Element 3 Sample Questions

Questions from each subelement of the FCC's Element 3 pool. Pick an answer to see whether you're right, how everyone else did, and why.

Element 3 exam guide

A Principles

When induced currents produce expanding magnetic fields around conductors in a direction that opposes the original magnetic field, this is known as:

Norton’s law.
Maxwell’s law.
Lenz’s law.
Gilbert's law.

Answer: C, Lenz’s law.. Lenz's law says the current induced by a changing magnetic flux always flows in the direction whose own magnetic field opposes that change. This is why a coil resists a change in current and why induced EMF carries a minus sign in Faraday's law (e = -N dΦ/dt). If a question describes induced effects that oppose the field or current that caused them, the answer is Lenz's law.

Corrosion resulting from electric current flow between dissimilar metals is called:

Oxygen starvation corrosion.
Stray current corrosion.
Galvanic corrosion.
Electrolysis.

Answer: C, Galvanic corrosion.. When two different metals touch in an electrolyte such as seawater, they form a small battery. Current flows from the more active (anodic) metal to the more noble (cathodic) one, and the anodic metal gradually dissolves. This is galvanic corrosion. It is why boats carry zinc sacrificial anodes and why bronze fittings shouldn't contact aluminum hulls.

By what factor must the voltage of an AC circuit, as indicated on the scale of an AC voltmeter, be multiplied to obtain the peak voltage value?

3.14
0.9
0.707
1.414

Answer: D, 1.414. An AC voltmeter reads RMS. For a sine wave, peak = RMS × √2 ≈ RMS × 1.414. For example, a 120 V reading means a peak of 120 V × 1.414 ≈ 170 V. Going the other way, RMS = peak × 0.707.

B Electrical math

A 500-ohm, 2-watt resistor and a 1500-ohm, 1-watt resistor are connected in parallel. What is the maximum voltage that can be applied across the parallel circuit without exceeding wattage ratings?

31.6 volts.
875 volts.
22.4 volts.
38.7 volts.

Answer: A, 31.6 volts.. Parallel resistors share the same voltage, so find each resistor's voltage limit from P = E²/R, or E = √(P × R). For the 500 Ω, 2 W part: √(2 W × 500 Ω) = √1000 ≈ 31.6 V. For the 1500 Ω, 1 W part: √(1 W × 1500 Ω) = √1500 ≈ 38.7 V. The lower limit governs: above 31.6 V the 500 Ω resistor would exceed 2 W.

What is the equivalent to the root-mean-square value of an AC voltage?

The DC voltage causing the same heating in a given resistor as the RMS AC voltage of the same value.
AC voltage is the square root of the average AC value.
The DC voltage causing the same heating in a given resistor at the peak AC voltage.
The AC voltage found by taking the square of the average value of the peak AC voltage.

Answer: A, The DC voltage causing the same heating in a given resistor as the RMS AC voltage of the same value.. The RMS value of an AC voltage is defined by heating effect. It is the DC voltage that delivers the same average power to a resistor. So 120 V RMS heats a resistor exactly as 120 V DC would. You compute it as the square root of the mean of the squared instantaneous values; for a sine wave, Vrms = 0.707 × Vpeak.

If a current of 3 amperes flows through a resistor connected to 90 volts, what is the resistance?

30 ohms.
93 ohms.
3 ohms.
270 ohms.

Answer: A, 30 ohms.. Resistance equals voltage divided by current. Here R = E / I = 90 V / 3 A = 30 Ω. As a check, 3 A × 30 Ω gives back the 90 V applied.

C Components

In a regulated power supply, what type of component will most likely be used to establish a reference voltage?

Pass Transistor.
Zener Diode.
Battery.
Tunnel Diode.

Answer: B, Zener Diode.. The reference in a regulated supply must stay fixed while input voltage and load vary. A Zener diode operated in reverse breakdown does that cheaply and indefinitely, clamping at its rated voltage. The regulator's error amplifier compares a sample of the output with that Zener voltage and corrects the control element accordingly.

What circuit might contain a SCR?

A light-dimming circuit.
Shunt across a transformer primary.
Filament circuit of a tube radio receiver.
Bypass capacitor circuit to ground.

Answer: A, A light-dimming circuit.. An SCR can be used for phase control. The gate fires it at a chosen point in each AC cycle, and it stays on until the current falls to zero. Firing later in the cycle delivers less average power to the load. That makes the SCR well suited to light dimmers and motor speed controls.

What is the piezoelectric effect?

Mechanical vibration of a crystal by the application of a voltage.
Reversed conduction states when a P-N junction is exposed to light.
The generation of electrical energy by the application of light.
Mechanical deformation of a crystal by the application of a magnetic field.

Answer: A, Mechanical vibration of a crystal by the application of a voltage.. Certain crystals, notably quartz, change shape slightly when a voltage is applied across them. An AC voltage makes the crystal vibrate mechanically. The effect also works in reverse: mechanical stress produces a voltage. A crystal vibrates most strongly at its natural resonant frequency, which is why quartz crystals are used to control oscillator frequency in radio transmitters and receivers.

D Circuits

How could voltage be greater across reactances in series than the applied voltage?

Resistance.
Capacitance.
Resonance.
Conductance.

Answer: C, Resonance.. At series resonance XL and XC cancel, so only R limits the current and I = E/R is large. That same current flows through each reactance, so V_L = I × XL. This can be many times E (a factor of Q). Example: E = 1 V, R = 10 Ω, XL = XC = 100 Ω gives I = 0.1 A and V_L = 10 V. The L and C voltages are 180° apart, so they cancel and the total still equals the source voltage.

Where is the external feedback network connected to control the gain of a closed-loop op-amp circuit?

Between the output and the differential inputs.
From output to the non-inverting input.
From output to the inverting input.
Between the differential inputs.

Answer: C, From output to the inverting input.. The feedback resistor runs from the output back to the inverting (−) input, which gives negative feedback. Any rise in output pulls the − input up and shrinks the difference between the inputs. This holds the gain at the resistor ratio. Inverting and non-inverting amplifiers both use this connection; they differ only in which input the signal drives.

A circuit that compares the output of a voltage-controlled oscillator (VCO) to a frequency standard and produces an error voltage that is then used to adjust the capacitance of a varactor diode used to control frequency in that same VCO is called what?

Differential voltage amplifier.
Variable frequency oscillator.
Doubly balanced mixer.
Phase-locked loop.

Answer: D, Phase-locked loop.. This describes a phase-locked loop. A phase detector compares the VCO, usually after a divider, with a stable reference. A loop filter turns the difference into a DC error voltage, which biases a varactor to retune the VCO until it locks to the reference. With a ÷N divider in the loop, f_out = N × f_ref, which is the basis of PLL synthesizers.

E Digital logic

How many R-S flip-flops would be required to construct an 8 bit storage register?

Answer: D, 8. Each R-S flip-flop holds one bit. An 8-bit storage register therefore needs 8 flip-flops, one per bit position, typically loaded in parallel by a common clock or enable line. Eight flip-flops can together hold any of 2⁸ = 256 different values.

What is an astable multivibrator?

A circuit that alternates between two stable states.
A circuit that alternates between a stable state and an unstable state.
A circuit that alternates between two unstable states.
A circuit set to block either a 0 pulse or a 1 pulse and pass the other.

Answer: C, A circuit that alternates between two unstable states.. An astable (free-running) multivibrator has no state it can rest in. Each output state is only temporary, held until an RC network times out, and then the circuit flips to the other. It switches back and forth continuously with no trigger, making it a square-wave oscillator or clock. Count the stable states: astable 0, monostable 1, bistable 2.

What integrated circuit device converts an analog signal to a digital signal?

Answer: B, ADC. An ADC (analog-to-digital converter) samples a continuously varying voltage and outputs a binary number proportional to it. Read the name in order: analog in, digital out. Its resolution is set by the bit count; for example, 8 bits gives 2⁸ = 256 levels. It is used in DSP radios, digital meters and audio digitizing.

F Receivers

What is meant by the term noise figure of a communications receiver?

The level of noise entering the receiver from the antenna.
The ability of a receiver to reject unwanted signals at frequencies close to the desired one.
The relative strength of a received signal 3 kHz removed from the carrier frequency.
The level of noise generated in the front end and succeeding stages of a receiver.

Answer: D, The level of noise generated in the front end and succeeding stages of a receiver.. Noise figure measures how much noise the receiver itself adds, starting at the front end and continuing through later stages. It is the ratio of input SNR to output SNR, expressed in dB. A perfect, noiseless receiver would have a 0 dB noise figure. The lower the noise figure, the weaker the signal the receiver can hear.

What is the process of detection in a radio diode detector circuit?

Rectification and filtering of RF.
Breakdown of the Zener voltage.
The change of reactance in the diode with respect to frequency.
Mixing with noise in the transition region of the diode.

Answer: A, Rectification and filtering of RF.. In an AM diode detector, the diode conducts on only one polarity of the RF or IF wave. This half-wave rectification leaves pulses whose peaks follow the modulation envelope. An RC filter then removes the RF component and keeps the audio-rate envelope. Detection here therefore equals rectification plus filtering.

What makes a CTCSS squelch work?

Noise.
Digital codes.
Absence of noise.
Tones.

Answer: D, Tones.. CTCSS (Continuous Tone-Coded Squelch System, often called PL) transmits one continuous subaudible tone, from about 67 Hz to 254 Hz, along with the voice. The receiver's tone decoder unmutes the audio only when it hears its programmed tone, and a high-pass filter keeps the tone out of the speaker. This lets several user groups share one channel without hearing each other.

G Transmitters

The class AB amplifier output is present for what portion of the input cycle?

Exactly 180 degrees.
360 degrees
Less than 180 degrees.
More than 180 but less than 360 degrees.

Answer: D, More than 180 but less than 360 degrees.. Class AB is biased slightly above cutoff, so each device conducts for more than half the input cycle but not all of it: more than 180° and less than 360°. In push-pull, the overlap where both devices conduct removes Class B's crossover distortion. Efficiency stays better than Class A, which makes Class AB the usual linear amplifier for SSB.

What is the total bandwidth of a FM phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency?

8 kHz.
5 kHz.
16 kHz.
3 kHz.

Answer: C, 16 kHz.. Carson's rule estimates the occupied bandwidth of an FM signal: BW = 2(Δf + fm) = 2(5 kHz + 3 kHz) = 16 kHz. Significant sidebands extend roughly the deviation plus the highest modulating frequency on each side of the carrier. The factor of 2 covers both sides.

How can intermodulation interference between two transmitters in close proximity often be reduced or eliminated?

By installing a band-pass filter in the antenna feed line.
By installing a terminated circulator or ferrite isolator in the feed line to the transmitter and duplexer.
By installing a low-pass filter in the antenna feed line.
By using a Class C final amplifier with high driving power.

Answer: B, By installing a terminated circulator or ferrite isolator in the feed line to the transmitter and duplexer.. Intermodulation between nearby transmitters happens when one station's signal couples back into the other's final amplifier. There the non-linear stage mixes the two signals and radiates new products. A terminated ferrite circulator or isolator passes outgoing power to the antenna and duplexer. It routes any incoming signal into a dummy-load termination, so the energy never reaches the amplifier to be mixed.

H Modulation

In an FM-phone signal, what is the term for the maximum deviation from the carrier frequency divided by the maximum audio modulating frequency?

Deviation index.
Deviation ratio.
Modulation index.
Modulation ratio.

Answer: B, Deviation ratio.. Deviation ratio = maximum allowed deviation ÷ maximum audio modulating frequency. Marine VHF FM, for example, uses 5 kHz ÷ 3 kHz ≈ 1.67. It is a fixed design figure for the whole system. The modulation index, by contrast, uses the actual deviation and actual tone at any moment.

What does a two-tone test illustrate on an oscilloscope?

Linearity of a SSB transmitter.
Sideband suppression.
Percentage of frequency modulation.
Frequency of the carrier phase shift.

Answer: A, Linearity of a SSB transmitter.. A two-tone test makes the SSB output envelope swing repeatedly from zero to full peak power. This exercises the amplifiers over their whole range. If the stages are linear, the scope shows clean, rounded, symmetric lobes. Flat-topping reveals overdrive or compression, and distortion near the zero crossings reveals improper bias. The same pattern is also used to read peak envelope power.

What is the name of the type of modulation in which the modulating signal varies the duration of the transmitted pulse?

Frequency modulation.
Pulse-width modulation.
Pulse-height modulation.
Amplitude modulation.

Answer: B, Pulse-width modulation.. When the modulating signal changes how long each pulse lasts, the scheme is pulse-width modulation, also called pulse-duration modulation (PDM). Each pulse type is named for what varies: amplitude gives PAM, width or duration gives PWM, timing gives PPM, and rate gives pulse-frequency modulation.

I Power sources

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?

95 ohms.
300 ohms.
195 ohms.
None of these.

Answer: C, 195 ohms.. The series resistor must drop the difference between the line and battery voltages at the charging current. Voltage across the resistor = 110 V − 12.5 V = 97.5 V. R = E / I = 97.5 V / 0.5 A = 195 Ω. The resistor dissipates P = 97.5 V × 0.5 A ≈ 49 W, so its power rating must be at least that.

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?

6.0 amps.
1.0 amps.
0.57 amps.
0.83 amps.

Answer: D, 0.83 amps.. Two equal 12 Ω bulbs in parallel combine to 12 Ω / 2 = 6 Ω. The battery's 1.2 Ω internal resistance is in series with that combination, so the total is 7.2 Ω. Then I = E / R = 6 V / 7.2 Ω ≈ 0.83 A. Always include internal resistance in series with the external load.

The expression “voltage regulation” as it applies to a shunt-wound DC generator operating at a constant frequency refers to:

Voltage output efficiency.
Voltage in the secondary compared to the primary.
Rotor winding voltage ratio
Voltage fluctuations from load to no-load.

Answer: D, Voltage fluctuations from load to no-load.. Voltage regulation describes how much a generator's terminal voltage changes between no load and full load. It is usually stated as a percentage: (E no-load − E full-load) / E full-load × 100. In a shunt-wound generator, voltage sags under load because of armature resistance drop and a weakening field. A small percentage means good regulation.

J Antennas

What happens to the bandwidth of an antenna as it is shortened through the use of loading coils?

It becomes flat.
It is increased.
No change occurs.
It is decreased.

Answer: D, It is decreased.. A physically short antenna that is brought to resonance with a loading coil has a low radiation resistance and a high Q. Higher Q means a narrower bandwidth: the SWR rises quickly as you tune away from the resonant frequency. That narrow bandwidth is the trade-off for short, coil-loaded mobile and marine HF whips. They often need retuning when you change frequency.

What determines the velocity factor in a transmission line?

The termination impedance.
The line length.
Dielectrics in the line.
The center conductor resistivity.

Answer: C, Dielectrics in the line.. The insulating material between the conductors sets how fast the wave travels. Approximately, VF = 1 / √εr, where εr is the dielectric constant. Solid polyethylene (εr ≈ 2.3) gives about 0.66, foam gives about 0.8, and air (εr ≈ 1) gives close to 1. The higher the dielectric constant, the slower the wave.

What is the effective radiated power of a repeater with 75 watts transmitter power output, 5 dB feedline loss, 4 dB duplexer and circulator loss, and 6 dB antenna gain?

237 watts.
37.6 watts.
23.7 watts.
150 watts.

Answer: B, 37.6 watts.. Net system gain = 6 dB − 5 dB − 4 dB = −3 dB. As a power ratio, 10^(−3/10) ≈ 0.501, so ERP = 75 W × 0.501 ≈ 37.6 W. When the losses exceed the antenna gain, ERP falls below the transmitter output; −3 dB is about half power.

K Aircraft

Which of the following is a required component of an Instrument Landing System (ILS)?

Distance Measuring Equipment: shows aircraft distance to VORTAC station.
VHF Communications: provide communications to aircraft.
Altimeter: shows aircraft height above sea-level.
Localizer: shows aircraft deviation horizontally from center of runway.

Answer: D, Localizer: shows aircraft deviation horizontally from center of runway.. An ILS has two core radio parts. The localizer gives left/right guidance onto the runway centerline at 108.10–111.95 MHz. The glideslope gives vertical guidance at 329.15–335.00 MHz. Marker beacons or DME add distance checkpoints. Without a localizer there is no ILS approach, while a localizer-only approach is still possible.

Choose the only correct statement about an aircraft’s Automatic Direction Finding (ADF) equipment.

Only a single omnidirectional sense antenna is required to receive an NDB transmission and process the signal to calculate the aircraft’s bearing to the selected ground station.
An aircraft’s ADF transmission exhibits primarily a line-of-sight range to the ground-based target station and will not follow the curvature of the Earth.
All frequencies in the ADF’s operating range except the commercial standard broadcast stations (550 to 1660 kHz) can be utilized as a navigational Non Directional Beacon (NDB) signal.
An aircraft’s ADF antennas can receive transmissions that are over the Earth’s horizon (sometimes several hundred miles away) since these signals will follow the curvature of the Earth.

Answer: D, An aircraft’s ADF antennas can receive transmissions that are over the Earth’s horizon (sometimes several hundred miles away) since these signals will follow the curvature of the Earth.. ADF works on LF and MF, where signals travel mostly as ground waves that bend to follow the Earth's surface. So an aircraft can receive an NDB or AM broadcast station far beyond line of sight, sometimes hundreds of miles away. VHF navigation aids cannot do this. The receiver needs a loop antenna to find direction plus a sense antenna. An ADF only receives; it does not transmit.

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)?

A folded dipole reception antenna.
An internally mounted, mechanically rotatable loop antenna.
An electronically steerable phased-array directional antenna.
An L-band monopole blade-type omnidirectional antenna.

Answer: D, An L-band monopole blade-type omnidirectional antenna.. A transponder receives on 1030 MHz and replies on 1090 MHz, both in L-band. At about 1 GHz a quarter wavelength is only about 7 cm, so a short monopole in a swept blade housing on the belly works well. Its vertical omnidirectional pattern lets it hear interrogators in any direction around the aircraft. The ground radar decides direction, so the aircraft antenna doesn't need to.

L Installation, maintenance & repair

What is a frequency standard?

A well-known (standard) frequency used for transmitting certain messages.
A device used to produce a highly accurate reference frequency.
A device used to generate wide-band random frequencies.
A device for accurately measuring frequency to within 1 Hz.

Answer: B, A device used to produce a highly accurate reference frequency.. A frequency standard is an oscillator built to produce one very accurate and stable reference frequency, such as 10 MHz. Counters, signal generators and transmitters are calibrated against it. Examples run from oven-controlled crystal oscillators up to rubidium, cesium and GPS-disciplined standards. It is the yardstick, not the measuring instrument.

How does a spectrum analyzer differ from a conventional oscilloscope?

The oscilloscope is used to display electrical signals while the spectrum analyzer is used to measure ionospheric reflection.
The oscilloscope is used to display electrical signals in the frequency domain while the spectrum analyzer is used to display electrical signals in the time domain.
The oscilloscope is used for displaying audio frequencies and the spectrum analyzer is used for displaying radio frequencies.
The oscilloscope is used to display electrical signals in the time domain while the spectrum analyzer is used to display electrical signals in the frequency domain.

Answer: D, The oscilloscope is used to display electrical signals in the time domain while the spectrum analyzer is used to display electrical signals in the frequency domain.. An oscilloscope plots amplitude against time (the time domain), so you see waveform shape, period and rise time. A spectrum analyzer sweeps across frequency and plots amplitude against frequency (the frequency domain). It shows each carrier, sideband, harmonic and spur as a separate peak.

What instrument is commonly used by radio service technicians to monitor frequency, modulation, check receiver sensitivity, distortion, and to generate audio tones?

Spectrum analyzer.
Service monitor.
DMM.
Oscilloscope.

Answer: B, Service monitor.. A service monitor, also called a communications test set, packs several instruments into one box. It typically includes an RF signal generator, frequency counter, deviation/modulation meter, SINAD and distortion meter, and audio tone generator, often with a built-in scope or spectrum display. That lets a technician fully test a two-way radio's transmitter and receiver at the bench.

M Communications technology

What term describes a wide-bandwidth communications system in which the RF carrier frequency varies according to some predetermined sequence?

SITOR.
Amplitude compandored single sideband.
Time-domain frequency modulation.
Spread spectrum communication.

Answer: D, Spread spectrum communication.. In spread spectrum the transmitted signal occupies a much wider bandwidth than the information needs. In this case the carrier frequency follows a predetermined pseudo-random sequence, and a receiver that knows the sequence follows it. The spreading resists interference and jamming and lets many users share a band.

Which of the following codes has gained the widest acceptance for exchange of data from one computer to another?

ASCII.
Baudot.
Morse.
Gray.

Answer: A, ASCII.. ASCII (American Standard Code for Information Interchange) is a 7-bit code defining 128 letters, digits, punctuation marks and control characters. It became the common language for computer-to-computer data exchange. Its successor, Unicode in UTF-8 form, keeps the ASCII codes as its first 128 characters, so ASCII remains the base of text data.

What does the DSP not do in a modern DSP radio?

Control frequency.
Control SWR.
Control modulation.
Control detection.

Answer: B, Control SWR.. In a modern DSP radio, the signal processor handles signal-path work: tuning and frequency synthesis or digital down-conversion, generating the modulation, and detecting or demodulating the received signal. SWR depends on how well the antenna and feed line match the transmitter output. Only a physical matching network such as an antenna tuner can change it. The DSP can monitor SWR, but it cannot control it.

N Marine

What VHF Channel is used for Digital Selective Calling and acknowledgement?

Answer: D, 70. 47 CFR 80.369(e)(2) makes 156.525 MHz (channel 70) the VHF frequency for distress, safety and general-purpose DSC calls. DSC sends short digital alerts and acknowledgments on channel 70, then traffic moves to a voice channel such as 16. Voice is not permitted on channel 70. Under 80.369(e)(4), DSC-equipped vessels may send their initial distress call on channel 70.

What might contribute to apparent low voltage on marine SSB transmitting?

Antenna mismatch.
Blown red fuse.
Too much grounding.
Blown black negative fuse.

Answer: D, Blown black negative fuse.. Some SSB power cables have a fuse in both the red positive lead and the black negative lead. If the negative fuse blows, the radio may still run because return current finds a stray path through the coax shield, chassis or RF ground. That path has high resistance, so under transmit load the radio sees a sagging supply voltage. A blown negative-lead fuse therefore shows up as low voltage rather than a dead radio.

Which of the following statements concerning satellite EPIRBs is true?

Once activated, these EPIRBs transmit a signal for use in identifying the vessel and for determining the position of the beacon.
The coded signal only identifies the vessel’s name and port of registry.
If the GMDSS Radio Operator does not program the EPIRB, it will transmit default information such as the follow-on communications frequency and mode.
The coded signal identifies the nature of the distress situation.

Answer: A, Once activated, these EPIRBs transmit a signal for use in identifying the vessel and for determining the position of the beacon.. An activated 406 MHz satellite EPIRB sends a digital burst carrying a unique beacon identity, often based on the ship's MMSI, which links to the owner's registration. Cospas-Sarsat satellites find its position from the Doppler shift, or from GNSS position data in the message. So one signal both identifies the vessel and lets rescuers locate the beacon.

O Radar

The RADAR range in nautical miles to an object can be found by measuring the elapsed time during a RADAR pulse and dividing this quantity by:

12.346 µs.
1.073 µs.
0.87 seconds.
1.15 µs.

Answer: A, 12.346 µs.. Radio energy covers 1 nautical mile (1852 m) in about 6.173 µs. A radar pulse must travel out to the target and back, so each nautical mile of range adds 12.346 µs of elapsed time, the 'radar mile'. Range (nmi) = elapsed time ÷ 12.346 µs. For example, 123.46 µs ÷ 12.346 µs = 10 nmi.

We are looking at a target 25 miles away. When a RADAR is being operated on the 25 mile range setting what is the most appropriate pulse width and pulse repetition rate?

0.05 s PW and 2,000 pps.
0.01 s PW and 500 pps.
1.0 s PW and 500 pps.
0.25 s PW and 1,000 pps.

Answer: C, 1.0 s PW and 500 pps.. A target 25 mi away returns a weak echo, so energy on target matters most. A 1.0 µs pulse carries four times the energy of a 0.25 µs pulse at the same peak power. The 500 pps rate leaves a 2,000 µs interval, about 160 mi at 12.36 µs per nmi. Every echo therefore returns well before the next pulse. ("s" here means µs.)

Exposure to microwave energy from RADAR or other electronics devices is limited by U.S. Health Department regulations to _______ mW/centimeter.

0.05
0.5
5.0
0.005

Answer: C, 5.0. The federal health limit for microwave exposure used in radar safety is a power density of 5.0 mW/cm². The same 5 mW/cm² figure appears in the federal microwave-oven leakage standard. It also matches the FCC occupational exposure limit at microwave frequencies. Learn it as a power density in milliwatts per square centimeter.

P Satellite

What is the main function of the COSPAS-SARSAT satellite system?

Monitor 121.5 MHz for voice distress calls.
Monitor 1635 MHz for coded distress calls.
Monitor 2197.5 kHz for hexadecimal coded DSC distress messages.
Monitor 406 MHz for distress calls from EPIRBs.

Answer: D, Monitor 406 MHz for distress calls from EPIRBs.. COSPAS-SARSAT is the international satellite search-and-rescue system for distress beacons: EPIRBs on ships, ELTs on aircraft and PLBs carried by people. Its satellites listen on 406 MHz for digital beacon bursts. Each burst carries a unique ID, registered in the US with NOAA. The satellites relay the bursts to ground stations (LUTs) and on to mission control centers. Satellite processing of 121.5 MHz ended in 2009.

When INMARSAT-B and INMARSAT-C terminals are compared:

INMARSAT-B antennas are bulkier but omni-directional, while INMARSAT-C antennas are smaller and parabolic, for aiming at the satellite.
INMARSAT-C antennas are smaller but omni-directional, while INMARSAT-B antennas are parabolic for lower gain.
INMARSAT-C antennas are small and omni-directional, while INMARSAT-B antennas are larger and directional.
INMARSAT-B antennas are parabolic and smaller for higher gain, while INMARSAT-C antennas are larger but omni-directional.

Answer: C, INMARSAT-C antennas are small and omni-directional, while INMARSAT-B antennas are larger and directional.. Inmarsat-C needs only a few hundred bits per second, so a small, low-gain omnidirectional antenna is enough. It needs no aiming or stabilization. Inmarsat-B carried voice and 64 kbps data, which required a high-gain parabolic dish. That dish is larger and heavier, and it must be steered to track the satellite as the ship moves. The general rule: a higher data rate needs more antenna gain, and more gain means a directional antenna.

The GPS transmitted frequencies are:

946.2 MHz and 1226.6 MHz.
2245.4 and 2635.4 MHz.
1227.6 MHz and 1575.4 MHz.
1626.5 MHz and 1644.5 MHz.

Answer: C, 1227.6 MHz and 1575.4 MHz.. GPS satellites transmit in the L band. L1 at 1575.42 MHz carries the civil C/A code. L2 at 1227.60 MHz carries the precision code and, on newer satellites, the civil L2C signal. Receivers that compare the two frequencies can correct for ionospheric delay. Modernized satellites also add L5 at 1176.45 MHz, but L1 and L2 are the classic pair to remember.

Q Safety

What class of fire is one that is caused by an electrical short circuit and what is the preferred substance used to extinguish that type of fire?

FE29.
FE31.
FE28.
FE30.

Answer: D, FE30.. A fire caused by an electrical short circuit involves energized equipment, which makes it a Class C fire. The extinguishing agent must not conduct electricity, so carbon dioxide (CO2) or a dry chemical (BC or ABC) extinguisher is preferred. Water or foam can electrocute the user. Figure FE30 shows the Class C rating with a nonconductive agent. De-energize the equipment first if you can do it safely.

What is a GFI electrical socket used for?

To increase the current capacity of the socket.
To prevent electrical shock by sensing ground path current and shutting the circuit down.
To prevent children from sticking objects in the socket.
As a gold plated socket.

Answer: B, To prevent electrical shock by sensing ground path current and shutting the circuit down.. A ground-fault interrupter (GFI or GFCI) compares the current in the hot and neutral wires. If they differ by more than about 5 mA, some current is leaking to ground, possibly through a person. The device then opens the circuit within a fraction of a second, before the shock becomes dangerous. Use GFI outlets near water and on damp shop benches.

Compliance with MPE, or Maximum Permissible Exposure to RF levels (as defined in FCC Part 1, OET Bulletin 65) for “controlled” environments, are averaged over _ minutes, while “uncontrolled” RF environments are averaged over minutes.

15, 1.
30, 6.
6, 30.
1, 15.

Answer: C, 6, 30.. The FCC's Part 1 RF exposure rules, explained in OET Bulletin 65, set different averaging periods for MPE. Exposure in occupational/controlled environments is averaged over 6 minutes. Exposure in general population/uncontrolled environments is averaged over 30 minutes. Controlled settings involve workers who know about the exposure and can limit it. The uncontrolled public also gets limits about five times lower.