The rf tuning unit consists of variable oil-filled capacitors and a fixed inductor for frequency tuning. The signal is then sent to a knife switch. This switch simply routes the signal to the DUMMY LOAD or the antenna by way of the HELIX HOUSE. (A dummy load is a nonradiating device the absorbs the rf
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and has the impedance characteristics of the antenna.) The dummy load is impedance matched to the pa. It allows testing of the pa without putting a signal on the air. When the equipment is in an operating mode, the dummy load is not used. The helix house is a small building physically separated from the transmitter location. It contains antenna loading, coupling, and tuning circuits. The main components consist of a HELIX (large coil) and variable inductors. The signal is fed from the helix directly to the antenna. Sometimes two antennas are used.
Antenna designs vary with the amount and type of land available, desired signal coverage, and bandwidth requirements. Figure 5-2 shows a simplified transmit antenna. The Navy uses TOP-HAT (flat- top) capacitive loading with one or more radiating elements. Typical top hat antennas consist of two or more lengths of wire parallel to each other and to the ground, each fed at or near its mid point. The lengths of wire are usually supported by vertical towers. These antennas may take many shapes. The matching network shown is in the helix house. Figure 5-3 shows the installation at the naval communications unit in Cutler, Maine. The Navy has several of these types of installations. They are used primarily for fleet broadcasts and have power outputs in the .25- to 2-megahertz range. You should notice the transmitter, the location of the helix houses, and the dual antennas. You should also notice the transmission line tunnel. It is underground and over a half-mile long. Figure 5-4, view (A) and view (B), shows another antenna configuration. This array of monopoles (quarter-wave, vertically polarized stubs) is referred to as a TRIATIC antenna. A triatic antenna is a special form of a rhombic-arranged monopole array. This type of array is designed to transmit from a particular location. Triatics are all basically the same but have some design differences at each site. The physical differences compensate for differences in terrain. Now that we have looked at the transmit side, let's look at the receive side.
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The receiver you will study here is fundamentally the same as those we covered in chapter 2. A receiver used in this frequency range is about the same electrically as one used in any other range. Figure 5-5 shows the receiver we will discuss. It is a highly sensitive, special purpose receiver because it is capable of splitting-out multiplex signals for detection and reproduction. This receiver covers the frequency range of 3 kilohertz to 810 kilohertz in five bands. It will receive most types of signals, including AM, cw, ssb, fm, and fsk. All operator controls are on the front panel, and a speaker and headset jack permit monitoring.
Our receiver has five basic stages excluding the power supply.  Figure 5-6 is a block diagram showing the signal paths of the receiver. The input stage consists of a low-pass filter, an attenuator, a calibration oscillator, and a video amplifier. The low-pass filter passes input frequencies below 900 kilohertz. These frequencies are passed to the attenuator, which sets the signal to the proper level to drive the mixer. This minimizes noise and distortion. The calibration oscillator produces a 250-kilohertz output. It is used to calibrate the receiver level and to check for tuning dial accuracy. The input signal is direct-coupled from the attenuator to the video amplifier. This amplifier is a broadband, constant-impedance driver for the mixer. The oscillator-mixer stage consists of a mixer, phase splitter, local oscillator, and frequency control circuits.
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A Hartley configuration is used for the local oscillator. The oscillator output is equal to the tuned frequency plus 2.215 megahertz. Two voltage-variable capacitors are used in the local oscillator to stabilize small frequency variations. A phase splitter is used to drive the mixer diodes into conduction during half of the local oscillator cycle.
The mixer circuit uses the diodes to heterodyne the input signal with the local oscillator signal from the phase splitter. The diodes short the signal to ground during half the local oscillator cycle.
The IF amplifier stages consist of the mixer amplifier, four selectable bandwidth filters, three IF amplifiers, and an IF buffer amplifier.
The output of the mixer is directly coupled to the mixer amplifier. The IF signal is then directed through one of four bandwidth filters to the first IF amplifier. The signal proceeds to the second and third IF amplifiers for amplification before demodulation. An IF buffer amplifier is used to pass the IF to the IF OUT jack and to isolate this jack from the rest of the circuitry.
Three demodulators are used in this receiver. They are the AM detector, product detector, and fm detector. The AM detector is used to demodulate AM signals. The product detector demodulates ssb, cw, and fsk signals, and the fm detector demodulates fm signals only. An output from the fm detector is provided to the FM OUT jack. This fm output may be used for recording or detailed analysis.
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The output from the selected demodulator is amplified by the audio amplifier and presented simultaneously to the HEADSET jack, AUDIO OUT terminals, and the speaker.
You should note that this receiver, as with most others, requires no other special equipment. It uses a standard df loop or a whip antenna. If it is installed in a submarine, a trailed, (towed) long-wire antenna may be used.
Communications systems in the 1 gigahertz to 10 gigahertz portion of the radio frequency spectrum use line-of-sight propagation. Propagation takes place in the lower atmosphere (troposphere). It is affected by factors such as barometric pressure, temperature, water vapor, turbulence, and stratification (forming of atmospheric layers).
A typical microwave transmitter includes an exciter group, a modulator group, a power amplifier, and power supplies. The transmitter usually has a power output of about 1 watt. When a higher output is required (about 5 watts), a traveling-wave tube (twt) is used as the amplifier. (A twt is a high-gain, low- noise, wide-bandwidth microwave amplifier. It is capable of gains of 40 decibels or more, with bandwidths of over an octave. The twt was discussed in chapter 2 of NEETS, Module 11, Microwave Principles.) A typical microwave receiver contains an rf-IF group, local oscillator, demodulator, and amplifier. Both transmitters and receivers contain special circuits because of the high operating frequencies and critical frequency stability requirements.
A line-of-sight (los) microwave system consists of one or more point-to-point hops as shown in figure 5-7. Each hop is designed so that it can be integrated into a worldwide communications network. Los systems have many characteristics. In these systems, propagation is only affected by changes in the troposphere. The distance between microwave system hop points ranges from 50 to 150 kilometers (31 to 95 statute miles). These systems are capable of handling up to 600 4-kilohertz voice channels and can also transmit television. These signals can usually be transmitted with less than 10 watts of power. Both the transmit and receive antennas are horn-driven paraboloids that provide high gain and narrow beam widths. In some applications, as shown in figure 5-8, plane reflectors are used with the paraboloids. These systems are very reliable. They are designed to operate over 99 percent of the time. These systems are well adapted to multichannel communications and closed circuit television.
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Now let us take a look at another system. It is called the tropospheric-scatter microwave system. But first, you may want to review tropospheric propagation in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas.
A tropospheric-scatter (tropo-scatter) microwave system gets results similar to those of the line-of- sight system. It does it in a different way. The los system uses towers to relay information.
The tropo system uses the turbulence in the layer between the troposphere and the stratosphere to bounce signals back to earth. This method provides several hops and communications beyond los. The propagation reliability and communications capability is the same. The transmission range is up to 800 kilometers (500 statute miles). Transmitter output power may be up to 75 kilowatts depending on the operational requirements. The antennas are horn-driven paraboloids and may be as large as 50 to 60 feet in diameter. Figure 5-9 shows a typical tropospheric-scanner antenna. Remember that hf has a hop distance (skywave) of about 1,400 miles; the distance of one hop for a line-of-sight system is between 31 and 95 miles. The tropospheric-scatter system conveniently fills the gap between these distances.
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Both of these systems are used ashore. You're now going to get a look at a shipboard data information exchange system.
Q1. What is a dummy load?
Q2. What is the function of a product detector?
Q3. What is the frequency range of the mf band?
Q4. Microwave systems use what portion of the atmosphere?
Q5. What is the voice channel capacity of an los communications system?
Q6. What is the one-hop transmission range of a tropospheric-scatter system?
In recent years, the Navy has introduced several new highly technical and effective combat weapons systems. However, these weapons systems did not solve the basic combat command problems that confront our Navy. In combat, a fleet continues to be involved in close-range offense and defense. During close-range combat, the shipboard combat information center (CIC) is involved in complex tactical situations. These situations require intelligent and highly important decisions. Each decision has to be made in a short period of time. You will find the speed at which these combat situations must be solved is inconceivable to someone thinking in terms of typical CIC operations of the recent past. Therefore, the NTDS was developed by the U.S. Navy as a command tool for commanders in tactical combat situations.
The naval tactical data system (NTDS) is based on the interaction of humans and machines. The NTDS helps coordinate fleet air defense, antisubmarine warfare, and surface defense operations. Through
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automation, the NTDS provides commanders with a broad picture of the current tactical situation. It also assists them in directing their operations in time to intercept and destroy all potential enemy threats. The use of digital computers and digital data processing techniques reduces reaction time and increases force effectiveness.
NTDS uses a variety of equipment. This equipment includes transmitters, receivers, cryptographic equipment, high-speed digital computers, magnetic tapes, disks, and a variety of displays. Figure 5-10 shows the NTDS equipment grouping and how it interfaces with the weapons and sensor systems of a ship. Figure 5-11 shows the NTDS system inputs and outputs. As you can see, large amounts and various types of information are provided to or taken from the NTDS. Now that you have seen the types of information associated with the NTDS, let's look at how this information is transmitted and used.
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NTDS uses three separate data transmission links to maintain tactical data communications between tactical units. Figure 5-12 illustrates these links. Each link is able to transfer data rapidly to other ships, aircraft, and shore facilities without the delay of human interface (link 14 receive is an exception to this). The data processing subsystem formats the messages for each of the data links. These messages are based on shipboard inputs (from displays, sensors, and other data links).
The automatic data communications links provide the operational commander with a high-speed, accurate mode of tactical communications. Link 11 provides high-speed, computer-to-computer transfer of tactical information, command orders, and unit status to all tactical data systems. View A shows you this configuration. The type of tactical information currently transferred is surface, subsurface, air, and EW track information. Data is provided on friendly, hostile, and unknown identity tracks. This broadcast originates through console button actions by the console operators.
Link 14 provides a means of transmitting track information to those units not capable of participating in the link 11 network. View B shows this network. This is a one-way broadcast of information.
Link 4A permits the computer to take control of the autopilot in an equipped aircraft. Also this link can control a plane under other situations. It may control a flight out to a strike area and return it to base without the need for pilot action. The pilot also has the option of overriding the link. The pilot may use the visual display to aid in understanding the intercept controller, or to totally ignore the link 4A
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transmission. View C shows this link used in conjunction with the automatic carrier landing system (ACLS).
Figure 5-13 is a drawing of an intersystem communications employment diagram. It shows the overall possibilities and flexibility of the NTDS. The new terms shown are defined below:
Now that we've looked at a complex and stationary system, let's study some fundamental portable equipment.
Q7. What is the primary advantage of NTDS over conventional systems?
Q8. What are the three NTDS data transmission subsystems?
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Portable and pack radio sets must be lightweight, compact, and self-contained. Usually, these sets are powered by a battery or a hand generator, have low output power, and are either transceivers or transmitter-receivers. A transceiver consists of a transmitter and a receiver that share common circuits and are housed in the same case or cabinet. A transmitter-receiver is the combination of two separate pieces of equipment that are used together. Navy ships carry a variety of these radio sets for emergency and amphibious communications. The numbers and types of equipment vary according to the individual ship.
One piece of emergency equipment is shown in figure 5-14. It is a rugged emergency transmitter carried aboard ships and aircraft for use in lifeboats and life rafts. The transmitter operates on the international distress frequency (500 kilohertz) and the survival craft communications frequency (8,364 kilohertz).
The complete radio transmitter, including the power supply, is contained in an aluminum cabinet that is airtight and waterproof. The cabinet is shaped to fit between the legs of the operator and has a strap for securing it in the operating position.
The only operating controls are a three-position selector switch and a push-button telegraph key. A hand crank screws into a socket in the top of the cabinet. The generator, automatic keying, and automatic frequency changing are all operated by turning the hand crank. While the hand crank is being turned, the set automatically transmits the distress signal SOS in Morse code. The code consists of six groups of SOS followed by a 20-second dash. It is transmitted alternately on 500 kilohertz and 8,364 kilohertz. The frequency automatically changes every 50 seconds. These signals are intended for reception by two groups of stations, each having distinct rescue functions. Direction-finding stations cooperating in long- range rescue operations normally use 8,364 kilohertz, whereas aircraft or ships locally engaged in search and rescue missions use 500 kilohertz.
Besides the automatic feature, you can key the transmitter manually on 500 kilohertz only. This is done by means of a push-button telegraph key.
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Additional items (not shown) packaged with the transmitter include the antenna, a box kite, and balloons for supporting the antenna. Hydrogen-generating chemicals for inflating the balloon and a signal lamp that can be powered by the hand-crank generator are also included.
The equipment floats and is painted brilliant orange-yellow to provide good visibility against dark backgrounds.
A transceiver is shown in figure 5-15. It is portable, battery powered, and has two channels. It provides homing information and two-way voice communications between life rafts and searching ships and aircraft. This transceiver is a microminiature, solid-state, hand-held radio that operates on the 121.5-megahertz and the 243-megahertz guard channels. The transceiver has four operating controls. These are the volume (VOL) control, the two-position FREQUENCY SELECTOR, the PUSH-TO- TALK/ CODE button, and the three-position MODE switch.
The antenna is a rubber covered, omnidirectional, flexible whip antenna that is 7.74 inches long. The batteries supplied with the radio set are lithium D cells. Each cell is fused to protect against damage from external short circuits. Two cells are installed in the transceiver and four are packaged as spares.
An operational transceiver is shown in figure 5-16. It is watertight, lightweight, portable, and operates in the vhf and uhf range. You can use any of 1,750 channels, spaced 200 kilohertz apart, in the 225-400 megahertz range. Its mode of operation is AM voice and it supplies an average output power of 3 watts. It was designed mainly for manpack (backpack) use, but it may also be used at a fixed station or in vehicles when certain accessories are added. When not in use, the equipment is disassembled and stowed in a special aluminum case similar to an ordinary suitcase.
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Figure 5-17 shows a typical vhf miniaturized manpack radio set. View A shows the pack frame, the handset, and the canvas accessory pouch. The pouch contains two antennas (one flexible steel band-type whip and one collapsible rigid whip). The handset fits in the pouch when not in use. View B shows the transmitter-receiver.
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Now that you have learned about portable equipment, let's look at one of the newest areas of communications. You are going to learn the fundamentals of how a laser works and how it may be used in the field of communications.
Q9. What are the three main design considerations of portable equipment?
The word LASER is an acronym for light amplification by stimulated emission of radiation. The laser is widely used in industry, and experimental work is being done with it in communications. You will find a laser is similar to uhf and microwave power sources and could replace either of them in point-to- point communications.
Lasers take energy at (or near) the visible light spectrum and convert it to a very narrow and intense beam in the same region. A close relative of the laser is the light emitting diode (LED). The LED takes dc or low frequency ac power and converts the energy into visible light.
The principle of the laser is somewhat similar to that of a very high-Q cavity resonator. Chapter 1 of NEETS, Module 11, Microwave Principles, explains cavity resonators. The laser is shock-excited by a spark transmitter. This transmitter is called a spark transmitter because it uses the discharge of a capacitor through an inductor and a spark gap as a source of rf. While the input energy of the laser covers a wide band of frequencies, the output is on one frequency. Energy outputs of the laser are either INCOHERENT or COHERENT. For example, if you turn on a transmitter with no modulation, you will get coherent radiation. When you connect a noise source to an antenna, the result is incoherent radiation.
Lasers can be either cw or pulsed. Actually, lasers are little different from conventional oscillators. However, the way lasers convert energy from one form to another is quite different. In conventional oscillators, dc power from the collector is converted to rf energy. The frequency is for the most part independent of the molecular or atomic structure of the generator. This is not true for the laser. Laser conversion takes place directly within the molecular structure of a crystal or gas. The external circuits have little effect on actual output frequency. The fact that the light from an LED is always the same color results from similar conditions. In a laser, incoherent light excites the electrons in the atoms to higher energy levels than they normally would have. The new energy states are unstable and the electrons drop down to lower energy levels. Energy is then released in the form of light.
Figure 5-18 shows the ends of the crystal or glass tube laser with light waves reflecting back and forth between two mirrored surfaces. One mirror is only partially reflective, and light energy is transmitted through it to form the light beam. You will find that power sources for lasers include flash tubes or, in the case of diode-type lasers, dc power supplies.
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High-energy lasers have very small power losses. As a result, a laser with a 2- or 3-inch initial beam can be used to communicate directly with a distant planet. However, from a communications standpoint, they do have some drawbacks. While laser energy is capable of being formed into a very narrow beam, it is still subject to the same difficulties as any other form of light transmission. Fog and other adverse weather conditions can absorb the light. Small atmospheric temperature variations can cause deflection and scattering. An optical waveguide was designed to help overcome this problem. It consists of a thin dielectric fiber clothed by another dielectric coating several wavelengths thick. It has been successfully used to move the beam over considerable distances and around bends. The use of optical waveguides is known as FIBER OPTICS. A number of fibers can be paralleled to reduce the attenuation through the waveguide. This technique has resulted in an inexpensive telephone system with a bandwidth greater than that of previous methods. Researchers are attempting to develop a laser that will operate in the blue-green portion of the visible spectrum. Water offers little attenuation to the blue-green band of frequencies. Because of this, blue-green communications lasers could possibly penetrate the ocean to great depths.
This could give us a very secure undersea communications link.
Q10. Lasers operate in what portion of the frequency spectrum?
Q11. What are the two types of lasers?
Q12. What are the effects of adverse weather on the laser beam?
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Now that you have completed this chapter, a review of what you have learned is in order. The following summary will refresh your memory of new terms.
DOUBLING UP is a type of two-equipment installation where one unit can be substituted for another in the event of failure.
FREQUENCY SYNTHESIZER is a frequency source of high accuracy.
DUMMY LOAD is a nonradiating device that absorbs the rf and has the impedance characteristics of the antenna.
HELIX HOUSE is a building at a transmitter site that contains antenna loading, coupling, and tuning circuits.
A HELIX is a large coil of wire. It acts as a coil and is used with variable inductors for impedance matching of high-power transmitters.
TOP-HAT antennas are center-fed and capacitively loaded.
TRIATIC is a special type of monopole antenna array.
LASER is an acronym for light amplification by stimulated emission of radiation.
COHERENT refers to radiation on one frequency or nearly so.
INCOHERENT refers to radiation on a broad band of frequencies.
FIBER OPTICS are conductors or optical waveguides that readily pass light.
MTDS is an abbreviation for the marine tactical data system.
AFDS is an abbreviation for the amphibious flagship data system.
ATDS is an abbreviation for the airborne tactical data system.
ASWTDS is an abbreviation for the antisubmarine warfare tactical data system.
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ANSWERS TO QUESTIONS Q1. THROUGH Q12.
A1. An impedance-matched device capable of absorbing all of a transmitters power.
A2. It demodulates ssb, cw, and fsk signals.
A3. 300 kilohertz to 3 megahertz.
A4. Troposphere.
A5. Up to 600 4-kilohertz channels.
A6. Up to 800 kilometers (500 statute miles).
A7. Speed.
A8. Links 4A, 11, and 14.
A9. They must be lightweight, compact, and self-contained.
A10. At or near visible light.
A11. Cw or pulsed.
A12. It absorbs it.
AI-1
ACTIVE SATELLITE—A satellite that amplifies the received signal and retransmits it back to earth.
AFDS—An abbreviation for the amphibious flagship data system.
ANGLE OF INCLINATION—The angular difference between the equatorial plane of the earth and the plane of orbit of the satellite.
ANTENNA COUPLER—A device used for impedance matching between an antenna and a transmitter or receiver.
APOGEE—The point in the orbit of a satellite the greatest distance from the earth.
ASSEMBLY—A number of parts or subassemblies, or any combination thereof, joined together to perform a specific function.
ASWTDS—An abbreviation for the antisubmarine warfare tactical data system.
ASYNCHRONOUS ORBIT—One where the satellite does not rotate or move at the same speed as the earth.
ATDS—An abbreviation for the airborne tactical data system.
AUDIO FREQUENCY TONE SHIFT—A system that uses amplitude modulation to change dc mark and space impulses into audio impulses.
AUTOMATIC TRACKING—Tracking done by the equipment comparing the direction of the antenna axis and the direction of the received signal.
AUTOMATIC VOLUME/GAIN CONTROL—A circuit used to limit variations in the output signal strength of a receiver.
BALANCED PHASE DETECTOR—A circuit that controls the oscillator frequency (afc). BAUD—A measurement of speed based on the number of code elements or units per second.
BEAT-FREQUENCY OSCILLATOR—An additional oscillator used in a receiver when receiving a cw signal. It provides an audible tone.
BITS-PER-SECOND—Bit is an acronym of the words binary digit. One bit is equal to one signal unit or element.
BLACK—The reference color of equipment that passes unclassified information. It normally refers to patch panels.
CODE—In teletypewriter operation, code is a combination of mark and space conditions representing symbols, figures, or letters.
COHERENT—Radiation on one frequency.
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COMPARATOR—An equipment that compares incoming signals and selects the strongest to be fed to a teletypewriter through a patch panel. This is used in diversity operation.
CONVERTER—An equipment that changes the audio output of a receiver to dc pulses. These pulses are fed to a tty to indicate marks and spaces.
DETECTION—The separation of low-frequency (audio) intelligence from the high (radio) frequency carrier.
DOUBLING UP—This is a type of two-equipment installation where one unit can be substituted for another in the event of failure.
DOWN LINK—The frequency used to transmit an amplified signal from the satellite back to earth.
DUMMY LOAD—A nonradiating device that absorbs the rf and has the impedance characteristics of the antenna.
ECLIPSE—This occurs when the satellite is not in view or in direct line of sight with the sun. This happens when the earth is between them.
ELECTROMAGNETIC INTERFERENCE—A term used to describe the degradation of a receiver or system.
EPHEMERIS—A table showing the precalculated position of a satellite at any given time.
EQUATORIAL ORBIT—An orbit that occurs when the plane of a satellite coincides with the plane of the earth at the equator.
EXTREMELY HIGH FREQUENCY—The band of frequencies from 30 gigahertz to 300 gigahertz. EXTREMELY LOW FREQUENCY—The band of frequencies up to 300 hertz. FACSIMILE—The method for transmitting and receiving still images. These images can be maps,
photographs, and handwritten or printed text.
FADING—The variations in signal strength at the antenna of a receiver.
FIBER OPTICS—Conductors or optical waveguides that readily pass light.
FIDELITY—The ability of a receiver to accurately reproduce, at its output, the signal at its input.
FORWARD AGC—The type of agc that causes an amplifier to be driven towards saturation.
FRAMING—The process of synchronizing a facsimile receiver to a transmitter. This allows proper picture reproduction.
FREQUENCY-DIVISION MULTIPLEXING—Multiplexing that transmits and receives the full 360 degrees of each sine wave.
FREQUENCY SYNTHESIS—A process that uses hetrodyning and frequency selection to produce a signal.
FREQUENCY SYNTHESIZER—A frequency source of high accuracy. GANGED TUNING—The process used to tune two or more circuits with a single control.
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GROUP—A collection of units, assemblies, subassemblies, and parts. It is a subdivision of a set or system but is not capable of performing a complete operational function.
HAND OVER—The operation where one earth terminal yields control to another as a satellite moves out of its area of coverage.
HARMONIC—An exact multiple of the fundamental frequency. Even harmonics are 2, 4, and so on, times the fundamental. Odd are 3, 5, and so on, times the fundamental frequency.
HELIX—A large coil of wire. It acts as a coil and is used with variable inductors for impedance matching of high-power transmitters.
HELIX HOUSE—A building at a transmitter site that contains antenna loading, coupling, and tuning circuits.
HETERODYNING—The mixing of the incoming signal with the local oscillator frequency. This produces the two fundamentals and the sum and difference frequencies.
HIGH FREQUENCY—The band of frequencies from 3 megahertz to 30 megahertz. IMAGE FREQUENCY—An undesired frequency capable of producing the desired frequency through
heterodyning.
INCLINED ORBIT—Orbits where there is some amount of inclination. These include equatorial and polar orbits.
INCOHERENT—This refers to radiation on a broad band of frequencies.
INTELLIGENCE—Any signal that conveys information (voice, teletypewriter, facsimile). KEYER—A device that changes dc pulses to mark and space modulation for teletypewriter
transmissions.
LASER—An acronym for light amplification by stimulated emission of radiation.
LISSAJOUS PATTERN—A combined, simultaneous display of the amplitude and phase relationships of two input signals on a CRT.
LOW FREQUENCY—The band of frequencies from 30 kilohertz to 300 kilohertz. MARKING—The state where a circuit is closed and current flows in teletypewriter operation.
MEDIUM ALTITUDE ORBIT—An orbit from 2,000 to 12,000 miles above the earth. The rotation rate of the earth and satellite are quite different, and the satellite moves quickly across the sky.
MEDIUM FREQUENCY—The band of frequencies from 300 kilohertz to 3 megahertz. MTDS—An abbreviation for the marine tactical data system.
MULTICOUPLERS—Couplers patch receivers or transmitters to antennas. They also filter out harmonics and spurious responses, and impedance-match the equipment.
MULTIPLEXING—A method for simultaneous transmission of two or more signals over a common carrier wave.
AI-4
NEAR SYNCHRONOUS ORBIT—An orbit in which the satellite rotates close to but not exactly at the same speed as the earth.
NEUTRAL—The teletypewriter operation where current flow represents a mark and no flow represents a space.
NOISE SILENCER, NOISE SUPPRESSOR, OR NOISE LIMITER—Circuits that clip the peaks of the noise spikes in a receiver.
ORDER-WIRE CIRCUIT—A circuit between operators used for operations control and coordination.
PAGE PRINTER—A high-speed printer that prints teletypewriter characters one at a time in a full-page format.
PASSIVE SATELLITE—A satellite that reflects radio signals back to earth.
PATCH PANEL—A panel used to tie a receiver or transmitter to its associated equipment.
PART—A part is one component or two or more components joined together. It is not normally subject to disassembly without destruction.
PERFORATOR—A device that stores a teletypewriter message on a paper tape. It may be stored for later transmission.
PERIGEE—The point in the orbit of a satellite closest to the earth.
PERMANENT MAGNET SPEAKER—A speaker with a permanent magnet mounted on soft iron pole pieces.
POLAR—The teletypewriter operation where current flow of one polarity represents a mark and current of the opposite polarity represents a space.
POLAR ORBIT—An orbit that has an angle of inclination of or near 90 degrees.
PROGRAMMED TRACKING—The method that uses known satellite orbital parameters to generate antenna pointing angles.
RADIO COMMUNICATIONS—The term describing teletypewriter, voice, telegraphic, and facsimile communications.
RADIO FREQUENCY CARRIER SHIFT—The system that uses a keyer to shift a radio frequency signal above or below an assigned frequency. These shifts correspond to marks and spaces.
RADIO SET CONTROL UNIT—Equipment used to remotely control certain transmitter and receiver functions.
RECEIVER—Equipment that converts electromagnetic energy into a visible or an audible form.
RECEIVER TRANSFER SWITCHBOARD—Equipment used to transfer receiver audio outputs to remote control station audio circuits.
AI-5
RECEPTION—The instant when an electromagnetic wave passes through a receiver antenna and induces a voltage in that antenna.
RED—The reference color of equipment that passes classified information. It normally refers to patch panels.
REPEATER—Another name for an active satellite.
REPERFORATOR—Equipment that converts the incoming tty signal and stores it on paper tape.
REPRODUCTION—The process of converting electrical signals to sound waves. This sound is speech, music, and so on.
REVERSE AGC—The type of agc that causes an amplifier to be driven toward cut-off.
RUNNING OPEN—The teletypewriter condition where the type hammer constantly strikes the type box but does not print or move across the page.
SATELLITE ECLIPSE—An eclipse where the rays of the sun don't reach the satellite. This prevents recharging of the solar cells of the satellite and decreases the power to the transmitter.
SATELLITE-SUN CONJUNCTION—A period when the satellite and sun are close together and the noise from the sun prevents or hampers communications.
SCANNING—The process of subdividing a picture in an orderly manner into segments. This is used in facsimile transmission.
SELECTIVITY—The ability of a receiver to select the desired signal and reject unwanted signals. SENSITIVITY—The ability of a receiver to reproduce very weak signals. The greater the receiver
sensitivity, the weaker the signal that will be reproduced.
SET—A unit or units and the assemblies, subassemblies, and parts connected or associated together to perform a specific function.
SPACING—The condition in teletypewriter operation where a circuit is open and no current flows.
SQUELCH—A circuit that cuts off the output of a receiver when there is no input. START—The first unit of a teletypewriter signal. It is always a space.
STOP—The last unit of a teletypewriter signal. It is always a mark.
SUBASSEMBLY—Consists of two or more parts that form a portion of an assembly or a unit.
SUBHARMONIC—An exact submultiple of the fundamental frequency. Even subharmonics are one- half, one-quarter, and so on. Odd subharmonics are one-third, one-fifth, and so on of the fundamental frequency.
SUPERHIGH FREQUENCY—The band of frequencies from 3 gigahertz to 30 gigahertz. SUPPRESSION—The process of eliminating an undesired portion of a signal.
SYNCHRONOUS—A type of teletypewriter operation where both transmitter and receiver operate continuously.
AI-6
SYNCHRONOUS ORBIT—An orbit in which the satellite moves or rotates at the same speed as the earth.
SYSTEM—A combination of sets, units, assemblies, subassemblies, and parts joined together to form a specific operational function or several functions.
TELECOMMUNICATIONS—The transmission, emission, or reception of signs, signals, writings, images, or sounds. This is done by visual, oral, wire, radio, or other electromagnetic means.
TELETYPEWRITER—A machine that can transmit and or receive letters, numbers, or symbols. It may have a keyboard similar to a typewriter.
TEMPEST—A term normally used to describe compromising emanations. These emanations are unintentionally radiated signals that could disclose classified information.
TIME-DIVISION MULTIPLEXING—The process that periodically samples the full 360 degrees of each sine wave. The sample can be of a received signal or of a signal to be transmitted.
TONE-TERMINAL SET—Equipment that converts tty dc pulses into audio tones for modulation of a transmitter in audio-frequency-tone shift transmissions.
TOP-HAT—An antenna that is center-fed and capacitively loaded.
TRANSITION—The time it takes to shift from a mark to a space condition or from a space to a mark condition.
TRANSMITTER—Equipment that generates and amplifies an rf carrier, modulates the rf carrier with intelligence, and radiates the signal into space.
TRANSMITTER DISTRIBUTOR—A device that reads Baudot code from paper tape and allows a message to be printed on a page printer.
TRANSMITTER TRANSFER SWITCHBOARD—Equipment that selectively transfers remote control station functions and signals to transmitters.
TRIATIC—A special type of monopole antenna array.
ULTRAHIGH FREQUENCY—The band of frequencies from 300 megahertz to 3 gigahertz. UNIT—An assembly or any combination of parts, subassemblies, and assemblies mounted together.
Normally capable of independent operation.
UP LINK—The frequency used to transmit a signal from earth to a satellite.
VERY HIGH FREQUENCY—The band of frequencies from 30 megahertz to 300 megahertz. VERY LOW FREQUENCY—The band of frequencies from 3 kilohertz to 30 kilohertz. WORDS-PER-MINUTE—An approximate rate of speed. It means the number of five letter words with
a space between them that can be transmitted or received in a one-minute period.
ZONE OF MUTUAL VISIBILITY—The area where the satellite can be seen by both the up- and down-link earth terminals.
AII-1
ELF Communications System Program, NAVELEXINST 5430.26, October 1983.
Shipboard Electronics Materials Officer, NAVEDTRA 10478-A, 1982. Electronics Technician, 3 & 2, Vol. 3, NAVEDTRA 10198, 1979.
Cryptologic Technician M 3 & 2, NAVEDTRA 10232-C, 1978.
Radioman 3 & 2, NAVEDTRA 10228-G, 1978.
Howeth, L. S., History of Communications-Electronics in the United States Navy, Bureau of Ships and Of fice of Naval History, Washington, D.C., 1963.
Electronics Technician 3 & 2, Vol. 3, NAVEDTRA 10198, 1979.
Cryptologic Technician M 3 & 2, NAVEDTRA 10232-C, 1978.
Radioman 3 & 2, NAVEDTRA 10228-G, 1978.
Cryptologic Collection Equipments, NAVEDTRA 10251, 1977.
Basic Electronics, Vol. 1, NAVPERS 10087-C, 1970.
Basic Electronics, Vol. 2, NAVPERS 10087-C1, 1979.
Fundamentals of Single Sideband, NAVELEX 0967-LP-222-2010, 1958.
Shipboard Electronics Material Officer, NAVEDTRA 10478-A, 1982. Electronics Technician 3 & 2, Vol. 3, NAVEDTRA 10198, 1979.
Cryptologic Technician M 3 & 2, NAVEDTRA 10232-C, 1978.
The Electronics Material Officer’s Guide to Shipboard Electromagnetic Interference Control, NAVSEASYSCOM STD-407-5287556, 1983.
AII-2
Shipboard Electronics Material Officer, NAVEDTRA 10478-A, 1982. Electronics Technician 3 & 2, Vol. 3, NAVEDTRA 10198, 1979.
Cryptologic Technician M 3 & 2, NAVEDTRA 10232-C, 1978.
Radioman 3 & 2, NAVEDTRA 10228-G, 1978.
Satellite Communications Systems, United States Air Force, KEO-90008, 1972.
Fleet Satellite Communications System Description, Naval Ocean Systems Center, January 1978.
Shipboard Electronics Material Officer, NAVEDTRA 10478-A, 1982. Electronics Technician 3 & 2, Vol. 3, NAVEDTRA 10198, 1979.
Microwave and Tropo-Scatter Communications Systems, NAVELEX 0101,112, 1972.
Vlf, Lf and Mf Communications Systems, NAVELEX 0101,113, 1972. Design Handbook for Optical Fiber Systems, U.S. Army Communications-Electronics,
CCC-CED-XES-78-0l, 1978.
Cooper, Robert S., "SPACE Another Dimension of Defense," Defense 84, August 1984, pp. 12-19.
McGraw-Hill, Vol. 3, Encyclopedia of Science and Technology, 1971. McGraw-Hill, Vol. 12, Encyclopedia of Science and Technology, 1971.
INDEX-1
INDEX-2
INDEX-3
INDEX-4
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
Textbook assignment: Chapter 1, “Introduction to Radio-Frequency Communications,” pages 1-1 through 1-20. Chapter 2, “Introduction to Communications Theory,” pages 2-1 through 2-37.
1-1. For naval communications to be effective, all involved must be top performers. Reliable, secure, and timely receiving and transmitting of information is the goal. Which of the following requirement standards are used to determine whether or not this goal has been met?
1. Wartime 2. Peacetime 3. Cold war less 10 percent 4. Nuclear war less 25 percent
1-2. What are the two types of electrical communications?
1. Radio and wire 2. Television and wire 3. Telegraph and radio 4. Television and radio
1-3. Which of the following terms includes intelligence produced by wire, radio, visual means, oral means or electromagnetic systems?
1. Telecommunications 2. Radiotelegraph 3. Electrolysis 4. Photocopy
1-4. Radiotelegraph (cw) is valuable when communicating to, from, and among widely separated naval units. What is the main advantage of the cw mode?
1. Cost 2. Speed 3. Security 4. Reliability
1-5. Tactical communications is usually
considered as line-of-sight. What maximum distance is normally within the line-of-sight range?
1. 5 miles 2. 25 miles 3. 50 miles 4. 250 miles
1-6. You want to transmit high-speed automatic page or tape copy across an ocean area. Which of the following methods should you choose?
1. Facsimile 2. Radiotelegraph 3. Radiotelephone 4. Radioteletypewriter
1-7. What method is normally used to transmit graphs electronically?
1. Facsimile 2. Radio teletypewriter 3. Frequency-shift keying 4. Audio-frequency-tone shifting
1-8. When you use subdivisions to assign reference designators to equipment, what is the designator of (a) the largest and (b) the smallest?
1. (a) System (b) set 2. (a) Set (b) unit 3. (a) Unit (b) assembly 4. (a) System (b) part
2
1-9. When using the reference designator 1A6A4J6, what level does the number 1 refer to?
1. Subassembly 2. Assembly 3. Group 4. Unit
1-10. What is the total number of frequency bands the military is currently using for communications?
1. 5 2. 7 3. 9 4. 11
1-11. Extremely low-frequency transmissions are primarily directed at which of the following users?
1. Shore installations 2. Surface ships 3. Submarines 4. Aircraft
1-12. Vlf transmitters are used primarily for which of the following purposes?
1. Navigation and fleet communications 2. Frequency standards and time signals 3. Astronomy and oscillator calibration 4. Aircraft control and space vehicle
1-13. Navy use of the low-frequency band is mainly for which, if any, of the following broadcasts?
1. Ship to shore 2. Fleet multichannel 3. Space vehicle telemetry 4. None of the above
1-14. For which of the following reasons does the Navy use only the upper and lower ends of the mf band?
1. They are the most reliable 2. They produce the best propagation 3. The commercial fm band occupies the
middle 4. The commercial AM band occupies
1-15. Hf communications over long-distance trunks, or links between fixed terminals are examples of which of the following types of systems?
1. Fleet broadcast 2. Point-to-point 3. Ground-to-air 4. Ship-to-shore
1-16. Sending a message on several frequencies at once is an example of which of the following transmission types?
1. Time-diversity 2. Phase-diversity 3. Distance-diversity 4. Frequency-diversity
1-17. What type of diversity uses physically separated transmit or receive antennas to improve communications?
1. Time 2. Phase 3. Space 4. Frequency
1-18. Normally the transmission range of vhf is limited to line of sight. What technique is used to increase this range?
1. Tropospheric scatter 2. Atmospheric diversity 3. Ionospheric maneuvering 4. Each of the above
3
1-19. A complex of links make up a major communications system. The naval communications system is further broken down into what two groups?
1. Strategic and local 2. World-wide and local 3. Strategic and tactical 4. Tactical and world-wide
1-20. Communications links have many modes of operation. One terminal in a link has its equipment setup in simplex. The other terminal is using two channels or frequencies in a configuration that allows sending and receiving of different messages at the same time. These two terminals working together make up what mode of operation?
1. Full duplex 2. Half duplex 3. Quasiduplex 4. Semiduplex
1-21. What communications link mode of operation provides telecommunications capability between stations at the same time in both directions?
1. Half duplex 2. Semiduplex 3. Broadcast 4. Duplex
1-22. Aid in restoring downed fleet communications channels is furnished on a not-to-interfere basis by which of the following networks?
1. AUTOSEVOCOM 2. NORATS 3. HICOM 4. DSSCS
1-23. Which of the following switched networks extends tactical voice to shore- based operational commands?
1. NORATS 2. AUTOVON 3. AUTODIN 4. AUTOSEVOCOM
1-24. Of the following transmitter types, which are used for basic communications?
1. Cw, AM, fm, and ssb 2. Fsk, cw, AM, and tty 3. Cw, ssb, voice and fm 4. Voice, tty, fsk, and AM
1-25. Cw transmissions have narrow bandwidths and a high degree of intelligibility under severe noise conditions. What is the primary Navy use for cw?
1. Radioteletypewriter 2. Radiotelegraphy 3. Facsimile 4. Voice
1-26. A cw transmitter must contain which of the following components?
1. A traveling-wave tube 2. A demodulator 3. A combiner 4. A keyer
1-27. In a cw transmitter, a buffer stage performs which of the following functions?
1. Current divider 2. Voltage divider 3. Current amplifier 4. Voltage amplifier
4
1-28. There are differences between low- and high-power transmitters. The main difference is the high power transmitter contains a larger number of which of the following types of amplifiers?
1. Oscillator 2. Final power 3. Intermediate power 4. Intermediate frequency
1-29. In an AM transmitter, audio frequencies are converted into corresponding electrical energy by which of the following components?
1. An oscillator 2. A microphone 3. A modulator 4. A headset
1-30. In an fm transmitter, a varicap performs which of the following functions?
1. It amplifies the outgoing signal 2. It varies the oscillator frequency 3. It demodulates the outgoing signal 4. It multiplies the oscillator frequency
1-31. If an oscillator has a fundamental frequency of 3,550 megahertz, what is the frequency of the third harmonic?
1. 5,325 megahertz 2. 7,100 megahertz 3. 9,875 megahertz 4. 10,650 megahertz
1-32. If the fundamental frequency of an rf carrier is 1,000 kilohertz, what is the frequency of the fourth subharmonic?
1. 500 kilohertz 2. 333 kilohertz 3. 250 kilohertz 4. 200 kilohertz
1-33. Oscillator output frequencies are raised to usable values by frequency multipliers. To raise an oscillator frequency from 20 megahertz to 120 megahertz, what combination of frequency multipliers would be used?
1. Two doublers 2. A doubler and a tripler 3. A doubler and a quadruplet 4. A tripler and a quadruplet
1-34. When an AM signal leaves the antenna of a transmitter, which of the following frequency components does the signal contain?
1. The carrier 2. The upper sideband 3. The lower sideband 4. All of the above
1-35. In a single-sideband transmitter, selection of the desired sideband and suppression of the other is done by which of the following components?
1. Mixer 2. Filter 3. Detector 4. Oscillator
1-36. When compared to a conventional AM signal, an ssb signal provides which of the following advantages?
1. Improved frequency stability 2. Increased receiver gain 3. Reduced distortion 4. Reduced bandwidth
1-37. For ship-to-shore teletypewriter circuits, which of the following types of multiplexing is/are used?
1. Time and/or phase 2. Time and/or frequency 3. Phase and/or modulation 4. Frequency and/or modulation
5
1-38. Operators of transmitters and receivers use a circuit to coordinate the service of messages and to make frequency changes. What is the name of this circuit?
1. Order-wire circuit 2. Documentation circuit 3. Synchronization circuit 4. Operator-eyes-only circuit
1-39. A transmitted electromagnetic wave enters an antenna, induces a voltage into it, and passes that voltage to a receiver. What is this chain of events called?
1. Reproduction 2. Selection 3. Detection 4. Reception
1-40. When a receiver picks one frequency out from all other frequencies, it's performing which of the following basic functions?
1. Selection 2. Reception 3. Detection 4. Reproduction
1-41. When a receiver separates the audio frequencies from the radio-frequency carrier it is performing which of the following basic functions?
1. Reception 2. Selection 3. Detection 4. Reproduction
1-42. The receiver action of converting electrical energy to a usable format, such as sound, is an example of which of the following basic functions?
1. Reception 2. Selection 3. Detection 4. Reproduction
1-43. Which of the following measurements provides an indication of the ability of a receiver to reproduce weak signals?
1. Bandwidth 2. Sensitivity 3. Selectivity 4. Frequency response
1-44. Overall sensitivity of a receiver is limited by which of the following factors?
1. Noise 2. Bandwidth 3. Output power 4. Frequency response
1-45. How is a receiver's ability to reject unwanted signals and receive desired signals determined?
1. Noise 2. Fidelity 3. Selectivity 4. Sensitivity
1-46. When high fidelity is your prime consideration you should select a receiver that has been designed with which of the following features?
1. High gain 2. High output power 3. Broadband frequency selection
circuits 4. Narrowband frequency selection
1-47. The IF frequency in a receiver is produced by which of the following methods?
1. Modulation 2. Heterodyning 3. Frequency synthesis 4. Frequency multiplication
6
1-48. The process of heterodyning takes place in which of the following receiver circuits?
1. Mixer 2. Comparator 3. Oscillator 4. Second IF amplifier
1-49. Of the following frequencies, which one is a typical value of IF for AM communications receivers?
1. 455 kilohertz 2. 554 kilohertz 3. 455 megahertz 4. 554 megahertz
1-50. Two or more circuits within a receiver are varied by a single control through the use of which of the following processes?
1. Ganged tuning 2. Frequency synthesis 3. Automatic gain control 4. Automatic frequency control
1-51. There are electrical differences between AM and fm receivers. An fm receiver contains which of the following circuits?
1. Comparator 2. Discriminator 3. Limiter 4. Both 2 and 3 above
1-52. An fm signal has which of the following characteristics when compared to an AM signal?
1. More noise 2. Less static 3. A higher power output 4. A lower operating frequency
1-53. Ssb transmissions have which of the following characteristics when compared to AM transmissions?
1. Wide bandpass frequencies 2. Concentrated power 3. Less modulation 4. High fidelity
1-54. Single sideband receivers use a special oscillator. The output of that oscillator is fed directly to the detector circuit. What type of oscillator is used?
1. Local 2. High frequency 3. Variable frequency 4. Carrier reinsertion
1-55. A transmitter has a suppressed carrier frequency of 4 megahertz and is radiating only an upper sideband signal. When the intelligence is a 1-kilohertz tone, which of the following sideband frequencies will be transmitted?
1. 3,999 kilohertz 2. 4,000 kilohertz 3. 4,001 kilohertz 4. Both 2 and 3 above
1-56. Manual gain lets you adjust a receiver for maximum sensitivity and amplify weak input signals. Which of the following internal sections of the receiver are varied by this control?
1. Oscillator 2. Audio frequency 3. Radio frequency 4. Intermediate frequency
1-57. Manual volume control of a receiver internally varies the input to which of the following circuits?
1. Detector 2. Audio amplifier 3. Frequency converter 4. Radio frequency amplifier
7
1-58. Changes in receiver input strength due to changing atmospheric conditions is described by which of the following terms?
1. Gain 2. Fading 3. Ducting 4. Trapping
1-59. The rf amplifier connected to your receiving antenna has a voltage gain of 240. When the antenna is receiving a signal of 8 microvolts, what will be the maximum output voltage of the rf amplifier?
1. 1.92 millivolts 2. 2.91 microvolts 3. 30 microvolts 4. 33 millivolts
Figure 1A.
IN ANSWERING QUESTIONS 1-60 AND 1-61, REFER TO FIGURE 1A. 1-60. If the agc diode shorts, which of the
following actions would result?
1. There would be no aqc 2. There would be no delay 3. The agc diode would be reverse
biased 4. The polarity of the agc would be
1-61. The amount of agc feedback depends on attaining an established received signal strength. If the established signal strength is set for 50 microvolts, and the input signal measures 44 microvolts, approximately which, if any, of the following values of agc is developed?
1. 44 microvolts 2. 50 microvolts 3. 94 microvolts 4. None of the above
1-62. To automatically compensate for input
signal strength variations within a receiver, which of the following types of circuits are added?
1. Afc 2. Nfc 3. Agc 4. Nsu
1-63. AgC circuitry within a receiver uses a portion of which of the following detector voltage components as a feedback signal to preceding stages?
1. Dc 2. Ac 3. IF 4. Audio
1-64. Which of the following types of agc voltage drives an amplifier toward cutoff?
1. Saturation 2. Delayed 3. Reverse 4. Forward
8
1-65. What is the purpose of the squelch circuit in a receiver?
1. To attenuate very strong signals in
2. To suppress receiver noise output when no input signal is being received
3. To suppress the electronic "whine" of the rf amplification stage
4. To reject signals of other than the desired frequency should the receiver drift off frequency
1-66. How does a receiver accomplish the
squelch function?
1. By proportional blocking of the rf amplifier stage output
2. By blocking the detector or audio amplifier when there is no signal
3. By switching an inductive/capacitive filter into the output of the last rf amplifier
4. By switching in a matched-frequency stage which passes matching frequencies and rejects all others
1-67. A quartz crystal filter is used in a
communications receiver to improve which of the following characteristics?
1. Fidelity 2. Sensitivity 3. Selectivity 4. Reproduction
Figure 1B.
IN ANSWERING QUESTION 1-68, REFER TO FIGURE 1B. 1-68. When the wiper of R1 is placed in the
full treble position, which of the following actions occur?
1. Bass response is improved 2. High frequency shunting is reduced 3. Higher frequencies are shunted to
ground 4. The capacitor and resistor are placed
1-69. Automatic frequency control circuits are used in a receiver for which of the following purposes?
1. To adjust IF amplifier gain 2. To correct for oscillator frequency
drift 3. To extend the frequency range of the
receiver 4. To automatically tune the receiver to
9
Figure 1C.
IN ANSWERING QUESTIONS 1-70 AND 1-71, REFER TO FIGURE 1C. 1-70. What is the phase relationship between
the input signals fed to the diodes?
1. In phase 2. 90 degrees out of phase 3. 180 degrees out of phase 4. 270 degrees out of phase
1-71. A change in oscillator frequency will change which of the following input relationships between the sawtooth reference voltage and the incoming signal?
1. Phase 2. Voltage 3. Current 4. Amplitude
1-72. How is the long term stability and accuracy required of modern communications receivers attained?
1. Through the use of a single, crystal-
2. Through the use of an electron- coupled oscillator, as the local oscillator
3. Through a process of automatic frequency control
4. Through a process known as frequency synthesis
1-73. When using the frequency synthesis process, a signal of the desired accuracy and stability is produced by which, if any, of the following methods?
1. Automatic frequency control, that is,
2. Using a crystal-controlled oscillator to produce a stable high frequency, and through the process of frequency division selecting a subharmonic of this frequency as the desired frequency
3. The heterodyning and selection of frequencies which are not harmonically related to each other
4. None of the above
1-74. Permanent magnet speakers respond quite well to which of the following audio frequency ranges?
1. Low 2. High 3. Mid band 4. Each of the above
1-75. For which of the following reasons do most standard Navy headphones respond poorly to low frequencies?
1. Small diaphragm size 2. Diaphragm inflexibility 3. Both 1 and 2 above 4. Input signal filtering
10
Textbook assignment: Chapter 3, “Fundamental Systems Equipment,” pages 3-1 through 3-47. ___________________________________________________________________________________
2-1. In a basic communications voice system, which of the following functions occur in the handset during the receive process?
1. Correction voltages are fed to the local oscillator
2. Phasing voltages are received from the master oscillator
3. Voice energy is transformed into electronic impulses
4. Electrical energy is converted to acoustical energy
2-2. Radio set control units are often used aboard ship to remotely control transmitters and receivers. Under standard operating conditions what is the maximum number of units that can be paralleled with a single transmitter and receiver group?
1. One 2. Two 3. Eight 4. Four
2-3. When you are using a transmitter transfer switchboard, what is the maximum number of transmitters that may be connected to a single remote control station?
1. One 2. Two 3. Eight 4. Four
THIS SPACE LEFT BLANK INTENTIONALLY.
2-4. You are using a radio set control unit to remotely control 1 of 8 transmitters. Operating knob number 1 on transmitter transfer switchboard number 1 is used to select transmitters 1 through 6. If you want to control transmitter number 7, what switch position must be selected?
1. 1 2. Any of 1-6 3. X 4. OFF
2-5. On a receiver transfer switchboard, each switch position is connected to what maximum number of receivers?
1. One 2. Two 3. Three 4. Four
IN ANSWERING QUESTIONS 2-6 THROUGH 2-13, REFER TO THE RADIO TRANSMITTING SET DISCUSSED IN CHAPTER 3.
2-6. The impedance matching of equipment to transmission line is accomplished by which of the following equipment groups?
1. A radio transmitter 2. An antenna coupler 3. An rf amplifier 4. A power supply
2-7. The output power of the transmitter unit drives which of the following units?
1. The rf amplifier 2. The power supply 3. The antenna coupler 4. The antenna coupler control
11
2-8. The rf amplifier receives digital tuning information that is generated in which of the following units?
1. The receiver 2. The transmitter 3. The coupler control 4. The radio set control
2-9. In some installations tuning must be done without the use of rf power, as rf is suppressed except during brief transmission periods. Under these conditions, which of the following methods of tuning should be used?
1. Silent 2. Anti-jam 3. Automatic 4. Semiautomatic
2-10. Operator controlled tuning of the antenna coupler group by the use of front panel controls is possible during which of the following modes of operation?
1. Silent and manual 2. Manual and automatic 3. Semiautomatic and silent 4. Automatic and semiautomatic
2-11. Once tuned, the antenna coupler is able to handle which of the following maximum amounts of power?
1. 500 watts average 2. 2,000 watts average 3. 250 watts peak envelope 4. 1,000 watts peak envelope
2-12. The antenna coupler is pressurized with dry nitrogen for which of the following reasons?
1. To prevent corona 2. To prevent arcing 3. To aid in internal heat transfer 4. Each of the above
2-13. You are using the cw mode of the radio transmitter unit. The 500-kilohertz local carrier is directly inserted into which of the following circuits?
1. The rf amplifiers 2. The IF amplifiers 3. The modulator 4. The detector
IN ANSWERING QUESTIONS 2-14 THROUGH 2-16, REFER TO THE RADIO RECEIVER DISCUSSED IN CHAPTER 3.
2-14. Adjacent-channel selectivity and image- frequency suppression have been improved in this receiver by the addition of which of the following features?
1. Digital tuning 2. Triple conversion 3. Front panel readout 4. Very accurate frequency standard
2-15. The full accuracy of the frequency standard is sacrificed when which of the following types of tuning is used?
1. Vernier 2. Automatic 3. 1-kilohertz incremental 4. 100- or 500-hertz incremental
2-16. The receiver demodulates and provides audio outputs for which of the following types of received signals?
1. Fm, AM, and fsk 2. AM, cw, and isb 3. Cw, fm, and isb 4. Lsb, usb, and fm
2-17. A receiving antenna patch panel serves which of the following functions?
1. Terminates lines leading to receivers 2. Terminates incoming antenna
transmission lines 3. Both 1 and 2 above 4. Physically connects transmitters to
12
2-18. Transmitting antenna patch panels are interlocked with the transmitter for which of the following reasons?
1. Safety 2. Ease of operation 3. Ease of maintenance 4. Both 2 and 3 above
2-19. A transmit multicoupler provides which of the following functions?
1. Receiver isolation 2. Transmitter tuning 3. Additional amplification 4. Isolation between transmitters
2-20. In a manual telegraph circuit, the only two conditions are marking and spacing. Marking is characterized by which of the following descriptions?
1. The key is open 2. Current is flowing 3. Current is not flowing 4. The armature is retracted by a spring
2-21. A teletypewriter code signal consists of 7 units. Of the following functions, which describes the middle 5 units?
1. Provides channel data 2. Carries the intelligence 3. Signals stop information 4. Signals start information
2-22. Which of the following terms describe the time between a space and mark or mark and space condition in a teletypewriter?
1. Movement 2. Variation 3. Transition 4. Character interval
2-23. The time interval between words when using the Morse code is equal to which of the following durations?
1. 1 dot 2. 7 dots 3. 3 dashes 4. 5 dashes
2-24. When you are using the five-unit code in teletypewriter operation, what is the maximum number of combinations available that will print letters, figures, function signs, and numerals?
1. 30 2. 32 3. 60 4. 74
2-25. When you are using the teletypewriter five-unit code, which of the following signals are used to increase the printing capacity of the equipment?
1. Inverter 2. Combiner 3. Case-shift 4. Type-adjust
2-26. Which, if any, of the following modes of teletypewriter operation is more often used in high-speed data systems?
1. Start-stop 2. Synchronous 3. Asynchronous 4. None of the above
2-27. In teletypewriter operation, what term defines the length of time required to transmit one letter, figure, function sign or numeral?
1. Baud rate 2. Bit speed 3. Code length 4. Character interval
13
2-28. Synchronous teletypewriter systems are characterized by which of the following features when compared to asynchronous systems?
1. Internal timing signals are always used
2. Only the start-stop element must be transmitted
3. Only the intelligence elements must be transmitted
4. Signal quality determines receiver line signal condition
2-29. When you are referring to the unit of teletypewriter signaling speed, the reciprocal of the time (in seconds) of the shortest signal element is described by which of the following terms?
1. Unit code 2. Baud rate 3. Bits per second 4. Words per minute
2-30. The teletypewriter condition where current flow represents a mark and no current flow represents a space occurs in which of the following types of operation?
1. Polar 2. Arctic 3. Biased 4. Neutral
2-31. You are using neutral keying and the teletypewriter type hammer continually strikes the type box but there is no printing or type box movement across the page. What is the name of this condition?
1. Debugging 2. Running open 3. Baudot blanking 4. Decoding at random
2-32. Of the following equipment which one changes teletypewriter dc pulses to mark and space modulation for the transmitter carrier wave?
1. A comparator 2. A modulator 3. A converter 4. A keyer
2-33. To change an rf signal to do pulses for teletypewriter operation, you must use a receiver and what other piece of equipment?
1. A keyer 2. A converter 3. A comparator 4. A demodulator
2-34. A tone-modulated radio teletypewriter system uses what modulation method to change dc mark and space impulses into audio electrical impulses?
1. Amplitude 2. Frequency 3. Phase 4. Pulse
2-35. In a basic tone-modulated radio teletypewriter system, separation of the audio signal from the carrier is accomplished by what process?
1. Conversion 2. Modulation 3. Selection 4. Detection
2-36. In a radio-frequency-carrier shift system, what equipment is the source of radio- frequency excitation voltages?
1. The inverter 2. The converter 3. The comparator 4. The transmitter keyer
14
2-37. The keyer in a radio-frequency-carrier shift system is normally adjusted for which of the following maximum frequency spreads?
1. 425 hertz 2. 500 hertz 3. 750 hertz 4. 850 hertz
2-38. Of the following teletypewriter equipment, which one is used to store incoming teletypewriter messages on tapes for future transmission on a transmitter distributor?
1. A keyboard 2. A page printer 3. A typing reperforator 4. A communication patching panel
2-39. Teletypewriter patch panels perform which of the following functions?
1. They provide a means for connecting the teletypewriter equipment in various combinations
2. They provide a means for permanently connecting commonly used combinations of equipment
3. They provide a central point for connecting the dc supply voltage to the teletypewriter circuits
4. Each of the above
2-40. You are working with a teletypewriter patch panel. What color signifies that secure information is being passed?
1. Red 2. Gray 3. Black 4. Green
2-41. In any switching operation between plugs and jacks of a teletypewriter panel, if the cord plug is pulled from the set (machine) jack before the plug is removed from the looping jack, which of the following conditions will occur?
1. A dangerous dc voltage will be produced on the exposed plug
2. All teletypewriter messages in the channel will be interrupted
3. Both 1 and 2 above 4. Classified information will be
2-42. Cryptographic equipment performs which, if any, of the following functions?
1. Encodes and decodes messages 2. Reduces mean-time between
messages 3. Acts as an additional power amplifier 4. None of the above
2-43. In the radio-frequency-carrier shift system, translation of an rf signal to an audio signal is done by which of the following equipment?
1. A converter 2. A comparator 3. A radio receiver 4. An antenna filter
2-44. A comparator compares signal strength during which of the following types of receiver operation?
1. Single 2. Space diversity 3. Frequency diversity 4. Both 2 and 3 above
15
2-45. In an afts transmit system, the conversion of dc signals into audio tone-shift signals is done by which of the following pieces of equipment?
1. Cryptographic 2. Tone terminal set 3. Converter/comparator 4. Modulator/demodulator
2-46. The process of simultaneous transmission of several intelligible signals on the same frequency during the same period of time is called
1. duplexing 2. simplexing 3. complexing 4. multiplexing
2-47. What are the two methods of multiplexing?
1. Time-division and frequency- multiplication
2. Time-division and frequency-division 3. Time-multiplication and frequency-
multiplication 4. Time-multiplication and frequency-
2-48. In time-division multiplexing, assume that a 4,000-hertz tone is applied to each of six channels in a telegraph transmitter and that each channel is to be sampled at a rate of 2. 5 times during each cycle of the 4,000-hertz tone. At what speed, in revolutions per second, must the rotating switch turn to accomplish this sampling rate?
1. 3,000 2. 4,000 3. 7,200 4. 10,000
2-49. In time-division multiplexing, what drawback is encountered if an excessive number of frequency channels is used?
1. Static is increased 2. Bandwidth is increased 3. Switching becomes unreliable 4. Reception becomes unintelligible
2-50. How many times per cycle is a practical time-division multiplex system optimumly sampled?
1. 1.5 2. 2.0 3. 2.4 4. 3.1
2-51. Frequency-division multiplexing systems transmit and receive during a maximum of how many degrees of a sinewave?
1. 90 2. 180 3. 270 4. 360
2-52. By using frequency-division multiplexing, tty circuits may carry a maximum of how many single, 3,000- hertz channels?
1. 12 2. 16 3. 18 4. 24
2-53. In a 16-channel tty-multiplexing system, the maximum difference between a mark and a space, for any give channel, is how many hertz?
1. 85 2. 382.5 3. 425 4. 467.5
16
2-54. Weather charts and photographs are examples of materials transmitted by
1. aw telegraphy 2. FAX (facsimile) 3. landline teletypewriter 4. rttv (radio teletypewriter)
2-55. Which of the following facsimile transceiver operations consists of subdividing the picture in an orderly manner and into a large number of segments?
1. Scanning 2. Recording 3. Receiving 4. Transmitting
2-56. The scanning operation is accomplished in the facsimile transmitter by a
1. scanning drum and a phototube arrangement
2. scanning drum and aperture tube 3. spiral drum and amplifier 4. phototube amplifier
2-57. The purpose of the phototube in facsimile equipment is to
1. illuminate a segment of the picture 2. produce the carrier signal for the
exciter lamp 3. maintain the output voltage at a
predetermined fixed value 4. transform varying amounts of light
2-58. Which of the following means is used to synchronize the receiving drum with the transmitting drum in a radio facsimile system?
1. The drums are mechanically linked 2. Each drum is started by an accurate
clock 3. Both drums are operated by
synchronous motors 4. Both drums are stepped around a
2-59. In a facsimile system, which of the following methods is used to accomplish framing at the receiver unit?
1. A synchronous clutch mechanism is actuated
2. A primary time/frequency standard is switched in
3. A series of phasing pulses are transmitted prior to image transmission
4. A synchronous motor at both the transmitter and receiver is engaged
2-60. Of the following terms, which one is primarily concerned with compromising emanations?
1. Tempest 2. Radiation hazard 3. Quality monitoring 4. Electromagnetic interference
2-61. Of the following fundamental requirements of a military communications system, which one, if any, is most important?
1. Speed 2. Security 3. Reliability 4. None of the above
2-62. What one assumption may be made regarding all military radio transmissions?
1. They are secure 2. They have been encrypted 3. They have been decrypted 4. They have been intercepted
2-63. Scheduled maintenance in support of QMCS is designed to alert you to which of the following problems?
1. Safety hazards 2. Equipment failure 3. System degradation 4. Improper operating procedures
17
2-64. Of the following terms, which one is defined as the ability of an electronic system to perform its individual functions without interference?
1. Electronic countermeasures 2. Electromagnetic interference 3. Electromagnetic compatibility 4. Electronic counter-countermeasures
2-65. The sources of electromagnetic radiations that reduce receiver performance are known by which of the following terms?
1. Electronic countermeasures 2. Electromagnetic interference 3. Electromagnetic compatibility 4. Electronic counter-countermeasures
2-66. Which of the following categories of electromagnetic interference includes interference generated by electrically charged raindrops?
1. Natural 2. Functional 3. Incidental 4. Hull-generated
2-67. Cross modulation is a form of emi where the desired carrier intermodulates with an undesired signal. Which of the following devices should minimize this interference?
1. Filters 2. Preselectors 3. Both 1 and 2 above 4. Preamplifiers
2-68. Shipboard receive systems are designed to include protective circuitry between the antenna and the receiver that prevent which of the following problems?
1. Degradation of overall receiver performance by processing of off- frequency signals
2. Decrease of desired signal amplification
3. Burn out of front-end stages 4. Each of the above
2-69. Of the following body organs, which are considered the most vulnerable to radiation hazards (RADHAZ)?
1. Eyes and testes 2. Heart and lungs 3. Liver and spleen 4. Kidneys and brain
2-70. Which of the following methods of reducing rf burn hazards is the most useful and widespread technique used?
1. Operate receivers only 2. Vary the operating frequency 3. Bond and ground all metallic objects 4. Operate transmitters only at low
2-71. The greatest hazard from thermal effects appears to come from equipment operated in which of the following frequency ranges?
1. 1 to 3 gigahertz 2. 2 to 30 megahertz 3. 30 to 300 kilohertz 4. 225 to 500 megahertz
18
2-72. You have been working on a piece of equipment and your eyes have been exposed to high-intensity microwaves. Which of the following types of eye problems may occur?
1. Detached retina 2. Conjunctivitis 3. Cataracts 4. Glaucoma
19
Textbook assignment: Chapter 4, “Introduction to Satellite Communications,” pages 4-1 through 4-21. Chapter 5, “Introduction to Miscellaneous Systems and Equipment,” pages 5-1 through 5-20.
3-1. What artificial satellite is credited with starting the era of space technology?
1. Vela 2. Midas 3. Score 4. Sputnik
3-2. There are two types of communications satellites. What type acts as a repeater for the signal?
1. Active 2. Passive 3. Reflecting 4. Retransmitting
3-3. Transmission of information to a satellite is done on what frequency?
1. Up-link 2. Down-link 3. Transponder 4. Termination
3-4. An earth terminal receives signals on what frequency?
1. Up-link 2. Transmit 3. Down-link 4. Termination
3-5. Of the following orbit parameters, which one describes the basic orbit shape of a communications satellite?
1. Inclined or polar 2. Polar or equatorial 3. Elliptical or circular 4. Synchronous or nonsynchronous
3-6. When the period of an orbit is identical to that of the earth, the orbit is
1. synchronous 2. asynchronous 3. subsynchronous 4. near-synchronous
3-7. What is the parameter in the orbit of a satellite that refers to the point nearest the center of the earth?
1. Apogee 2. Perigee 3. Altitude 4. Inclination
3-8. As a reference, perigee and apogee are measured in which of the following units?
1. Nautical miles 2. Statute miles 3. Light years 4. Kilometers
3-9. A satellite which has a flight path that does not coincide with the equatorial plane of the earth is said to be in what type if orbit?
1. A circular 2. An inclined 3. An elliptical 4. An equatorial
20
3-10. A satellite orbiting with an angle of inclination of approximately 90 degrees describes which of the following types of orbit?
1. Polar 2. Equatorial 3. Synchronous 4. Asynchronous
3-11. In order to cover most of the earth except the polar regions, what is the minimum number of satellites that mast be orbited?
1. 5 2. 6 3. 3 4. 4
3-12. There were many limitations that caused problems on the first communications satellites. Of the following problems, which one was considered the most severe?
1. The excessive size 2. The excessive weight 3. The too low orbit altitude 4. The lack of a suitable power source
3-13. Which of the following power sources is/are considered a practical choice for satellites?
1. Solar cells only 2. Storage batteries only 3. A combination of solar cells and
storage batteries 4. Sunlight and leclanche cells
3-14. What development in satellite communications improved back-up power during eclipses?
1. The installation of a battery back-up 2. The installation of a nuclear power
source 3. The continuous exposure of solar
cells to the sun 4. The increase in solar cells mounted
3-15. Why is satellite orientation in space so important?
1. Because it is a necessity for back-up power
2. To meet the requirements of spin stabilization
3. To ensure that sunlight converging on the solar cells is converted to electrical power
4. Because it is essential for maximum solar cell exposure to the sun and satellite antenna visibility to earth terminals
3-16. Why are communications satellite earth terminals generally located in areas remote from the actual users?
1. To minimize cost 2. To minimize jamming 3. To minimize rf interference 4. To allow for future expansion
3-17. Which of the following characteristics is a requirement for a satellite earth terminal antenna?
1. It must be omnidirectional 2. It must be of the Franklin collinear
type 3. It must have low gain and be highly
directional 4. It must be capable of transmitting and
3-18. One earth terminal antenna uses a cluster of four 10-foot parabolic antennas. This array is effectively a total of how many feet in diameter?
1. 18 2. 20 3. 32 4. 40
21
3-19. Why do satellite earth terminals require highly sensitive receivers?
1. To overcome the down-link power losses
2. To permit extraction of the desired communications information from the received signal
3. Both 1 and 2 above 4. Because of the signal scatter effect of
3-20. Which of the following functions is performed by the exciter stage of an earth terminal transmitter?
1. Modulation of the IF carrier 2. Translation of the IF signal to the up-
link frequency 3. Amplification of the IF signal to the
level required by the receiver 4. Conversion of the down-link
3-21. Telemetery equipment used in satellite communications systems performs which of the following functions?
1. They monitor the operating conditions within the satellite
2. They provide local control for satellite operations
3. They furnish high-capacity wide-band tty trunks
4. They measure ambient weather conditions
3-22. A typical shipboard receive-only satellite system uses which of the following types of modulation?
1. Pulsed or amplitude 2. Pulsed or frequency 3. Amplitude or phase-shift-key 4. Frequency or phase-shift-key
3-23. Locating a near-synchronous satellite is rather simple for which of the following reasons?
1. It is stationary 2. It is moving north to south 3. It has a slow relative motion 4. It has a fast relative motion
3-24. What is the name of the table that provides coordinates of a satellite at specific times?
1. Bearing location 2. Longitudinal 3. Propagation 4. Ephemeris
3-25. To establish radio contact with a satellite, an earth terminal must know which of the following satellite data?
1. Attitude 2. Elevation 3. Operating speed 4. Angle of inclination
3-26. Satellite down-link frequency variations occur most often from satellites in which of the following orbits?
1. Low altitude elliptical 2. Medium altitude circular 3. High altitude synchronous 4. Superhigh altitude near-synchronous
3-27. Of the following terms, which one describes the period of time required for one earth terminal to yield control of a satellite to another?
1. Slewing 2. Hand over 3. Control shift 4. Terminal continuity
22
3-28. When compared to hf communications, which of the following advantages are unique to satellite communications links?
1. They are more reliable and flexible 2. They are unaffected by propagation
variations affecting hf 3. They do not require repeater stations
or troposcatter links 4. Each of the above
3-29. Which of the following factors limits the reliability of active satellite communications system?
1. The reflection or refraction of signals 2. The reliability of the equipment used 3. The skill of the operating and
maintenance personnel 4. Both 2 and 3 above
3-30. An increase of invulnerability to jamming of satellite communications systems is seen through the use of which of the following features?
1. Narrow bandwidths 2. Low transmitter output power 3. Antijamming modulation techniques 4. Omnidirectional earth terminal
3-31. Which of the following statements best describes the advantage of satellite communications in terms of flexibility?
1. The antenna group of any earth terminal can be mounted on the weather deck of a ship
2. Certain earth terminals are housed in vans and can be transported to remote areas
3. Military satellite communications are capable of handling hundreds of voice channels
4. A high degree of protection from jamming is afforded by the highly Directional antennas at earth terminals
3-32. A satellite communications system is limited by which of the following characteristics?
1. The attitude of the satellite repeater 2. The technical design of the satellite 3. The immobility of the satellite 4. The mobility of the satellite
3-33. Active communications satellite systems have two major limitations. What are they?
1. Complex preamplifiers and high gain antennas
2. Up-link transmitter power and earth terminal antenna size
3. Down-link transmitter power and uplink receiver sensitivity
4. Down-link receiver sensitivity and external atmospheric noise
3-34. The rf power output of a satellite communications system is severely limited due to which of the following factors?
1. A lack of adequate jamming capabilities
2. An inefficient solar-cell package aboard the satellite
3. An unstable satellite orientation with respect to the horizon
4. A requirement for large antenna-farm earth-terminal systems
3-35. The availability of a satellite to act as a relay station between two earth terminals depends upon which of the following considerations?
1. The mobility of the satellite 2. The location of the earth terminals 3. The operating frequencies of the
satellite 4. The electronic design of the earth
23
3-36. What determines the length of time that a nonsynchronous satellite in a circular orbit will be in the zone of mutual visibility?
1. Height of the orbit 2. Earth terminal antenna size 3. Down-link transmitter power 4. Up-link receiver sensitivity
3-37. Satellite communications systems are being rapidly developed by the Navy for which of the following reasons?
1. To replace microwave links 2. To relieve dependence on hf
communications 3. To reduce procurement and
development costs 4. To replace all physically large size
3-38. In an mf transmitter, the frequency generator is used during which of the following modes of operation?
1. AM 2. Fm 3. Cw 4. Fsk
3-39. The pre-ipa and ipa in an mf transmitter are which of the following types?
1. Linear, tuned 2. Linear, untuned 3. Non-linear, tuned 4. Non-linear, untuned
3-40. Of the following communications system components, which one is a device that is nonradiating, absorbs rf, and has the characteristic impedance of the antenna?
1. Helix 2. Dummy load 3. Rf tuning unit 4. Frequency synthesizer
3-41. Which of the following antenna arrays consists of quarter-wave, vertically polarized stubs?
1. Broadside 2. Parasitic 3. Top-hat 4. Triatic
IN ANSWERING QUESTIONS 3-42 THROUGH 3-44, REFER TO THE MEDIUM FREQUENCY AND BELOW RECEIVER COVERED IN CHAPTER 5.
3-42. With one exception, the receiver has the same circuitry as any high frequency receiver. What is the one exception?
1. The components are doubled up 2. The local oscillator is eliminated 3. The radio-frequency amplifier is
replaced by a video amplifier 4. The audio-frequency amplifier is
3-43. The rejection of input frequencies above 900-kilohertz is performed by which of the following circuits?
1. An attenuator 2. A video amplifier 3. A low-pass filter 4. A calibration oscillator
3-44. The demodulation of ssb, cw, and fsk signals is performed by which of the following circuits?
1. An fm detector 2. A phase splitter 3. An audio amplifier 4. A product detector
24
3-45. Of the following amplifiers, which one has a high gain, low noise, wide bandwidth and is operated in the microwave region?
1. A magnetic 2. An operational 3. A differential 4. A traveling-wave-tube
3-46. In a line-of-sight communications system, propagation is affected by which of the following layers of the atmosphere?
1. Ionosphere 2. Troposphere 3. Stratosphere 4. Thermosphere
3-47. Horn-driven paraboloid antennas have which of the following characteristics?
1. High gain, narrow beam width 2. Low gain, narrow beam width 3. High gain, wide beam width 4. Low gain, wide beam width
3-48. Line-of-sight systems are configured in many ways with regards to channel width and number of channels. A voice system with a channel width of 4-kilohertz has a total of how many channels available for transmission?
1. 200 2. 400 3. 600 4. 800
3-49. A one-hop transmission of a tropo-scatter system can travel what maximum distance?
1. 1200 miles 2. 1000 miles 3. 800 miles 4. 500 miles
3-50. Of the following advantages, which one is primary to the NTDS when compared with conventional data systems?
1. Speed 2. Distance 3. Security 4. Reliability
3-51. The NTDS uses which of the following data transmission links?
1. 14, 11, 4A 2. 14A, 11, 4 3. 14, 11A, 4 4. 14A, 11A, 4A
3-52. Of the following NTDS links, which one(s) is/are only used as a one-way broadcast?
1. 14 2. 4A 3. 11, 14 4. 4A, 11
3-53. Portable radio sets are used primarily for which of the following types of communications?
1. Amphibious 2. Air-to-air 3. Electronic warfare 4. Anti-submarine warfare
3-54. When designing portable and pack radios, which of the following characteristics is the prime consideration?
1. Must be solar powered 2. Must be heavy and rugged 3. Must have high output power 4. Must be light-weight and compact
25
IN ANSWERING QUESTIONS 3-55 THROUGH 3-58, REFER TO THE EMERGENCY LIFEBOAT TRANSMITTER COVERED IN CHAPTER 5.
3-55. Search and rescue stations are divided into groups that have distinct rescue functions. Emergency lifeboat transmissions are designed for reception by a total of how many of these groups?
1. 5 2. 2 3. 3 4. 4
3-56. What are the operating frequencies of the transmitter?
1. 8,364 kHz and 500 MHz 2. 500 MHz and 8,864 kHz 3. 500 kHz and 8,364 kHz 4. 500 kHz and 8,864 kHz
3-57. What is the primary source of power for the transmitter?
1. External ac 2. Wind generator 3. Internal battery 4. Handcrank generator
3-58. When in the automatic mode of operation, the transmitter transmits (a) while changing frequency every (b) seconds?
1. (a) The SOS distress signal (b) 50
2. (a) Voice messages (b) 20
3. (a) Voice messages (b) 50
4. (a) The SOS distress signal (b) 20
3-59. What is the maximum number of channels available when you are using the emergency portable transceiver covered in chapter 5?
1. 5 2. 2 3. 3 4. 4
3-60. A laser operates in which of the following areas of the light spectrum?
1. Red 2. Infrared 3. Ultraviolet 4. At or near visible light
3-61. The principle of the laser is much like that of, which of the following electronic components?
1. Hall generator 2. Reflex klystron 3. Traveling-wave-tube 4. Very high-Q cavity resonator
3-62. Which of the following components is a close relative of the laser?
1. Thyristor 2. Photo transistor 3. Light emitting diode 4. Photovoltaic transducer
3-63. Laser transmissions during adverse weather conditions experience which of the following problems?
1. Absorption 2. Refraction 3. Reflection 4. Diffraction


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Big-T is in his senior year at the Academy of Art University. He hopes to graduate in May
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