B-003
Subelement B-003
Section B-003-010
Section B-003-010
Which series of emission modes listed below is in order from the narrowest bandwidth to the widest bandwidth?
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CW, FM voice and SSB voice
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FM voice, SSB voice and CW
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SSB voice, CW and FM voice
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Correct AnswerCW, SSB voice and FM voice
The figure in a receiver's specifications which indicates its sensitivity is the:
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audio output in watts
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number of RF amplifiers
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Correct AnswerRF input signal needed to achieve a given signal-to-noise ratio
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bandwidth of the IF in kilohertz
A measurement of the 'Signal to Noise' ratio shows how well an incoming signal overcomes the inherent internal noise of a receiver. A sensitive receiver will render more signal and little remaining noise (less background noise on the reproduced signal) when compared to the base noise in the receiver. Measuring how strong a signal is required to produce a given 'S/N' ratio permits comparing receiver sensitivities.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What are the two signal parameters presented to the user on the waterfall display (spectrogram) of a modern receiver?
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Frequency and phase
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Correct AnswerAmplitude and frequency
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Bandwidth and digital mode
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Phase and bandwidth
What is the function of automatic gain control (AGC) in a receiver?
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Maximize overall gain for greater sensitivity
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Correct AnswerLimit the change in volume due to large signal strength variations
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Remove high-amplitude short-duration noise pulses
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Improve the signal-to-distortion ratio of the detector
The primary purpose of the AGC is to constrain sound volume as weak signals and very strong signals appeared in the passband. [The secondary function is to ensure each stage is fed signals at an appropriate level for optimum operation.]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
For which of the following emission modes is it important for the receiver to be tuned accurately (within 100 Hz)?
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AM
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CW
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FM
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Correct AnswerSSB
In SSB, the FREQUENCY of the original modulating signal is conveyed by the POSITION of each side frequency within the sideband in relation to the phantom carrier (it has been suppressed). A sideband (a group of ever-changing side frequencies) is formed by the sum (Upper Sideband) or difference (Lower Sideband) of the modulating frequencies and the carrier frequency. The original frequency can only be reproduced correctly by "reinserting" a reference signal, the Beat Frequency Oscillator, at the right frequency and mixing it with the received signal. 'Beat' is a synonym of mixing.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
A superheterodyne receiver has an intermediate frequency (IF) of 455 kHz. The local oscillator runs above the operating frequency. To which frequency should it be tuned to receive a signal on 3.54 MHz?
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4.450 MHz
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13.540 MHz
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Correct Answer3.995 MHz
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4.905 MHz
The mixer accepts two inputs: the incoming signal and the local oscillator. Mixing returns two new products: the sum of the two inputs and the difference of the two inputs. The IF Filter seeks to let only one of the products into the intermediate frequency chain for amplification through the IF Amplifier. In this example, 3995 kHz minus 3540 kHz yields 455 kHz.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
When receiving a modulated signal, what is the adverse consequence of too narrow a receiver bandwidth?
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Lower signal-to-noise ratio
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Loss of dynamic range
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Correct AnswerLoss of information
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Lower signal strength
At the transmitter, the message to be conveyed and the emission mode determine the occupied bandwidth of the radio signal. The bandwidth of the receiver must be similar, otherwise part of the message is not reproduced. In fact, this bandwidth cannot be too narrow or too wide so that a compromise is struck between fidelity and superfluous noise.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Apart from sensitivity and selectivity, which of these is the third main indicator of communications receiver performance?
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Frequency range
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Fidelity
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Correct AnswerDynamic range
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Volume range
Dynamic range defines the behaviour of a receiver when faced with very strong signals. Stability was previously the third criterion, but microprocessor control (based on a crystal clock) naturally ensures adequate stability.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
A communications receiver has four filters installed in it, respectively designated as 250 Hz, 500 Hz, 2.4 kHz, and 6 kHz. If you were listening to single sideband, which filter would you utilize?
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6 kHz
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250 Hz
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500 Hz
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Correct Answer2.4 kHz
In order of bandwidth requirements: CW = about 100 Hz, RTTY = about 600 Hz, AM = 6 kHz, SSB = 2 to 3 kHz, FM = 10 to 20 kHz. A 2.4 kHz filter is just wide enough to accept an SSB signal. Wider a filter, lets in more noise. Too narrow a filter causes distortion.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
A communications receiver has four filters installed in it, respectively designated as 250 Hz, 500 Hz, 2.4 kHz and 6 kHz. You are copying a CW transmission and there is a great deal of interference. Which one of the filters would you choose?
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Correct Answer250 Hz
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6 kHz
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500 Hz
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2.4 kHz
In order of bandwidth requirements: CW = about 100 Hz, RTTY = about 600 Hz, AM = 6 kHz, SSB = 2 to 3 kHz, FM = 10 to 20 kHz. A 250 Hz filter is best to isolate a CW signal. Wider a filter, lets in more noise. Too narrow a filter causes distortion.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
When receiving CW, which of these frequency ranges is optimum for a band-pass filter?
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100 Hz to 1100 Hz
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300 Hz to 2700 Hz
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2100 Hz to 2300 Hz
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Correct Answer750 Hz to 850 Hz
After the 'product detector', an incoming CW signal is now an audible tone. Most receivers render CW as a note somewhere in the range of 750 Hz to 850 Hz. Additional band-pass filtering (allowing only a certain range of frequencies) can be useful for knocking down adjacent stations finding their way into the receiver passband (the range of frequencies allowed through the intermediate frequency chain) and producing higher or lower notes, say at 250 or 1000 Hz.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
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