FCC3 Flashcards
Study for FCC exam
What are the distinguishing features of a Chebyshev filter?
It allows ripple in the passband.
What are the distinguishing features of a Butterworth filter?
It has a maximally flat response over its passband.
Which circuit is used to detect FM-phone signals?
Frequency discriminator.
What causes a squelch circuit to function?
Presence of noise.
Where would you normally find a low-pass filter in a radio receiver?
In the AVC circuit.
In the Power Supply.
What is the primary purpose of the first IF amplifier stage in a receiver?
Selectivity.
A good crystal band-pass filter for a single-sideband phone would be?
2.1 KHz.
What is a product detector?
It uses a mixing process with alocally generated carrier.
What causes a squelch circuit to function?
Presence of noise.
What is cross-modulation interference?
Modulation from an unwanted signal heard in addition to the desired signal.
What factors should be considered when selecting an intermediate frequency?
Image rejection and selectivity.
Which statement is true regarding the filter output characteristics shown in Figure 3F16?
A is a low pass curve and D is a band stop curve.
Which circuit is used to detect FM-phone signals?
Frequency discriminator.
What makes a Digital Coded Squelch work?
Digital codes.
What is the term used to refer to the condition where the signals from a very strong station are superimposed on other signals being received?
Cross-modulation interference.
What is an advantage of a constant -k filter?
It has high attenuation of signals at frequencies far removed from the pass band.
What is the definition of detection in a radio receiver?
The recovery o intelligence from the modulated RF signal.
Pulse type interference to automobile radio receivers that appears related to the speed of the engine can often be reduced by:
Installing resistances in series with spark plug wires.
What are the three general groupings of filters?
High-pass, low-pass, and band-pass,
In a CTCSS controlled FM receiver, the CTCSS tone is filtered out after the:
Discriminator but before the audio section.
What is the digital signal processing term for noise subtraction circuitry?
Adaptive filtering and autocorrelation.
What is cross-modulation interference?
Modulation from an unwanted signal heard in addition to the desired signal.
What parameter must be selected when designing an audio filter using an op-amp?
Bandpass characteristics
What are the distinguishing features of a Butterworth filter?
It has a maximally flat response ver its passband.
What is the process of detection in a radio diode detector circuit?
Rectification and filtering of RF.
What radio circuit samples analog signals, records and processes them as numbers, then converts them back to analog signals?
The digital signal processing circuit.
How can ferrite beads be used to suppress ignition noise? Install them:
Install them in the primary and secondary ignition leads.
What makes a CTCSS squelch work?
Tones.
What is the primary purpose of the final IF amplifier stage iin a receiver?
Gain.
What is the definition of detection in a radio receiver?
The recovery of intelligence from the modulated RF signal.
In Figure 3F15 at what point in the circuit (labeled 1 through 4) could a DC voltmeter be used to monitor signal strength?
4
What is an m-derived filter?
A filter that uses a trap to attenuate undesired frequencies too near cutoff for a constant-k filter.
What is a product detector?
It uses a mixing process with a locally generated carrier.
What is the purpose of de-emphasis in the receiver audio stage?
When coupled with the transmitter pre-emphasis, flat audio and noise reduction is received.
What is the name of the condition that occurs when the signals of two transmitters in close proximity mix together in one or both of their final amplifiers, and unwanted signals at the sum and difference frequencies of the original transmissions are generated?
Intermodulation interference.
What is the deviation ratio for an FM phone signal having a maximum frequency deviation of plus or minus 5 kHz and accepting a maximum modulation rate of 3 kHz?
1.66
What kind of input signal could be used to test the amplitude linearity of a single-sideband phone transmitter while viewing the output on an oscilloscope?
A two-tone audio-frequency sine wave.
What is an important factor in pulse-code modulation using time-division multiplex?
Synchronization of transmit and receive clock pulse rates.
A battery with a terminal voltage of 12.5 volts is to be trickle-charged at a 0.5 A rate. What resistance should be connected in series with the battery to charge it from a 110-V DC line?
195 ohms.
Too much gain in a VHF receiver front end could result in this:
Susceptibility of intermodulation interference from nearby transmitters.
What are the principal frequencies that appear at the output of a mixer circuit?
The original frequencies that appear at the output of a mixer circuit.
A receiver selectivity of 10 KHz in the IF circuitry is optimum for what type of signals?
CW.
Which stage of a receiver primarily establishes its noise figure?
The RF stage.
In what stage of a VHF receiver would a low noise amplifier be most advantageous?
Front end RF stage.
A 12.6 volr, 8 ampere-hour battery is supplying power to a receiver that uses 60 watts and a RADAR system that uses 300 watts. How long will the battery last?
17 minutes or 0.3 hours.
The output of a separately-excited AC generator running at a constant speed can be controlled by:
The amount of field current.
What is meant by the term antenna bandwidth?
The frequency range over which an antenna can be expected to perform well.
Which of the following represents the best standing wave ratio (SWR)?
1:1.
To lengthen an antenna electrically, add a:
Coil.
A 6 volt battery with 1.2 ohms internal resistance is connected across two light bulbs in parallel whose resistance is 12 ohms each. What is the current flow?
0.83 amps.
What is the line current of a 7 horsepower motor operating on 120 volts at full load, a power factor of 0.8, and a 95% efficient?
57.2 amps.
A vertical 1/4 wave antenna receives signals:
Equally from all horizontal directions.
A radio frequency device that allows RF energy to pass through in one direction with very little loss but absorbs RF power in the oppsite direction is a:
Isolator.
At the ends of a half-wave antenna, what values of current and voltage exist compared to the remainder of the antenna?
Maximum voltage and minimum current.
An excited 1/2 wavelength antenna produces:
Both electro-magnetic and electro-static fields.
A ship RADAR unit uses 315 watts and a radio uses 50 watts. If the equipment is connected to a 50 ampere-hour battery rated at 12.6 volts, how long will the battery last?
1 hour 43 minutes.
Which of the following could cause a high standing wave ratio on a transmission line?
A detuned antenna coupler.
If a shunt motor running with a load has it shunt field opened, how would this affect the speed of the motor?
It will speed up.
The resonant frequency of a Hertz antenna can be lowered by:
Placing an inductance in series with the antenna.
If a marine radiotelephone receiver uses 75 watts of power and a transmitter uses 325 watts, how long can they both operate before discharging a 59 ampere-hour 12 volt battery?
1 1/2 hours.
A 3 horsepower, 100 V DC motor is 85% efficient when developing its rated output. What is the current?
26.300 amps.
Why is the value of the radiation resistance of an antenna important?
Knowing the radiation resistance makes it possible to match impedance for maximum power transfer?
When an emergency transmitter uses 325 watts and a receiver uses 50 watts, how many hours can a 12.6 volt, 55 ampere-hour battery supply full power to both units?
1.8 hours
What is meant by the term radiation resistance of an antenna?
An equivalent resistance that would dissipate the same amount of power as that radiated from an antenna.
What occurs if the load is removed from an oerating series DC motor?
It will accelerate until it falls apart.
What is the advantage of using a trap antenna?
It may be used for multiband operation.
An antenna radiates a primary signal of 500 watts output. If there is a 2nd harmonic output of 0.5 watt, what attenuation of the 2nd harmonic has occurred?
30 db.
To increase the resonant frequency of a 1/4 wavelength antenna?
Add a capacitor in series.
What is the current flowing through a 52-ohm line with an input of 1,872 watts?
6 amps.
What happens to the bandwidth of an antenna as it is shortened through the use of loading coils?
It is decreased.
There is an improper impedance match between a 30 watt transmitter and the antenna, with 5 watts reflected. How much power is actually radiated?
25 watts.
The expression “voltage regulation” as it applies to a shunt-wound DC generator operating at a constant frequency refers to:
Voltage fluctuations from load to no-load.
Why is the value of the radiation resistance of an antenna important?
Knowing the radiation resistance makes it possible to match impedances for maximum power transfer.
Nitrogen is placed in transmission lines to:
Prevent moisture from entering the line.
What is the effective radiated power of a repeater with 100 watts transmitter power output, 5 dB feedline loss, 4 dB duplexer and circulator loss, and 10 dB antenna gain?
126 watts
What radio navigation aid determines the distance from an aircraft to a selected VORTAC station by measurng the length of time the radio signal takes to travel to and from the station?
Distance Measuring Equipment (DME).
What is the frequency range of the ground-based Very-high-frequency Omnidirectional Range (VOR) stations used for aircraft navigation?
108.00 MHz to 117.95 MHz.
On runway approach, an ILS Localizer shows:
Deviation left or right of runway center line.
Referred to the fundamental frequency, a shorted stub line attached to the transmission line to absorb even harmonics could have a wavelength of:
1/4 wavelength
What is the effective radiated power of a repeater with 100 watts transmitter power output, 4 dB feedline loss, 3 dB duplexer and circulator loss, and 7 dB antenna gain?
100 watts.
The Ditance Measuring Equipment (DME) measures the distance from the aircraft to the DME ground station. This is referred to as:
The slant range.
All directions associated with a VOR station are related to:
Magnetic north.
What is the frequency range of the marker beacon system used to indicate an aircraft’s position during an Instrument Landing System (ILS) approach to an airport’s runway?
The outer, the middle, and the inner marker beacon’s carrier frequencies are all 75 MHz but the marker beacons are 95% tone-modulated at 400 MHz (outer), 1300 Hz (middle), and 300 Hz (inner).
What is the frequency range of the Distance Measuring Equipment (DME) used to indicate an aircraft’s slant range distance to a selected ground-based navigation station?
962 MHz to 1213 MHz.
The rate that the transmitted VOR variable signl rotates is equivalent to how many revolutiions per second?
30
Which of the following is a required omponent of an Instrument Landing System (ILS)?
Localizer: shows aircraft deviation hhorizontally from center of runway.
The amplitude modulated variable phase signal and the frequency modulated reference phase signal of a Very-high-frequency Omnidirectional Range (VOR) station used for aircraft navigation are synchronized so that both signals are in phase with each other at:___of the VOR station.
360 degreees North, magnetic bearing position.
What is the effective radiated power of a repeater with 50 watts transmitter power output, 4 dB feedline loss, 3 dB duplexer and circulator loss, and 6 dB antenna gain?
39.7 watts.
The majority of airborne Distance Measuring Equipment systems automatically tune their transmitter and receiver frequencies to the paired____/____channel.
VOR/LOC.
On runway approach, an IL Localizer shows:
Deviation left or right of runway center line.
What is the meaning of the term velocity factor of a transmission line?
The velocity of the wave on the transmission line divided by the velocity of light in a vacuum.
The Distance Measuring Equipment (DME) ground station has a built-in delay between reception of an interrogation and transmission of the reply to allow:
Operation at close range.
A perfect (no loss) coaxial cable has 7 dB of reflected power when the input is 5 watts. What is the output of the transmission line?
1 watt.
What is the main underlying operating principle of the Very-high-frequency Omnidirectional Range (VOR) aircraft navigational system?
A phase difference between two AC voltages may be used to determine an aircraft’s azimuth position in relation to a selected VOR station.
If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot transmission line fed by a 100 watt transmitter?
6 watts.
What is the main underlying operating principle of an aircraft’s Distance Measuring Equipment (DME)?
A measurable amount of time is required to send and receive a radio signal through the Earth’s atmosphere.
Choose the only correct statemet about the localizer beam system used by aircraft to find the centerline of a runway during an Instrument Landing System (ILS) approach to an airport. The localizer beam system:
Produces two amplitude modulated antenna patterns; one patern with an audio frequency of 90 Hz and one pattern with audio frequency of 150 Hz, one left of the runway centerline and one right of the runway centerline.
What type of encoding is used in an aircraft’s mode C transponder transmission to a ground station of the Air Traffic Control RADAR Beacon System (ATCRBS)?
Pulse position modulation.
Aircraft Emergency Locator Transmitters (ELT) operate on what frequencies?
121.5, 243 and 406 MHz.
What is the function of a commercial aircraft’s SELCAL installation? SELCAL is a type of aircraft communications______.
System where a ground-based transmitter can call a selected aircraft or group of aircraft without the flight crew monitoing the ground-station frequency.
What is a 1/2 digit on a DMM?
Partial extended accuracy on lower part of the range.
On an analog wattmeter, what part of the scale is most accurate and how much does that accuracy extend to the rest of the reading scale?
The accuracy is only at full scale, and that absolute number reading is carried through to the rest of the range. The upper 1/3 of the meter is the only truly calibrated part.
What type of antenna pattern is radiated from a ground station phased-array directional antenna when transmitting the PPM pulses in a Mode S interrogation signal of an aircraft’s Traffic alert and Collision Avoidance System 9TCAS) installation?
1030 MHz directional pattern.
Aviation services use predominately _____ microphones
Dynamic
What is the purpose of a shunt resistor used with an ammeter?
It is used to increase the ampere indicating range of the ammeter.
Which of the followiing contains AF voltmeter calibrated in dB and a sharp, internal 1000 Hz bandstop filter, both used in conjunction with each other to perform quieting tests?
SINAD meter.
What is meant by the term “night effect” when using an aircraft’s Automatic Direction Finding (ADF) equipment? Night effect refers to the fact that:
Non Directional Beacon (NDB) transmission can bounce-off the Earth’s ionosphere at night and be received at almost any direction.
What type of antenna is used in an aircraft’s Instrument Landing System (ILS) marker beacon installation?
A balanced loop reception antenna.
What type of antenna is used in an aircraft’s Very High Frequency Omnidirectional Range (VOR) and Localizer (LOC) installations?
Horizontally polarized omnidirection reception antenna.
What instrument may be used to verify proper radio antenna functioning?
An SWR meter.
What is a frequency standard?
A device used to produce a highly accurate reference frequency.
In addition to duplicating the functions of a mode C transponder, an aircraft’s mode S transponder can also provide:
Mid-Air collision avoidance capabiities.
What is the frequency range of an aircraft’s Very High Frequency 9VHF) communications?
118.000 MHz to 136.975 MHz (worldwide up to 151.975 MHz).
Some aircraft and avionics equipment operates with a prime power line frequency of 400 Hz. What is the principle advantage of a higher line frequency?
The magnetic devices in a 400 Hz power supply such as transformers, chokes and filters are smaller and lighter than those used in 60 Hz power supplies.
What is the purpose of a series multiplier resistor used with a voltmeter?
It is used to increase the voltage-indicating range of the voltmeter.
How is a frequency counter used?
To measure the time between events, or the frequency, which is the reciprocal of time.
What are the transmit and receive frequencies of an aircraft’s mode C transponder operating in the Air Traffic Control RADAR Beacon System (ATCRBS)?
Transmit at 1090 MHz, and receive at 1030 MHz
A 50 microampere meter movement has an internal resistance of 2,000 ohms. What applied voltage is required to indicate half-scale deflection?
0.05 volts.
Which of the following frequency standards is used as a time base standard by field technicians?
Rubidium Standard.
Typical airborne HF transmitters usually provide a nominal RF power output to the antenna of ___ watts, compared with ____ watts RF output from a typical VHF transmitter.
100, 20
What is a 1/2 digit on a DMM?
Partial extended accuracy on lower part of the range.
What equipment may be useful to track down EMI aboard a ship or aircraft?
Portable AM receiver.
What is the frequency range of an aircraft’s Automatic Direction Finding (ADF) equipment?
190 kHz to 1750 kHz.
What is the frequency range of an aircraft’s radio altimeter?
4250 MHz to 4350 MHz.
What is the function of a commercial aircraft’s SELCAL installation? SELCAL is a type of aircraft communications_____.
System where a ground-based transmitter can call a selected aircraft or group of aircraft without the flight crew monitoring the ground-station frequency.
What is the purpose of a series multiplier resistor used with a voltmeter?
It is used to increase the voltage-indicating range of the voltmeter.
What type of antenna is attached to an aircraft’s Mode C transponder installation and used to receive 1030 MHz interrogation signals from the Air Traffic Control Radar Beacon System (ATCRBS)?
An L-band monopole blade-type omnidirectional antenna.
What instrument is used to indicate high and low digital voltage states?
Logic probe.
What stage determines the maximum frequency response of an oscilloscope?
Vertical amplifier.
What does the horizontal axis of a spectrum analyzer display?
Frequency.
Which of the following answers is true?
The RF power reading on a CDMA radio is not accurate on an analog power meter.
When repairing circuit board assemblies it is most important to:
Wear safety glasses.
What is the 6th pair color code in a 25 pair switchboard cable as is found in building telecommunications interconnections?
Red/Blue, Blue/Red.
What instrument is commonly used by radio service technicians to monitor frequency, modulation, check receiver sensitivity, distortion, and to generate audio tones?
Service monitor.
What is the common method for determining the exact sensitivity specification of a receiver?
Measure the recovered audio for 12 dB of SINAD.
What is the proper way to cut plastic wire ties?
With flush-cut diagonal pliers and cut flush.
Why should you not use white or translucent plastic tie wraps on a radio tower?
UV radiation from the Sun deteriorates the plastic very quickly.
An oscilloscope can be used to accomplish all of the following except:
Measure velocity of light with the aid of a light emitting diode.
What test instrument can be used to display spurious signals in the output of a radio transmitter?
A spectrum analyzer.
What is the maximum FM deviation for voice operation of a normal wideband channel on VHF and UHF?
5.0 kHz
When soldering or working with CMOS electronics products or equipment, a wrist strap:
Must have less than 100,000 ohms of resistance to prevent static electricity.
What factors limit the accuracy, frequency response, and stability of an oscilloscope?
Sweep oscillator quality and deflection amplifier bandwidth.
What instrument is most accurate when checking antennas and transmission lines at the operating frequency of the antenna?
Frequency domain reflectometer
A “hot gas bonder” is used:
For non-contact melting of solder.
How does a spectrum analyzer differ from a conventional oscilloscope?
The oscilloscope is used to display electrical signals in the time domain while the spectrum analyzer is used to display electrical signals in the time domain.
What tet instrument can be used to display spurious signals in the output of a radio transmitter?
A spectrum analyzer.
The ideal method of removing insulation from wire is:
The thermal stripper.
What type of wire would connect an SSB automatic tuner to an insulated backstay?
GTO-15 high-voltage cable.
What common method used to program radios without using a “wired” connection?
Infra-red communication.
What tolerance off of plumb should a single base station radio rack be installed?
Just inside the bubble on a level.
What is most important when routing cables in a mobile unit?
Assuring radio or electronics cables do not interfere with the normal operation of the vehicle.
What does the vertical axis of a spectrum analyzer display?
Amplitude.
Can a P25 radio system be monitored with a scanner?
Yes, if the scanner has P25 decoding.
What is used to derease circuit loading when using an oscilloscope?
10:1 divider probe.
A communications technician would perform a modulation-acceptance bandwidth test in order to:
Determine the effective bandwidth of a communications receiver.
How might an installer verify correct GPS sentence to marine DSC VHF radio?
Look for latitude and longitude on the display.
A TDMA radio uses what to carry the multiple conversations sequentially?
Separate time slots.
The International Organization for Standardization has deloped a seven-level reference model for a packet-radio communications structure. The ____ level arranges the bits into frames and controls data flow.
Link layer.
What does the DSP not do in a modern DSP radio?
Control SWR.
What VHF channel is assigned for distress and calling?
16
The tachometer of a building’s elevator circuit experiences interference caused by the radio system nearby. What is a common potential “fix” for the problem?
Add a .01 µF capacitor across the motor/tachometer leads.
Name two types of spread spectrum systems used in most RF communications applications?
Direct Sequence and Frequency Hopping.
What CODEC is used in Pase 2 P25 radios?
AMBE
Which statement best describes the code used for GMDSS-DSC transmissions?
A 10 bit error correcting code starting with bits of data followed by a 3 bit error correcting code.
Maximum allowable frequency deviation for VHF marine radios is:
+/-5 kHz.
In a software-defined transceiver, what would be the best way for a technician to make a quick overall evaluation of the radio’s operational condition?
Use the built-in self-test feature
What principle allows mutiple conversations to be able to share one radio channel on a GSM channel?
Time Division Multiplex.
What are the two most-used PCS (Personal Communications Systems) coding techniques used to separate different calls?
CDMA and GSM.
What is a CODEC?
A coder/decoder IC or circuitry that converts a voice signal into a predetermined digital format for encrypted transmission.
A common method of programming portable or mobile radios is to use a:
A laptop computer.
What term escribes a wide-bandwidth communications system in which the RF carrier frequency varies according to some predetermined sequence?
Spread spectrum communication
The GSM (Global System for Mobile Communications) uses what type of CODEC for digital mobile radio system communicatons?
Regular-Pulse Excited (RPE).
Which of the folowing statements about SSB voice transmission is correct?
They normally use J3E emissions, which consists of one sideband and a suppressed carrier
The International Organization for Standardization has developed a seven-level reference model for a packet-radio communications structure. What level is responsible for the actual transmission of data and handshaking signals?
The physical layer.
What is a SDR?
Software Defined Radio.
What VHF Channel is used for Digital Selective Calling and acknowledgement?
70
What steps must be taken to activate the DSC emergency signaling function on a marine VHF?
Input of registered 9-digit MMSI.
What is the term used to escribe a spread spectrum commucations system where the center frequency of a conventional carrier is altered many times per second in accordance with a pseudo-random list of channels?
Frequency hopping.
Whih type of the following codes has gained the widest acceptance for exchange of data from one computer to another?
ASCII.
How might an installer verify correct GPS sentence to marine DSC VHF radio?
Look for latitude and longitude, plus speed, on VHF display.
Which is the code used for SITOR-A and B transmissions?
Each character consists of 7 bits with 4 “zeros” and 3 “ones”.
What is the channel used for VHF marine radio? spacing
25 kHz.
How many R-S flip-flops would be required to construct an 8 bit storage register?
8
The frequency of an AC signal can be divided electronically what type of digital circuit?
Bistable vibrator.
What is the name of the random-accessed semiconductor memory IC that must be refeshed periodically to maintain reliable data storage in its memory matrix/
DRAM - Dynamic Random-Access Memory.
What does the term “DAC” refer to in a microprocessor circuit?
Digital to analog converter
What is the purpose of a prescaler circuit?
Divides an HF signal so that a low-frequency counter can display the operating frequency.
How many bits of information can be stored in a single flip-flop circuit?
1
What wave form would appear on the voltage outputs at the collectors of an astable, multivibrator, common-emitter stage?
Square wave.
What is the name of the semiconductor memory IC whose digital data can be written or read, and whose memory word address can be accessed randomly?
RAM - Random-Access Memory.
In a microprocessor-controlled two-way radio, a “watchdog” timer:
Verifies that the microprocessor is executing the program
What integrated circuit device converts digital signals to analog signals?
DAC
What does the term “IO” mean within a microprocessor system?
Input-output.
What does the term “BCD” mean?
Binary coded decimal
What is a monostable multivibrator?
A circuit that can be switched momentarily to the opposite binary state and then returns after a set time to its original state.
What is the name of the semiconductor IC that has a fixed pattern of digital data stored in its memory matrix?
ROM - Read-Only Memory.
In a microprocessor, what is the meaning of the term “ALU”?
Arithmetical logic unit.
An R-S flip-flop is capable of doing all of the following except:
Operate in toggle mode with R-S inputs held constant and CLK initiated.
What is a bistable multivibrator circuit?
Flip-flop.
What is the name for a microprocessor’ sequence of commands and instructions?
Program.
What circuit interconnects the microprocessor with the memory and input/output system?
Data bus line.
In binary numbers, how would you note the quantity TWO?
0010
Which of the following is not part of a MCU processor?
Voltage Regulator
How many R-S flip-flops would be required to construct an 8 bit storage register?
8
What is the function of a decade counter digital IC?
Produce one output pulse for every ten input pulses.
How many fli-flops are required to divide a signal frequency by 4?
2
How many individual memory cells would be contained in a memory IC that has 4 data bus input/output pins and 4 address pins for connection to the address bus?
64
