B-008
Subelement B-008
Section B-008-003
Section B-008-003
What term describes the undesired creation of new frequency components when one or more signals enter a non-linear device?
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Phase distortion
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Aliasing
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Correct AnswerIntermodulation
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Linear distortion
Intermodulation is the undesired mixing of two or more signals that creates new signals (products) at frequencies other than the original signals. The mixing may happen in the affected equipment or elsewhere around it.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
If someone tells you that signals from your hand-held transceiver are interfering with other signals on a frequency near yours, what could be the cause?
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Your hand-held has a chirp due to low battery voltage
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Your hand-held offset is wrong
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You need to reduce your output power
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Correct AnswerYour hand-held is transmitting spurious emissions
'Spurious emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'harmonics', energy at integer multiples of the operating frequency. 'Parasitic oscillation', an unwanted oscillation above or below the operating frequency. Proper adjustment and shielding prevent this whole class of transmitter problems called 'Spurious emissions'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
If your transmitter sends signals outside the band where it is transmitting, what is this called?
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Side tones
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Off-frequency emissions
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Correct AnswerSpurious emissions
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Transmitter chirping
In a band other than the one you are using. Do not confuse with "out-of-band" emissions as defined in regulations (immediately outside the necessary bandwidth). 'Spurious emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'harmonics', energy at integer multiples of the operating frequency. 'Parasitic oscillation', an unwanted oscillation above or below the operating frequency. Proper adjustment and shielding prevent this whole class of transmitter problems called 'Spurious emissions'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What problem may occur if your transmitter is operated without its cover or other shielding in place?
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Correct AnswerIt may radiate spurious emissions
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It may transmit a weak signal
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It may draw excessive current
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It may transmit a chirpy signal
'Spurious emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'harmonics', energy at integer multiples of the operating frequency. 'Parasitic oscillation', an unwanted oscillation above or below the operating frequency. Proper adjustment and shielding prevent this whole class of transmitter problems called 'Spurious emissions'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
In Morse code transmission, local RF interference (key clicks) is produced by:
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high frequency parasitic oscillations
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frequency shifting caused by poor voltage regulation
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poor wave-shaping caused by a defective filter capacitor
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Correct Answerthe making and breaking of the circuit at the Morse key
Key word: LOCAL. 'Key-Clicks' in a CW Transmitter have two manifestations. One in DISTANT receivers, caused by "too sharp rise and decay times of the carrier", results in clicks being heard several kHz away from your operating frequency. The other in NEARBY broadcast receivers, caused by the "making and breaking of the circuit at the Morse key" (sparks), results in clicks being heard just like from other electrical devices where currents are switched. The first line of defence is a 'key-click filter' in the keying circuitry, but troubleshooting in later stages may be required in a modern transmitter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Key clicks, heard from a Morse code transmitter at a distant receiver, are the result of:
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sparks emitting RF from the key contacts
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Correct Answertoo sharp rise and decay times of the keyed carrier
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power supply hum modulating the carrier
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changes in oscillator frequency on keying
Key word: DISTANT. 'Key-Clicks' in a CW Transmitter have two manifestations. One in DISTANT receivers, caused by "too sharp rise and decay times of the carrier", results in clicks being heard several kHz away from your operating frequency. The other in NEARBY broadcast receivers, caused by the "making and breaking of the circuit at the Morse key" (sparks), results in clicks being heard just like from other electrical devices where currents are switched. The first line of defence is a 'key-click filter' in the keying circuitry, but troubleshooting in later stages may be required in a modern transmitter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
In a Morse code transmission, broad bandwidth RF interference (key clicks) heard at a distance is produced by:
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mechanical instability in the oscillator
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sparking at the key contacts
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Correct Answerpoor shaping of the waveform
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frequency shifting during keying
Key word: DISTANCE. 'Key-Clicks' in a CW Transmitter have two manifestations. One in DISTANT receivers, caused by "too sharp rise and decay times of the carrier", results in clicks being heard several kHz away from your operating frequency. The other in NEARBY broadcast receivers, caused by the "making and breaking of the circuit at the Morse key" (sparks), results in clicks being heard just like from other electrical devices where currents are switched. The first line of defence is a 'key-click filter' in the keying circuitry, but troubleshooting in later stages may be required in a modern transmitter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What should you do if you learn your transmitter is producing key clicks?
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Correct AnswerCheck the keying filter and the functioning of later stages
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Use a choke in the RF power output
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Regulate the oscillator supply voltage
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Adjust your key
'Key-Clicks' in a CW Transmitter have two manifestations. One in DISTANT receivers, caused by "too sharp rise and decay times of the carrier", results in clicks being heard several kHz away from your operating frequency. The other in NEARBY broadcast receivers, caused by the "making and breaking of the circuit at the Morse key" (sparks), results in clicks being heard just like from other electrical devices where currents are switched. The first line of defence is a 'key-click filter' in the keying circuitry, but troubleshooting in later stages may be required in a modern transmitter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What term describes an unwanted oscillation in an amplifier or oscillator circuit?
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Secondary emission
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Harmonic emission
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Correct AnswerParasitic oscillation
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Frequency instability
'Spurious emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'harmonics', energy at integer multiples of the operating frequency. 'Parasitic oscillation', an unwanted oscillation above or below the operating frequency. Proper adjustment and shielding prevent this whole class of transmitter problems called 'Spurious emissions'.
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 cause parasitic oscillations in a stage?
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Unwanted negative feedback
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Oscillator drift
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Power supply instability
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Correct AnswerUnwanted positive feedback
In a circuit with gain, such as an amplifier, unexpected positive feedback from the output to the input of the circuit can launch an oscillation at some unexpected frequency.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Transmitter RF amplifiers can generate parasitic oscillations:
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Correct Answerabove or below the transmitter frequency
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on the transmitter fundamental frequency
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on VHF frequencies only
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on harmonics of the transmitter frequency
'Spurious emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'harmonics', energy at integer multiples of the operating frequency. 'Parasitic oscillation', an unwanted oscillation above or below the operating frequency. Proper adjustment and shielding prevent this whole class of transmitter problems called 'Spurious emissions'.
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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