B-003
Subelement B-003
Section B-003-011
Section B-003-011
What does chirp mean?
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Correct AnswerA small change in the output frequency of a transmitter each time a dit or dah is sent
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A slow change in transmitter frequency as the oscillator warms up
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An overload in a receiver's audio circuit whenever CW is received
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A high-pitched tone which is received along with every CW dit and dah
"Chirp": Inadequate voltage regulation causes the oscillator's frequency to shift when the telegraph key is pressed. Perceived at the receive location as a change of pitch during each Morse element.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What can be done to keep a CW transmitter from chirping?
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Correct AnswerKeep the power supply voltages very steady under varying loads
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Add a key click filter
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Add a low-pass filter
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Keep the oscillator impedance very steady under the transmit load
"Chirp": Inadequate voltage regulation causes the oscillator's frequency to shift when the telegraph key is pressed. Perceived at the receive location as a change of pitch during each Morse element. Current varies, as demand varies in a transmitter. A low-pass filter reduces 'harmonics'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the advantage of using a variable frequency oscillator in a basic CW transmitter?
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Greater suppression of harmonics
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Correct AnswerFrequency is not constrained to the available crystals
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Use of higher speed Morse code is supported
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Greater suppression of key clicks
Unlike a crystal oscillator where the frequency is locked to the component, the variable frequency oscillator allows the operator to choose the operating frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Which type of transmitter modulation changes the amplitude of an RF wave for the purpose of conveying information?
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Phase modulation
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Frequency shift keying
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Correct AnswerAmplitude modulation
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Frequency modulation
Key word: AMPLITUDE. The instantaneous voltage of an AC waveform. AM (amplitude modulation) impresses the message onto the RF carrier by varying its amplitude.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
In what emission mode does the instantaneous amplitude (envelope) of the RF signal vary with the modulating audio?
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Correct AnswerAmplitude modulation
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Frequency shift keying
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Pulse modulation
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Frequency modulation
Key word: AMPLITUDE. The instantaneous voltage of an AC waveform. AM (amplitude modulation) impresses the message onto the RF carrier by varying its amplitude.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Morse code is usually transmitted by radio as:
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a continuous carrier
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Correct Answeran interrupted carrier
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a series of key clicks
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a phase-shifted carrier
Telegraphy is equivalent to 'on-off keying' (an 'interrupted carrier'). The telegraph key allows the operator to send bursts of RF energy to the antenna per the rhythm of his hand movement on the key. Key clicks are a type of interference where a CW signal generates unwanted sidebands (excessive bandwidth).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
You are transmitting using amplitude modulation. What bandwidth does your signal occupy if the highest frequency of your voice is 3 kHz?
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Correct Answer6 kHz
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9 kHz
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12 kHz
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3 kHz
An amplitude modulated radio signal carries two sidebands, one on each side of the carrier frequency. The bandwidth of a sideband is determined by the highest modulating frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What frequency components are present in the bandwidth of an amplitude modulated signal?
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Carrier and one sideband
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Correct AnswerCarrier and two sidebands
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Two sidebands
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One sideband
An amplitude modulated radio signal carries two sidebands, one on each side of the carrier frequency. The bandwidth of a sideband is determined by the highest modulating frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
An RF oscillator should be electrically and mechanically stable. This is to ensure that the oscillator does NOT:
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become overmodulated
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cause undue distortion
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Correct Answerdrift in frequency over time
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generate key clicks
Key word: STABLE. Absence of frequency "drift". A good oscillator remains on frequency despite mechanical vibrations, voltage or temperature variations.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
The DC power to the final stage of your transmitter is 200 watts and the RF output is 125 watts. What has happened to the rest of the power?
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It has been used to provide negative feedback
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Correct AnswerIt has been dissipated as heat
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It has been used to provide positive feedback
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It has been used to provide greater efficiency
Power Amplifiers have a certain 'efficiency', the ratio of DC power required to obtain an RF output. The difference goes up in heat. This is the reason for the 'heat sinks' on the back of transmitters.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
The difference between DC input power and RF output power of a transmitter RF amplifier:
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is lost in the transmission line
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Correct Answerappears as heat
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is due to oscillations
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radiates from the antenna
Power Amplifiers have a certain 'efficiency', the ratio of DC power required to obtain an RF output. The difference goes up in heat. This is the reason for the 'heat sinks' on the back of transmitters.
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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