Technical Manual, U.S. War Department, October 1, 1944
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Chapter X: Equipment
Section IV: Signal Equipment
1. GENERAL. The following data have been derived from the examination of Japanese signal equipment.
2. RADIO EQUIPMENT. a. Ground. (1) The Japanese place most emphasis on wire communication. However, radio is used initially where communications must be established rapidly or where other means are not practicable. After wire communications have been established, radio assumes a secondary role as a stand-by communication link except where other means cannot be employed.
(2) Apparatus, to date, is of obsolescent design. Circuits and components are comparable with those used by the Allied Nations between 1935 and 1937. Transmitters and receivers almost invariably have wide frequency ranges and use plug-in coils to cover the various bands. In regiments or smaller units, transmitters generally vary from approximately 1 to 50 watts. High-powered sets (500 watts and above) are used primarily for Army administrative traffic and air/ground liaison. Simple Hartley oscillator circuits, connected directly to the antenna, are used. The smaller receivers employ regenerative detectors without radio frequency amplification. While such arrangements are simple to service and maintain, the frequency stability suffers greatly. It therefore would be difficult to "net" these radio sets and keep them on frequency.
(3) A great variety of small transceivers and transmitter-receiver combinations of 1 to 2 watts power are in operation. Such sets are usually man-pack. The transceivers are contained in one case which is carried on the chest; the batteries are carried in another case on the back. In the small transmitter-receiver models, the transmitter, receiver, batteries, and the hand generator for transmitter power, are all carried in separate cases, making it necessary for two to three men to pack and operate a set. Sets of from 10 to 50 watts power are usually of the portable type, and are carried in 4 or 5 separate cases. Power connections are made by means of plugs and cables. The sets, in general, have a complexity of control which does not permit ease of operation. The many controls of the Direction Finder and Intercept Receiver, Model 94 (1934), Type 1, indicate that a comparatively long time is necessary to obtain an accurate "fix" on a transmitter. It must be borne in mind, however, that Japanese operators are well trained and capable of making good use of their equipment.
(4) Most of the transmitters have provision for crystal operation, and, although few crystals have been found, it is reasonable to assume that crystal operation is used extensively. All crystal operated Army ground sets also can be employed as master oscillators.
(5) Since many ammeters, both for antenna and power, are supplied with separate shunts, the same meter movement can be used for many different sets.
(6) Examination of equipment shows that there is little indication of moisture- or fungus-proofing.
(7) All phone transmitters are amplitude modulated, and there is no evidence of frequency modulation.
(8) Technical characteristics and photographs of sets used by Japanese ground forces are illustrated in figures 337 to 354.
b. Airborne. (1) Japanese airborne transmitters and receivers, sturdily and compactly constructed, are of excellent workmanship and material. More attention appears to have been given to compactness of design than to ease of maintenance. In many instances, the equipment is so constructed that it is difficult, or even impossible, to service. To some extent, sets are designed to fit a particular type of aircraft, rather than standardized for general use. It has been noted that some tubes (valves) are equipped with leather handles to facilitate removal. Japanese equipment uses a large amount of aluminum, so that even bulky pieces are unusually light in weight. Although no precautions have been taken against corrosion and fungus control, reports indicate that equipment later than 1940 is far superior to that of earlier design. Electrically and mechanically, new radio equipment appears to approach Allied standards.
(2) It has been noted that not all Japanese planes have radio equipment. While radio direction finders are standard equipment on medium and heavy bombers, there have been no reports indicating that they are normally fitted to fighters.
(3) Radio equipment that was made in America, either in whole or in part, has been found on several Japanese (0) Zero fighters (Zekes). Most parts are of Japanese manufacture, but components of German and English manufacture have been noted. Exact imitations of American and German designs also have been reported. There is no evidence of quantity production; indeed, all equipment noted is hand-made and of good construction. Good quality crystals are used in the majority of radios to control the frequencies of transmitters and receivers.
(4) Technical characteristics and photographs of airborne equipment are shown in figures 355 to 363.
3. TELEPHONES. a. Model 92 (1932) telephone (fig. 364). This telephone is of conventional design and normally is used on a ground return circuit, although it may be used also on a metallic circuit. It is equipped with a buzzer and key arrangement for sending code. The complete unit is encased in a metal-reinforced, wooden box, approximately 12 inches long, 5 inches wide, and 7 inches high. Directly beneath the aluminum cover is a transmitter, handset receiver, extra single earphone, and the buzzer key. Permanent lead-in wires are fitted to the telephone to which the field wire is attached. Current is supplied by a hand-cranked generator which generates ringing current rated at 55 volts A.C. It is not advisable, therefore, to use this set with U.S. Army generators which deliver up to 90 volts A.C. It will, however, receive and transmit clearly over U.S. Army circuits, being equipped with two 1 1/2 volt dry cell batteries which furnish 3 volts when connected in series. These batteries normally are connected in parallel and are stored on a metal rack inside the cabinet. Compared with Allied standards, the general mechanical construction of the set is inferior. It has been found that the hand-switch on the handset receiver causes frequent cut-outs as well as noise during operation. The set is contained in a heavy leather carrying case and may be carried easily by one man. A new carrying case, composed of layers of rubberized canvas, also has been observed. This material will withstand tropical climate much better than leather. The complete set weighs approximately 12 pounds.
b. Model 2 (1942) trench telephone (fig. 365). This telephone normally is used with a ground-return circuit, although it may be employed with a metallic circuit. The unit is contained in a wooden cabinet, with metal-reinforced corners. The handset; batteries; and generator, bell, condenser, and induction coil are housed in three compartments. The set may be operated on local or common battery circuits, while magneto signaling facilities also are included. The generator hand crank folds up and fits within the generator armature shaft. A fiber driving gear on the generator eliminates noise to some extent during cranking.
c. Sound-powered telephone (fig. 366). The microphone of the sound-powered telephone, deriving its energy directly from the sound waves, is a reversion to the original principle of the telephone in that the receiver unit is used also as a microphone. The instrument consists of a handset, with a single dual-purpose operating unit and an additional unit as an extra receiver. It is used to provide intercommunication within vehicles, or over short lines when circumstances require rapid and simple setting-up and disconnection.
d. Lip microphone. This carbon type microphone is attached to a leather and elastic strap. Total weight is approximately 3 1/2 ounces. Other than the fact that it is used with head receivers, there is nothing to indicate for what purpose it was intended. However, since the output of this microphone is low, it is possible that it may be used in connection with radio equipment in armored vehicles.
4. SWITCHBOARDS. The Japanese have field switchboards, but in place of these they frequently connect field telephones together to form a party line system. At higher headquarters and large airfields commercial switchboards and pole lines of open wire construction have been used.
5. TELEGRAPH SETS. Figure 367 illustrates the Model 95 set which can be used in conjunction with Model 92 telephone. The set has a built in key arrangement. It probably is used by lower units for administrative traffic.
6. SIGNAL LAMPS. a. Portable signal lamp. This lamp, provided with universal adjustment, is mounted on a tripod and powered by a hand generator. At the front, a hinged cover, equipped with a shutter adjustable to 6°, controls the intensity of light. A reflector and 6-volt lamp, rated approximately 32 candlepower, are contained inside the housing. Usually 3 different-colored filters—green, amber, and red—are provided with each lamp. A metal-reinforced wooden cabinet, 10 3/4 inches long, 5 3/8 inches high, and 8 3/8 inches wide, is provided for the equipment with the exception of the generator.
b. Hand signal lamp. This small pocket lamp measures 3 1/2 inches long. While resembling a cylindrical flashlight, it contains no batteries; instead, a cord, connected to an external battery, passes through the hollow wooden handle. The 3.5-volt bulb and reflector are of conventional design. Installed in front of the bulb is a glass filter, divided into red, blue, amber, and clear sectors. A cover, in front of the filter, can be revolved so that its opening will disclose a lighted segment of the desired color. Signaling is accomplished by a combination push button and slide switch on the side of the case. This lamp should be useful at short range, but the degree of security would be limited by the fact that its beam is not highly directional.
7. FIELD WIRE. The three principal types of field wire in general use are as follows:
a. Assault wire. Assault wire is very small in diameter. It consists of a single conductor and is composed of 8 strands (1 copper and 7 steel) with an outer covering of yellow-colored braid. This wire is for ground-return circuits and is used between regiments and forward units.
b. Seven-strand wire. This single conductor, 7-strand wire (3 copper and 4 steel) is larger in diameter than assault wire. The wire is rubber insulated, and tests have shown that the insulation resistance can remain high throughout a 14-day immersion period. It has an outer covering of yellow colored braid. Tensile strength of the wire is high, but its abrasion resistance is low, and its electrical characteristics are not as good as indicated by its construction. This wire is for ground-return circuits and is used between regimental and battalion headquarters.
c. Heavy wire. Heavy wire, consisting of two rubber-insulated, solid conductors (one black, the other red), is used for metallic circuits, probably between division and higher headquarters as well as at the larger airfields. It has an outer covering of green-colored braid.
8. CABLE. Different types of cables are used by the Japanese for various purposes. Figures 369 and 370 show types used and their characteristics.
9. WIRE REEL UNITS. The Japanese use various types of hand wire reel units, most of which appear to be designed primarily for handling single conductor wire.
a. Hand wire reel unit. The reel is carried on the shoulders, or to one side of the body, by means of a broomstick handle and it will hold approximately 1,600 feet of the larger diameter, yellow-braided, field wire. No crank is provided for convenient recovery of the wire. Perforations on the head and splines of the drum tend to damage the insulation if the wire is stored on the reel for any length of time. This unit, which is light in weight and not very rugged, can readily be dismantled without the use of tools. (See fig. 371.)
b. Head wire reel. The unit (see fig. 372) is solidly made of pressed metal, with leather straps for carrying on the chest or back. This reel evidently is designed for use by troops in forward areas and normally is carried on the back to allow free use of the hands. (See fig. 372.) When recovering wire, for which purpose a handle is provided, the reel normally is carried on the chest. The reel may be folded up when not in use.
10. AIRPLANE PANELS. Cloth air-ground panels are usually 1 1/2 to 3 feet wide and 6 1/2 to 13 feet long. Some shorter panels, and some triangular panels 3 to 6 1/2 feet on each side, have been used. In most cases panels are white, but other colors, contrasting to the terrain, also may be used. When regular panels are not available, rags, maps, or pieces of paper may be substituted. On occasion, Japanese soldiers have been observed to lie on the ground to form panel signals.
11. SIGNAL FLAGS. Two small hand flags, one red and the other white, are used for semaphore. For signaling Morse Code a large red and white flag, on a bamboo shaft about 5 feet long, is utilized.
12. MILITARY DOGS. Trained dogs, used to some extent for carrying messages, are cared for and trained by the division signal unit.
13. PIGEONS. Pigeons, also, are used for carrying messages.
14. HAND GENERATORS. a. Model "F". This simple and compact hand-driven generator, which weighs only 16 pounds, delivers 24 watts. It serves as a source of filament voltage (3 volts) and of plate voltage (125 volts). The mechanical transmission between driving handle and armature consists of 4 geared wheels, 2 of which are fiber, the others steel. According to the name plate, the normal rate of turning is 70 revolutions per minute, giving an armature speed of 5,200 revolutions per minute. Harness is provided for carrying the generator and for fastening it to a support. It is possible for a man to work the generator when the straps are slipped over his shoulders, with the base resting against his chest.
15. BATTERY CHARGER. Two charging circuits are provided. One uses a Tungar, half-wave rectifier, delivering 14 volts at 6 amperes. The other circuit uses a type 83, mercury-vapor, full-wave rectifier, delivering 130 to 160 volts at 0.1 ampere. Component parts are mounted on an angle-iron framework which fits into a metal carrying case. The case is provided with ventilating apertures, 3 weatherproof receptacles, a door at the rear, and a leather carrying handle. The charger is capable of charging one 12-volt storage battery and one storage "B" battery at an average efficiency of 30 percent. This efficiency compares favorably with that of half-wave Tungar chargers of American manufacture. The switching arrangement controlling the active turns in the transformer primaries allows operation of the charger from three different line voltages.
16. POWER UNITS—DUAL VOLTAGE DC (1300V/12V). This is a completely self-contained, rope-starting, power unit, consisting of a single cylinder of 1.977-inch bore x 2.0-inch stroke. The air-cooled gasoline engine is coupled directly to a straight-shunt, 2-pole-field, dual-voltage 1300V/12V generator, inclosed in an aluminum housing. Engine and generator are ruggedly constructed and supported, indicating long-life operation. This unit can be used to furnish plate voltage to U.S. Army SCR 177.
17. PYROTECHNIC SIGNALS. The Japanese make much use of pyrotechnic signals. Projection is achieved by means of Models 10 and 89 Grenade Dischargers, both of which are common infantry weapons.
Listed below are some of the pyrotechnic signals which can be used in grenade dischargers. They frequently have been referred to by the Japanese as dragons. The nature of the signal may be ascertained by two methods: (a) by color bands painted on the body, (b) by designs embossed on the cover (for use in the dark).
Signal pistol, 35-mm (1.38-inch) parachute and cluster "stars" in red, white, or green colors, with a burning time of from 4 to 15 seconds, are reported to exist. The cartridge closely resembles a shotgun shell. Model 97 (1937) signal pistol: One and three barrel models of this newer type signal pistol have been reported. The pistol is well made of a good grade of steel with an excellent finish: its overall length is 9 13/16 inches, and its weight is 1 pound 13 ounces.
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