and should, if possible, be integrated with the aerial resupply missions. The use of helicopters for messenger service must be considered, as units will seldom be located near landing areas suitable for fixed wing aircraft.

5-21. Vehicular Messenger Service

a. Vehicles may be employed to maintain messenger communications between units when the conditions of time, terrain, and distance permit. At best, surface transportation is slow, subject to interception by ground ambush parties, and uneconomical with respect to fuel and equipment.

b. It is essential that all vehicles utilized for messenger service over infrequently used routes possess the capability of oversnow operations, and be equipped with radio, emergency equipment snowshoes, heating apparatus, and simple navigational equipment. It is likewise essential that messengers be trained in radio operation and ground navigation. When security permits, the vehicle should be kept in continuous communication with its headquarters. The unit to which the vehicle is destined should be informed by enciphered radio message as to the time of departure and expected time of arrival.

Section V. PHOTOGRAPHY

5-22. General

Photographic equipment is generally designed to operate in temperate climates, under cold weather conditions camera equipment will operate in a sluggish manner and film emulsions acquire different sensitivity. The information below was provided through the courtesy of the Eastman Kodak Company. This information is designed to minimize the cold weather effects on cameras and associated equipment.

a. Effects of Cold on Photographic Equipment.

(1) Leather, rubber, and photographic film become stiff and brittle at low temperatures. The lubricating oils used in cameras congeal so that moving parts will not operate. Film speed is lowered by the cold and at -50 F, will be approximately one lens opening slower than at 60 F.

(2) Film will become progressively more brittle as the temperature drops. Care should be taken to retain film in its original container until it is ready for use. It has been determined that film that retains its moisture content will remain more flexible at low temperatures than film that has been allowed to dry out. Film can be bent with the emulsion side in with less chance of breaking them if bent with the emulsion side out. Whether the film breaks at low temperatures will depend on the care taken in handling it and the type and condition of the camera using it.

b. Camera Equipment.

(1) Whether or not photography will be successful during cold weather operations depends on the selection of the proper camera. Some cameras wind the film with the emulsion side out, this places undue strain on the film and will sometimes cause film breakage. Cameras that wind the film with the emulsion side in will generally perform satisfactorily.

(2) Cameras that use the film to cock the shutter should be avoided because they will almost always break the cold film.

(3) Cameras using film packs should be avoided because of the sharp bend the film has to make when the tab is pulled.

(4) Generally it is better to use a motion picture camera that uses a film magazine because of the difficulty encountered in threading roll film during cold weather conditions. A lightweight portable camera is desirable. Electric power, if available, from a reliable source is more dependable than spring-driven motors. Under field conditions, however, the spring-driven motor may be more reliable than an electric motor drive that depends on batteries for its power.

(5) Cameras should be winterized prior to use in cold temperature areas. This is accomplished by dismantling the camera and removing all old oil or grease. Relubrication should be accomplished with special low temperature lubricants. Cameras that have been winterized should not be used in a temperate climate unless they are relubricated.

(6) Motion picture cameras that have been winterized should be thoroughly broken in prior to actual use. This can be accomplished by splicing a piece of film 3 to 4 feet long end-to-end threading it in the camera and allowing the camera to run 3 or 4 hours. In magazine type cameras the loop should be formed in a dummy magazine. After the breaking in period, the camera should be checked for speed and general behavior. Still cameras should be given break-in conditioning by operating all moving parts enough to insure that they operate smoothly.

(7) All cameras should be protected from cold winds as much as possible during use. When battery driven motors are used on cameras they should be kept as warm as possible. Miniature cameras and small motion picture cameras should be carried underneath the parka or field jacket to obtain body heat.

(8) The lens should be inspected each time before use. Static electricity generated during periods of cold-dry conditions will attract pieces of lint to the lens. This lint should be removed prior to taking a picture.

c. Batteries. All types of batteries lose efficiency when cold. After a few hours of exposure to cold, the batteries used in flash holders and electronic flash power packs become so weak that they will not operate the flash equipment. Photographers should keep their batteries underneath outer clothing to obtain body heat. For extended shooting several sets of batteries should be used so that one set can be warming while the other is operating. Since fresh batteries will operate at colder temperatures than partially used ones, every cold weather shooting session should start with the freshest batteries available.

d. Picture Taking Techniques.

(1) Certain cold weather precautions should be observed with any type of camera. Breathing on the lens will cause condensation that freezes instantly and is difficult to remove. Unpainted metal surfaces should not be touched with the bare skin because of the possibility of the skin freezing to the surface. A painful loss of skin is the end result. Cameras, and other equipment with optical lenses should not be brought into heated rooms without careful, slow warming. This is necessary to prevent cracking of optics and to prevent condensation. Conversely, a warm camera cannot be taken out into a snowstorm because the snow hitting the camera will melt and turn into ice.

(2) Camera shutters, especially focal-plane shutters, operate more slowly as the temperature falls. In general, faster shutter speeds are more affected than the slower speeds, although no two shutters behave the same. When taking pictures during cold weather the shutter should be snapped several times at 1/10-second to insure that the shutter is operating. It is also a good practice to leave the shutter uncocked until just prior to taking the picture. This will prevent the shutter from freezing in a cocked position. Because of the slow-down in shutter speed, exposure determination becomes problematical. It is therefore advisable to make several exposures broadly bracketing the correct exposure.

(3) Since shutter controls, focusing mechanisms, and diaphragms may freeze, it is well to preset the camera indoors. Set the shutter and diaphragm for the nominal value of exposure to be expected under prevailing conditions. Then set the focus for the hyperfocal distance for the selected aperture. Focusing the lens on the hyperfocal distance gives the greatest depth of field for any particular aperture. With the camera preset in this fashion, even if all of the controls freeze, as long as the shutter continues to operate, pictures can be made.

(4) Film in any camera can be changed during a driving snow storm if a dark plastic bag big enough to fit over the head and shoulders is used. A deep lens hood should be used for filming in the snow because it will help keep the lens dry even during a fairly severe storm.

(5) Flash bulbs have a greater tendency to shatter at low temperatures, so caution must be exercised in their use. Light reflected from snow close to the camera can cause lens flare, even though standard lens hoods are used. To insure better synchronization at low temperatures, it is advisable to set the shutter at 1/25.

(6) Roll film must be advanced slowly and steadily to avoid static marks and breaking the film. For the same reason, filmpack tabs must be pulled slowly, steadily, and straight. Static markings are caused by an electrostatic discharge and they appear on the developed film emulsion as marks resembling lightning, tree branches, or nebulous spots. When static difficulties occur, they can usually be traced to the use of film which has a low moisture content or rapid handling of the film which build up static electricity.

(7) Sheet-film holders are often a source of trouble when they become cold. The plush light-trap becomes rigid and does not close after the slide is withdrawn. This can be avoided by not pulling the slide all the way out. If this is not practical, cover the back of the camera with the focusing cloth when removing the slide, during the exposure, and while reinserting the slide. When reinserting the slide, do it squarely, not one corner first.

e. Selection of Film.

(1) In general, field photography in cold weather areas involves subjects of extremely low brightness scale and very high levels of illumination. For this reason, high-speed emulsions are not generally used outdoors. The best choice of film is a medium-speed material or even slower, finer-grained film.

(2) Under field conditions during periods of cold weather, one camera is all that one photographer can efficiently manage. Therefore, if pictures are desired in both color and black-and-white, a color negative film should be used. From the color negatives prints can be made in either color or black-and-white and color slides can be made from the same negatives.

5-23. Aerial Photography

Aerial photos of snow covered terrain will not disclose as much terrain detail as one of the same area barren of snow. On the other hand trails and tracks in snow show up in great detail on aerial photographs and are excellent sources of information.

Section VI. MAINTENANCE AND CARE OF EQUIPMENT

5-24. General

Standard types of signal communication equipment can be used at very low temperatures with satisfactory results if proper precautions are taken and the equipment is properly winterized. Provisions must be made in the operation plan to include the special maintenance requirements necessitated by operations in extreme cold. As a general rule, signal communication equipment should be installed and operated in a warm shelter. Warm shelters are an absolute necessity for maintenance personnel. The general principle of keeping equipment warm and dry, in addition to following winterization instructions closely, will insure the best possible performance of signal communication equipment. Further information relative to maintenance of signal equipment in northern latitudes is contained in Signal TB.

5-25. Rubber and Rubber-Like Compounds

Rubber and rubber-like compounds become increasingly stiff and brittle as their temperature is lowered. When cold, cordage should be flexed slowly and carefully in order to minimize breakage. Power cables and coaxial cable transmission lines should be warmed before they are laid in the open. Frequent failure of cables of these types, and of field wire, may be expected if it is necessary to recover and rereel them during extreme cold. Increased requirements for replacement should be anticipated. Where possible, contact of rubber items with fuels and lubricants should be avoided. Where feasible, rubber items should be warmed before flexing.

5-26. Radio Receivers and Transmitters

Upon exposure to extreme cold, radio receivers and transmitters adjusted for operation in a relatively warm place may exhibit, in their frequency determining circuits, changes of sufficient magnitude to impair their operation. Low battery voltage will also have a detrimental effect on frequency determining circuits. All radio operators must be trained to make frequent checks for proper frequency. It is particularly important that the operators at the radio net control stations be alert to this condition and that they require the secondary stations of the net to make necessary adjustments to keep them on frequency.

5-27. Microphones

Moisture from the breath freezes on the buttons and perforated cover plates of microphones, causing the instrument (telephone, radio, etc.) to become inoperative. Standard microphone covers are available and should be used in northern latitudes during periods of extreme cold. If the standard cover is not available, a cover can be improvised by using a thin cellophane or cloth membrane.

5-28. Mechanical Malfunctions

Plugs, jacks, keys, shafts, bearings, dials, switches, and camera shutters are subject to malfunctioning caused by the differential contraction of metal parts in extreme cold. The result is binding, difficulty in turning and adjusting, or complete locking of the part. In addition to the trouble caused by differential contraction, moisture condensation which freezes in such assemblies will also render them inoperative. Moisture condensation caused by localized heating may freeze in subassemblies during shutdown periods and may render them difficult to operate, or even inoperative.

5-29. Breathing and Sweating

Any equipment which generates heat during operation will "breathe" or draw in cold air as the equipment itself cools. If such heated equipment is brought into contact with extremely cold air, the glass, plastic, and ceramic parts may break. "Sweating" is the reverse of the process described above. If cold equipment is brought into contact with warm air, the moisture in the air will condense on the equipment and will subsequently freeze when the equipment is brought into the cold again. Cold equipment should be wrapped in a blanket or parka before being brought into a heated shelter.

5-30. Wire Insulation

Extreme care must be taken in handling insulated wire and cable at subzero temperatures, as the insulation tends to become stiff and brittle and liable to cracking. Insulation is especially vulnerable at such points as field wire ties and splices. Rubber and plustic covered cables should be warmed before bending so as to minimize the possibility of breaking the insulation. Coaxial cable is particularly critical because the inner plastic insulation may crack. Standard friction and rubber tape lose their adhesiveness when subjected to extreme cold. Splicing of field wire and cables is a problem because the hands must be protected by mittens or gloves which restrict handling. Special cold-weather type electrical insulating tape is available and may be used without prewarming.



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