M13 - 04 Communications
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- Created on: 13-03-24 14:29
What is the propagation speed of radio waves in free space?
300,000 KM/s
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How is the frequency of alternating current calculated?
1/T
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What is the elapsed time of one period of a wave known as?
T
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How is the wavelength (λ) calculated?
c (Speed of radio wave) x T
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What is obtained when superimposing the 1st, 3rd and 5th harmonic?
Rectangular waveform
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What is formed when all harmonics are added together?
Sawtooth waveform
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Which frequency band is used for a carrier wave?
Radio Frequency (RF)
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What is the frequency range for RADAR band C?
3.9 GHz - 6.2 GHz
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What is the frequency range for RADAR band X?
5.2 GHz - 10.9 GHz
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What frequency range contains HF?
2 - 30 MHz
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What frequency range contains VHF?
118 - 137 MHz
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What frequency range contains UHF?
225 - 400 MHz
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What are Oscillating and Resonant systems used for?
Generation and selective amplification or damping of periodic processes
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What is a mechanical oscillator?
A mass which displaces against a spring or earths gravitational force
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How is an open oscillation circuit that radiates energy as an electromagnetic wave known?
Antenna
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What is a cavity resonator?
An arrangement of an electrical oscillator where energy cycles only within the system
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At frequencies below the oscillator frequency (Fo), what is true of the circuit?
Inductive
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At frequencies above the oscillator frequency (Fo), what is true of the circuit?
Capacitive
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What is the quality factor/figure of merit (Q)?
Ratios of currents (I_c & I_l) Ito the externally applied current, expressed with no units.
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How is the bandwidth affected by a high Q factor?
Narrow bandwidth
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How is the bandwidth affected by a low Q factor?
Wide bandwidth
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If the Q factor and frequency are known, how can the bandwidth be calculated?
Frequency / Q factor
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What are the 2 broad categories of radio equipment?
Transmitting & Receiving
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What stage of the audio transmitter is responsible for placing the audio intelligence on the RF signal?
Modulator
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What are the four essential parts of an AM transmitter?
Oscillator, Amplification, Modulator and a power supply
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How is the oscillator that is used to generate the basic transmitter RF?
Master oscillator
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What are the two main types of microphone used in aviation?
Carbon and Dynamic
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What is normally incorporated in the microphone case of a dynamic microphone, due to its voltage being small?
A pre-amplifier
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How is the resistance within a carbon microphone affected by sound waves?
Sound waves compress the carbon granules which causes the resistance to change according to the amplitude and frequency of the sound.
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What are the major sub parts of a transmitter?
Oscillator, Modulator, Power amplifier and an antenna
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What sort of feedback does an oscillator require?
Positive feedback loop
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In order for the oscillation amplitude to be maintained, what ring amplification is required?
Equal to 1
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In order for automatic oscillation, what conditions are required?
Ring amplification equal to or greater than 1
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What are the names of the three types of L-C oscillator?
Meissner, Colpitts and Hartley
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Why are crystals used in oscillator circuits?
High frequency stability and excellent Q-factor
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How many resonant frequencies do crystals have?
Series and parallel
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What is a frequency synthesizer?
A module in which frequencies generated by reference oscillator are mixed to produce output frequencies
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What does a phase comparator do within a frequency synthesizer?
Compares the reference frequency with the frequency generated by the voltage controlled oscillator (VCO)
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Within a frequency synthesizer, what is a VCO?
A VCO is a controllable frequency oscillator that regulates frequency with voltage
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When does superimposing occur?
When 2 or more AC voltages meet in linear components
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What sort of components are required for modulation?
Non-linear components
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What is the bandwidth in AM?
The frequency range a transmission requires to transmit the entire side bands.
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How is the power in sidebands calculated?
Carrier power/2 * modulation index
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What are the advantages of Single Side Band (SSB) over AM?
Narrow bandwidth, less energy required, less distortion
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What is the disadvantage of Single Side Band (SSB)?
Accurate and stable frequency required
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What determines the difference between the highest and lowest frequencies in FM modulation?
Modulation index
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What are the variables for pulse modulation (PM)?
Amplitude, length, phase and code
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What is the advantage of Quadruple Phase Shift Keying (QPSK) compared to Binary Phase Shift Keying (BPSK)?
The bandwidth efficiency (Ideally) is higher by a factor of 2
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What is the advantage of a transistor modulator circuit compared to a diode modulator circuit?
A transistor modulator circuit has additional amplification of the modulated RF signal
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A balance modulator uses 4 diodes for amplitude modulation with SSB, what is true in regards to the diodes if complete suppression of the carrier is required?
All four diodes must be identical
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What are the two conductor types of RF lines?
Symmetric and asymmetric cable
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What does line impedance depend on?
Material and physical dimensions of the cable
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What is line impedance independent of?
Length
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When is maximum power transfer in an RF line?
When the impedance of the aerial and line is matched
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What is the Standing Wave Ratio (SWR)?
The ratio of the maximum voltage (or current) to the minimum voltage (or current) of the standing wave
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What is the minimum length of a dipole antenna?
1/2 wavelength
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What element of an electromagnetic wave determines the polarization of an antenna?
Direction of E field
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What is the minimum length of a rod antenna on an aircraft?
1/4 wavelength
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What is another name for a rod antenna?
Marconi antenna
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What is antenna gain (G)?
The increase in power in a direction by directional radiation compared to a reference antenna
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How is an antenna electrically tuned?
Compensation of the reactance by a chance of inductance or capacitance
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What is a ground wave?
The part of a wave that moves outward in contact with the ground
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What surface does a ground wave propagate best across?
Salt water
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Where are low frequency transmitters usually placed?
As close to the edge of the ocean as practical
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What is a wave skip zone?
The area between the first sky wave reception and the end of ground wave reception
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What is the critical angle in terms of wave propagation?
The angle made by group 2 rays in which any ray that leaves the antenna at an angle greater than this will penetrate the ionosphere
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What determines the critical frequency of a sky wave?
Highest frequency that can be sent directly upwards and still refract back to earth.
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How is fading of sky waves prevented?
Placing two antennas a wavelength apart and feed two separate receivers, this is known as diversity reception.
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What is the main advantage of a superhetrodyne receiver?
Desired receiving frequencies are changed into an intermediate frequency for better selectivity
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How many frequencies does the mixer within a superhetrodyne receiver produce?
4. Incoming RF, local oscillator, sum of incoming signal and local oscillator signal and the difference of these signals
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Within an IF amplifier, how is image frequency interference removed?
A high intermediate frequency is used so that the image frequency lies outside of the bandwidth of the input circuit.
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How is adjacent channel interference removed?
A low intermediate frequency that is not too high is used compared with the channel spacing
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What is the detector within a superhetrodyne receiver also known as?
Demodulator
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What is the difference between AM and FM demodulation?
AM demodulation uses non-linear frequency dependent characteristics and FM uses linear
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What is automatic gain control in a receiver?
Amplification of RF and IF stages automatically to maintain a stable input signal amplitude
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What is the squelch threshold within a receiver?
When an input signal is below the threshold, the demodulator output is not amplified in the audio amplifier.
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What does a Beat Frequency Oscillator (BFO) do?
Makes unmodulated or keyed transmissions available, oscillation occurs at a frequency which is 1020 Hz above or below the IF.
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What sort of amplifier is used in the audio amplifier?
Single stage class A
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What does the voice only button on an audio selector control panel do?
Allows the suppression of identification signals by a filter
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How is interference between multiple receivers suppressed in an audio circuit?
High isolating resistances installed in the ASP
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What is the purpose of the audio management unit (AMU)?
Acts as an interface between the users and the various radio communication and navigation systems
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On an audio control panel, how many radio systems can be selected at a time for transmission?
1
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What are the types of interphone within the interphone system?
Flight, Cabin, and Service Interphone
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To prevent the entire flight or cabin interphone system shorting due to dirt in any of the service interphone jacks, how can it be deselected?
Service interphone can be deselected by moving the service interphone switch to OFF
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What has the highest priority on the Passenger Address (PA) system?
Manual PA announcements
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What has the lowest priority on the Passenger Address (PA) system?
Boarding music
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What does the AM button on the Radio Management Panel (RMP) do?
Controls the selection of AM mode for the HF transceivers, by default Single Side Board (SSB) is selected.
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What is the NAV guarded push-button on the Radio Management Panel (RMP) for?
Allows the radio nav systems to be selected in backup mode only (when the FMGCs fail)
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What is the frequency band for VHF?
118-137 MHz
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What is VHF channel spacing?
25 kHz and 8.33 kHz
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What type of modulation does VHF use?
AM
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How should VHF COM systems be polarised?
Vertical
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For flights under Instrument Flight Rules (IFR), how many VHF transceivers must be equipped?
2
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How is the VHF system operated in the case of an emergency?
28V DC from batteries
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How is ice accumulation on the VHF antenna prevented?
The antenna is connected to the aircraft anti-icing system
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What is the base impedance of the VHF antenna?
50 ohms
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What is the frequency range of the HF system?
2 - 30 MHz
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What is the name given to the area in which radio contact is not possible for the HF system?
Skip zone
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How can the tuning process of the HF system be recognised?
1 kHz tone
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What is side tone in a HF system a good indication of?
Good transmitter signal strength
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When the Key Interlock Circuit of the HF system is interrupted, what happens?
KEY INTERLOCK fault light, absense of side tone.
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What is the purpose of the HF antenna coupler?
Tuning of the antenna to operate efficiently across the range of 2 - 30 MHz
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What is the fixed process of tuning and matching withing the HF system?
HOME, STANDBY, TUNE, OPERATE
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What position are the antenna tuning elements driven to when in HOME?
2 MHz
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What are the two types of HF antenna?
Rod and Slot
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If a rod antenna is used, what must it be equipped with?
Lightning arrester
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What size are rod antennas?
1/4 wavelength
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What is the purpose of the SELCAL system?
Relieving the pilot's workload
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What is SELCAL 32?
A new SELCAL proposal to use an additional 16 audio tones in addition to the existing 16.
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What is the use of the reset button on the Audio Control Panel?
Visual and acoustic signals can be cancelled
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What does a Cockpit Voice Recorder (CVR) do?
Record incoming/outgoing radio communications and cockpit crew voice communications
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How long should a CVR record for on an aircraft manufactured after 1st January 2021 with a maximum take-off mass of over 27000kg?
25 hours
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What frequency does the ULB transmit at?
37.5 kHz
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What should the steel casing of the CVR protect against?
Mechanical damage over up to 1000G and magnetic fields
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What temperature must a CVR withstand?
1100°C for 30 minutes
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How long does signal 5 and 6 record standard quality signals for?
120 minutes
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What is recorded on CVR channel 4?
Cockpit area microphone
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What is recorded on CVR channel 1-3?
Audio Management Unit - audio transmitted and received by the flight crew in their headphones
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What tone is audible when doing a test on the ground with the parking brake set on a Solid State Cockpit Voice Recorder (SSCVR)?
600 Hz
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When does CVR recording start automatically?
When one engine is started or the aircraft is in flight
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When does CVR recording stop?
5 minutes after the shutdown of the last engine on the ground
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What does the CVR erase function do?
Allows the crew to erase the complete recording when the aircraft is on the ground and the parking brake is set
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How long after the erase button is pressed, held down and released is the complete recording erased?
7 seconds
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What is the ACARS Data link?
Air/Ground communication network that enables the aircraft to function as a mobile terminal to transmit/recieve automatically or manually generated reports or messages to/from a ground station.
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How is operating software/customer databases loaded onto the ACARS managment unit?
Via a portable data loader direct on the front face of the ACARS MU
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What units are used to control the ACARS MU?
MCDUs, printer and the 3 Radio Management Panels (RMP)
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When VHF 3 is automatically tuned by the ACARS MU, what is displayed in the active window of the Radio Management Panels (RMP)?
ACARS
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When VHF 3 is manually tuned by a Radio Management Panel (RMP), what is displayed in the active window of RMP?
Frequency
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In order for ACARS MU to operate correctly, what is required?
Operating software, Customer database and A/C reg.
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What are the three segments of the SATCOM system?
Satellite, Aircraft Earth Stations (AES) and Ground Earth Stations (GES)
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What is the SATCOM lock-on procedure?
The procedure in which the satellite selects the available satellites, LOCKON requests sent to satellites and then sent to GES, confirmation is sent back. If reception is poor, the system will select a different satellite from the preference list.
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Other cards in this set
Card 2
Front
How is the frequency of alternating current calculated?
Back
1/T
Card 3
Front
What is the elapsed time of one period of a wave known as?
Back
Card 4
Front
How is the wavelength (λ) calculated?
Back
Card 5
Front
What is obtained when superimposing the 1st, 3rd and 5th harmonic?
Back
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