B. Purpose -- relation to rest of RAD series
C. Radar Terms
D. Frequency bands
E. Radar nomenclature
The subject of radar is rather complex because of its technical nature and because it is still a new and rapidly growing field. A full appreciation of exactly how much radar can do and of how much it cannot do must therefore be based on an understanding of the many technical factors that influence radar operation. However, it has been attempted in this book to explain many of these considerations in relatively simple terms in order to make clear the capabilities and limitations of naval shipborne radar to personnel who have limited technical knowledge.
The purpose of RADONE-A is somewhat different from that of the original RADONE which it supersedes. All of the material on the tactical applications of radar has been removed, since RADFOUR, Air Plotting Manual, RADFIVE, Surface Plotting Manual, RADSIX, CIC Manual, RADEIGHT, Aircraft Control Manual, and RADNINE, Tactical Uses of Radar in Small Vessels, will contain this information in more complete and more modern form than was possible at the time that RADONE was prepared. RADTWO, The Tactical Use of Radar in Aircraft, is being modernized but it will retain approximately the same scope as the first edition. RADTHREE, Radar-Operator's Manual, describes the manipulation of controls and presents other data essential to the radar operator. RADSEVEN, which will be available some time in 1945, will be entitled Radar Countermeasures Manual. In addition to the foregoing, there are three other manuals in preparation for inclusion in the RAD series. They are to be: RADTEN, Airborne Radar Operator's Manual; RADELEVEN, Shipborne Radar Countermeasures Operator's Manual; and RADTWELVE, Airborne Radar Countermeasures Operator's Manual.
The purposes of the present edition of RADONE, then, are:
1. To describe the principles of operation of radar, IFF, beacons, and repeater indicators.
2. To furnish pertinent information about the characteristics and capabilities of radar, IFF, and beacons now in the fleet, and shortly to be available.
3. To explain the limitations imposed on the operation of radar, IFF, and beacons by: the properties of radio waves; uncontrollable factors, external to the equipment, such as the weather; inherent electrical and mechanical shortcomings of the equipment; operational difficulties; and enemy use of counter-measures.
It is expected that the material in this book will be of interest primarily to commanding officers, executive officers, and CIC Watch Officers in all ships of the Navy. However, much of the book will be of value not only to the radar operators, but also to all personnel who have an interest in the operational aspect of radar.
C. RADAR TERMS
Although radar has been in existence only a short time, a vocabulary of special terms has grown up with its development. As in any other art, it is difficult to gain a complete understanding of radar without first learning a few of the basic terms of its special language. Therefore, it is desirable to discuss a few terms that are frequently used before beginning explanation of radar. A fairly complete glossary of radar terms is included at the end of this book as Appendix A.
The unit of time most frequently used with radar is the microsecond. A microsecond is one-millionth of a second. It is abbreviated as μs or μsec, and generally used in calculation as 10-6 second.
A pulse is a sudden change of voltage or current of short duration; the pulse transmitted by a radar is produced by suddenly causing a normally quiescent circuit to generate radio-frequency energy during a very short interval of time. The pulse duration of the radar is the time during which the transmitter is actually generating radio-frequency energy in each cycle of operation. The number of pulses that are transmitted each second is called the pulse repetition rate, which is often abbreviated PRR. These quantities are indicated in figure 1A.
A radio-frequency pulse is a short burst of radio-frequency energy. The pulses transmitted and received
Figure 1--Radar pulses.
by the radar are radio-frequency pulses. The term video is borrowed from television, where it refers to the signals that produce the visible picture. A video pulse in radar is a similar signal. It is a unidirectional pulse--one in which the voltage does not alternate--that is derived from the receiver and used to produce the echo indication (fig. 1B).
The peak power of a radar is the power transmitted during the pulse. There is nothing transmitted during the resting time between pulses. Since the pulse duration is a very small fraction of the pulse repetition time, the average of the power transmitted over a complete cycle is small. However, the power transmitted during the pulse is large; peak power is measured in kilowatts or megawatts.
The device on which the echo signals are displayed in a radar system is a cathode-ray oscilloscope. The screen on which the echoes are viewed is usually called simply the scope. The time base on which the ranges of echoes are measured is produced by a current or voltage called a sweep.
The resolution of a radar is the separation between two targets required to permit the range, bearing, or altitude of either target to be determined with normal accuracy independently of the other target. Thus, range resolution is the minimum range difference between two targets that will allow the operator to obtain data on either of two targets on the same bearing. Bearing resolution is a similar quantity which expresses the minimum required bearing difference for two targets at the same range.
The electromagnetic field leaving a radar antenna varies continually in intensity because the current that produces it alternates at the frequency of the radar transmitter. This alternating field travels away from the antenna at the speed of light, producing a cyclic variation of the field intensity in space. The distance in which a complete cycle of the variation occurs is called the wavelength of the radio-frequency energy. The field intensities at two points a half-wavelength apart are equal in magnitude but they are always of opposite polarity, or 180° out of phase. In radar, wavelength is measured in meters or centimeters, and it is denoted by the Greek letter λ (lambda). Frequency and wavelength are used interchangeably in
radar, depending on which is the more convenient. They are related by the expression
λ = 300/f
in which λ is measured in meters, f is the frequency in megacycles, and the constant is the velocity of light in meters per microsecond.
D. FREQUENCY BANDS
If the exact frequencies on which all of the Navy's radars operate were widely known, the enemy would soon learn this very important information. This knowledge would simplify the development of effective countermeasures to our radar.
Therefore, five frequency bands denoted by code letters have been established. These five bands, in order of increasing frequency, are P, L, S, X, and K. Within each of these broad bands, relatively narrow frequency bands have been established for the operation of specific radar equipments. These narrow bands are denoted by a subscript letter on the basic letter, as Sw, for example. Radio frequencies may sometimes be indicated also by the system given below:
Very low frequency -- VLF 10 -- 30 Kilocycles Low frequency -- LF 30 -- 300 Kilocycles Medium frequency -- MF 300 -- 3000 Kilocycles High frequency -- HF 3 -- 30 Megacycles Very high frequency -- VHF 30 -- 300 Megacycles Ultra high frequency -- UHF 300 -- 3000 Megacycles Super high frequency -- SHF 3000 -- 30,000 Megacycles
Only the VHF, UHF, and SHF bands are used in radar. A third, and even more general, way of referring to the operating frequencies is to break them down into only two categories. Frequencies above approximately 600 megacycles per second, which have wavelengths shorter than 50 centimeters, are often referred to as microwave or centimeter wave. Wavelengths longer than 50 centimeters are called meter wave or long wave (for radar). Thus, the K, X, and S bands are microwave and the P band is long wave, but the L band covers the region between the two.
It is not important for either the operating or maintenance personnel to know the exact wavelength of a particular radar, beyond knowing the band in which it operates. In most equipment, test gear is
provided which is calibrated simply from 0 to 100, or with some such arbitrary scale. Since only relative measurements need be made on the equipment, such scales are entirely satisfactory, and they prevent the disclosure of the actual operating frequency to anyone--friend or enemy. Operating personnel should know the frequency band in which each set operates in order that they may realize the full capabilities of the equipment and understand the limitations imposed by the radio frequency transmitted. Neither the capabilities nor the limitations which are functions of frequency vary appreciably over a single band. However, there is a marked difference in the performance of an X-band radar compared to a P-band radar, for example.
E. RADAR NOMENCLATURE
The model designation of shipboard radar is intended to indicate in a general way the use to which the equipment is to be put. Except for fire control radar, which is given a "Mark" designation, the following letters are used to indicate application:
A--prefix indicating airborne installation.
For example, the SC, SK, SG, and SR are search radars. The second letter indicates approximately the order in which the equipment was developed. Improved models of a particular radar are designated by a letter or a number after the model designation, as SG-a, SG-1, and SG-3. The ABK is an airborne identification equipment, while the BK, BL, and BN are recognition equipments used on board ship. The YJ is a radar beacon, or racon, used to help airplanes to navigate back to a carrier or to a land base.
Airborne radar, beacons challenged by airplanes, radar countermeasures equipment, and other equipment used jointly by the Navy, Army, and Allied forces is designated by means of the AN nomenclature system. A chart explaining this system is given in Figure 2, and an article in the CIC Magazine for December, 1944 (Vol. I, No. 9) and in the Radio and Sound Bulletin, No. 17, January, 1945, may provide further explanation.
Comp. Ind. Family Name Definition or Example
Not to be construed as limiting the application of the component indicator to those items.
AB Antenna Supports Antenna mounts, mast bases, mast sections, towers, etc. AM Amplifiers Power, audio, interphone, radio frequency, panoramic, etc. AS Antenna Assemblies Complex: Arrays, parabolic type, masthead, etc. AT Antennae Simple: Whip or telescopic, loop, dipole, reflector, etc. BA Battery, primary type B-batteries, battery packs, etc. BB Battery, secondary type Storage batteries, battery packs, etc. BZ Audible Signal Devices Buzzers, gongs, horns, etc. C Control Articles Control box, remote tuning control, control unit, etc. CG R.F. Cables & Transmission Line R.F. cables, wave guides, etc., with terminals. CK Crystal Kits A kit of crystal units. CM Comparators Analyzes or compares two or more input signals. CN Compensators Electrical &/or mechanical compensating, regulating or attenuating apparatus. CP Computers A mechanical &/or electronic mathematical calculating unit. CR Crystal Units Crystal in crystal holder. CU Coupling Units Impedance coupling devices, directional couplers, etc. CV Converters (electronic) Electronic apparatus for changing the phase, frequency, or from one medium to another. CW Covers Cover, bag, roll, cap, radome, nacelle, etc. CX Cords Cord with terminals, also composite cables of R.F. and non-R.F. conductors. CY Cases Rigid and semi-rigid structure for housing or carrying equipment. DT Detecting Heads Magnetic pick-up device, search coil, etc. DY Dynamotors Dynamotor power units. F Filters Band-pass, noise, telephone, wave traps, etc. FN Furniture Chairs, desks, tables, etc. G Generators (See PU) Electrical power generators without prime movers. GO Goniometers Goniometers of all types. GP Ground Rods Ground rods, stakes, etc. H Head, Hand & Chest Sets Also includes earphone unit. HD Air Conditioning Apparatus Heating, cooling, dehumidifying, pressure units, vacuum units, etc. ID Indicators Azimuth, plan position-, elevation, panoramic, calibrated dials & meters, indicating light, etc. IL Insulators Strain, stand-off, feed-through, etc. J Junction Units Junction, jack & terminal boxes; connector panels, etc. KY Keying Devices Mechanical, electrical and electronic keyers, coders, interrupters, etc. LC Line Construction Tools Includes special apparatus such as cable plows, hoists, etc. LS Loudspeakers Separately housed loudspeakers. M Microphones Radio, telephone, throat, hand, etc. MD Modulators Device for varying amplitude, frequency or phase of alternating current. MK Maintenance Kits or Equipments Radio, telephone, general utility, etc. ML Meteorological Apparatus Barometer, hygrometer, thermometer, scales, etc. MT Mountings Mountings, racks, frames, stands, etc. MX Miscellaneous Equipment nut otherwise classified. O Oscillators Master frequency, blocking, multivibrators, etc. For test oscillators see TS. OA Operating Assemblies Operating units mounted together not otherwise covered. PF Pole Fittings Cable hanger, clamp, protectors, etc. PG Pigeon Articles Container, loft, vest, etc. PH Photographic Articles Camera, projector, sensitometer, etc. PP Power Supplies Non-rotating machine type such as vibrator pack, rectifier, thermoelectric, etc. PT Plotting Equipments Except meteorological. Boards, maps, plotting table, etc. PU Power Equipments Rotating power equipment except dynamotors. Electric motors, combustion type engines, etc. R Radio & Radar Receivers Radio or radar receiver, combined unit such as Receiver-Indicator, etc. RD Recorders & Reproducers Tape, facsimile, disc, magnetic, etc. RE Relay Assemblies Electric, electronic, etc. RF Radio Frequency Units Miscellaneous radio frequency apparatus. RG Bulk R.F. Cables & Transmission Line R.F. cable, wave guides, etc., without terminals. RL Reel Assemblies Antenna, field wire, etc. RP Rope & Twine Non-electrical cord, etc. RR Reflectors Target, confusion, etc. Except antenna reflectors. (Sec AT.) RT Receiver and Transmitter Radio and radar transceivers, transmitter and receiver in one unit, etc. S Shelters House, tent, protective shelter, etc. SA Switching Assemblies Manual, impact, motor driven, pressure operated, etc. SB Switchboards Telephone, fire control, power, panel, etc. SM Simulators Flight, aircraft, target, signal, etc. SN Synchronizers Equipment to coordinate two or more functions. ST Straps Harness, straps, etc. T Radio & Radar Transmitters Communications, range, marker beacon, interrogator, combined Transmitter-Modulator, etc. TA Telephone Apparatus Miscellaneous telephone equipment. TD Timing Devices Mechanical and electronic timing devices, etc. TF Transformers Transformers when used as separate units. TH Telegraph Apparatus Miscellaneous telegraph apparatus. TK Tool Kits or Equipments Miscellaneous tool assemblies. TL Tools All types except line construction. TN Tuning Units Receiver, transmitter, antenna, etc. TS Test Equipments Test and measuring equipment including dummy antenna, pick-up probes, etc. TT Teletypewriter & Facsimile Apparatus Miscellaneous tape, teletype, facsimile equipment, etc. U Audio & Power Connectors Unions, plugs, sockets, adapters, etc. UG R.F. Connectors Unions, plugs, sockets, choke couplings, adapters, elbows, flanges, etc. V Vehicles Carts, dollies, trucks, trailers, etc. VS Visual Signaling Equipments Flag sets, aerial panels, signal lamp equipment, etc. WD Two Conductor Cables Includes non-R.F. wire, cable & cordage in bulk. WF Four Conductor Cables Includes non-R.F. wire, cable & cordage in bulk. WM Multiple Conductor Cables Includes non-R.F. wire, cable & cordage in bulk. WS Single Conductor Cables Includes non-R.F. wire, cable & cordage in bulk. WT Three Conductor Cables Includes non-R.F. wire, cable & cordage in bulk.
Figure 2--Summary of Joint Army-Navy Nomenclature System ("AN" System) for Communication and Associated Equipment.
Installation Type of Equipment Purpose A--airborne (installed & operated in aircraft) B--pigeon A--auxiliary assemblies (not complete operating sets) C--carrier (wire) C--air transportable (designed to be air transportable as stated in specification or military characteristics) F--photographic G--telegraph or teletype (wire) C--communications (receiving & transmitting) I--interphone & public address F--ground, fixed D---direction finder G--ground, general ground use (includes two or more ground installations) M--meteorological G--gun directing N--sound L--searchlight control P--radar M--maintenance and test assemblies (including tools) R--radio M--ground, mobile (installed as operating unit in a vehicle which has no function other than transporting the equipment) S--special types (heat, magnetic, etc.) or combination of types N--navigational aids (including altimeters, beacons, compass & instrument landing) T--telephone (wire) P--ground, pack or portable (horse or man) V--visual and light S--shipboard X--facsimile or television Q--special, or combination of types V--ground, vehicular (installed in vehicle designed for functions other than carrying radio equipment, etc., such as tanks) R--receiving S--search &/or detecting T--transmitting W--remote control T--ground, transportable X--identification & recognition U--general utility (includes two or more general installation classes, airborne, shipboard & ground)
EXAMPLES OF AN TYPE NUMBERS Type Number Indicates AN/FRC-1() General reference set nomenclature of fixed ground radio communications set No. 1 AN/CRC-3 Air transportable radio communications set No. 3 AN/MPS-2 (XE-1) Camp Evans Signal Laboratory developmental model No. 1 of ground mobile radar search set No. 2 AN/APS-3-T1 Training set No. 1 for airborne radar search set No. 3 T-780/SPT-6 General reference component nomenclature for radar transmitter No. 78, part of or used with shipboard radar transmitting set No. 6 R-75/CRW-2A Radio receiver No. 75, part of or used with air transportable radio remote control set No. 2A TK-5/FR Tool kit No. 5 for fixed ground radio equipment, not part of a specific set
1. The system indicator "AN" does not mean that both the Army and Navy use the equipment, but simply that the type number was assigned in the AN System.
2. In the AN Nomenclature System, nomenclature consists of a name followed by a type number. The name will be terminology of standard engineering usage. The type number will consist of indicator letters shown on this chart and an assigned number.
3. Modification letters will be assigned for each modification when parts are no longer interchangeable. Different numbers will be assigned to components not electrically and mechanically interchangeable as a whole. The component will retain its original nomenclature even though later made part of other equipment.
4. The type number of an independent major unit, not part of or used with a specific set, will consist of a component indicator, a number, the slant, and such of the set or equipment indicator letters as apply. Example: SB-5/PT would be the type number of a portable telephone switchboard for independent use.
5. IMPORTANT: All personnel are cautioned against originating or changing any part of any nomenclature assignment, including modification letters, without authorization.
Modification letters will be assigned for each modification not affecting interchangeability of the sets or equipments as a whole, except that in some special cases they will be assigned to indicate functional interchangeability and not necessarily complete electrical and mechanical interchangeability.
The suffix letters X, Y and Z will be used only to designate a set or equipment modified by changing the input voltage, phase or frequency. X will indicate the first change, Y the second, Z the third, XX the fourth, etc., and these letters will be in addition to other modification letters applicable.
Experimental Sets. In order to identify a set or equipment of an experimental nature with the development organization concerned, the following indicators will be used within the parentheses:
XA--Aircraft Radio Laboratory
XC--Camp Coles Signal Laboratory
XE--Camp Evans Signal Laboratory
XM--Fort Monmouth Signal Laboratory
XO--Eatontown Signal Laboratory
XP--Army Pictorial Service
XT--Toms River Signal Laboratory
Example: Radio Set AN/ARC-3 () might be assigned for a new airborne radio communication set under development. The cognizant development organization might then assign AN/ARC-3 (XA-1), AN/ARC-3 (XA-2), etc., type numbers to the various sets developed for test. When the set was considered satisfactory for use, the experimental indicator would be dropped and procurement nomenclature AN/ARC-3 would be assigned thereto.
Training Sets: A set or equipment designed for training purposes will be assigned type numbers as follows:
1. A set to train for a specific basic set will be assigned the basic set type number followed by a dash, the letter T, and a number. Example: Radio Training Set AN/ARC-6A-T1 would be the first training set for Radio Set AN/ARC-6A.
2. A set to train for general types of sets will be assigned the usual set indicator letters followed by a dash, the letter T, and a number. Example: Radio Training Set AN/ARC-T1 would be the first training set lor general airborne radio communication sets.
Parentheses Indicator. A nomenclature assignment with parentheses, ( ), following the basic type number is made to identify an article generally, when a need exists for a more general identification than that provided by nomenclature assigned to specific designs of the article. Example: AN/GRC-5(), AM-6()/GRC-5, SB-9()/GG. A specific design is identified by the plain basic type number, the basic type number with a suffix letter, or the basic type number with an experimental symbol in parentheses. Examples: AN/GRC-5, AN/GRC-5A, AN/GRC-5 (XC-1), AM-6B/GRC 5, SB-9 (XO-3)/GG.
Modifications After Production. If an article, either a set or a component, is modified after production, the modified article may be identified by the addition of the suffix letter "M" to the original type number. For example, MD-75/GR becomes MD-75M/GR, and AN/ARC-5 becomes AN/ARC-5M. Subsequent modifications for which similar identification is desired will be assigned with a numerical suffix to the M. Subsequent factory productions identical to the modified articles will be identified the same as the modified articles.
1. AN Nomenclature will be assigned to:
a. Complete sets of equipment and major components of military design.
b. Groups of articles, of either commercial or military design, which are grouped for a military purpose.
c. Major articles of military design which are not part of or used with a set.
d. Commercial articles when nomenclature will facilitate military identification and/or procedures.
2. AN Nomenclature will not be assigned to:
a. Articles cataloged commercially, except in accordance with Paragraph 1.d.
b. Minor components of military design for which other adequate means of identification are available.
c. Small parts such as capacitors and resistors.
d. Articles having other adequate identification in American War Standard or Joint Army-Navy Specifications.
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