B-008
Subelement B-008
Section B-008-004
Section B-008-004
If a neighbour reports television interference on one or two channels only when you transmit on 15 metres, what is probably the cause of the interference?
-
Correct AnswerHarmonic emissions from your transmitter
-
Splatter due to overmodulation
-
Television receiver front-end overload
-
Parasitic oscillations from your transmitter
Unlike 'Overload' where a TV receiver is likely to be affected by a broad range of transmitter frequencies, interference to a single TV channel from a specific band of transmitter frequencies suggests 'Harmonics' are at play. 'Harmonic Radiation' entails integer (whole number) multiples of the operating frequency. Apart from proper adjustment of the transmitter, a 'low-pass' filter with a cut-off frequency of 30 MHz helps curb harmonics out of an HF transmitter. Three times 21 MHz (15 m) affects TV channel 3 [60-66 MHz]. Four times 21 MHz affects channel 6 [82-88 MHz].
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 harmonic emissions?
-
Unwanted signals that are combined with a 60 Hz hum
-
Correct AnswerUnwanted signals at frequencies which are multiples of the fundamental (operating) frequency
-
Unwanted signals caused by mixing with a nearby transmitter
-
Signals which cause skip propagation to occur
'Harmonic Radiation' entails integer (whole number) multiples of the operating frequency. Harmonics result in signals outside the band where you operate: you may be heard on another harmonically related band (e.g., 3 times 7 MHz (40 m) = 21 MHz (15 m) ) or interfere with other services. Apart from proper adjustment of the transmitter, a 'low-pass' filter with a cut-off frequency of 30 MHz helps curb harmonics out of an HF transmitter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Why are harmonic emissions from an amateur radio station not wanted?
-
They may result in excessive power dissipation
-
They may overload a nearby transmitter
-
Correct AnswerThey may cause interference to other stations
-
They may interfere with stations on adjacent frequencies
'Harmonic Radiation' entails integer (whole number) multiples of the operating frequency. Harmonics result in signals outside the band where you operate: you may be heard on another harmonically related band (e.g., 3 times 7 MHz (40 m) = 21 MHz (15 m) ) or interfere with other services. Apart from proper adjustment of the transmitter, a 'low-pass' filter with a cut-off frequency of 30 MHz helps curb harmonics out of an HF 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 unwanted radio energy transmitted just outside the necessary bandwidth?
-
Harmonic emissions
-
Parasitic emissions
-
Spurious emissions
-
Correct Answer"Out-of-band" emissions
Key words: JUST OUTSIDE THE NECESSARY BANDWIDTH. "Out-of-band emissions: Emissions on a frequency or frequencies immediately outside the necessary bandwidth, which result from the modulation process, but exclude spurious emissions." [RSS-Gen, General Requirements for Compliance of Radio Apparatus]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
If you are told your station was heard on 21.375 MHz but at the time you were operating on 7.125 MHz. What is one reason that could cause this to happen?
-
Correct AnswerYour transmitter radiates harmonic signals
-
You were sending CW too fast
-
Your transmitter's power-supply filter choke is defective
-
Your transmitter's power-supply filter capacitor is defective
'Harmonic Radiation' entails integer (whole number) multiples of the operating frequency. Harmonics result in signals outside the band where you operate: you may be heard on another harmonically related band (e.g., 3 times 7 MHz (40 m) = 21 MHz (15 m) ) or interfere with other services. Apart from proper adjustment of the transmitter, a 'low-pass' filter with a cut-off frequency of 30 MHz helps curb harmonics out of an HF 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 causes splatter interference?
-
Correct AnswerOvermodulating a transmitter
-
Unwanted feedback in an amplifier stage
-
Keying a transmitter too fast
-
The transmitting antenna is non-resonant
'Splatter': "unwanted emission immediately outside the normal necessary bandwidth", in other words, you interfere with other stations on adjacent frequencies. Too much microphone gain or too much speech processing may lead to 'Overmodulation', a major cause of 'Splatter'. Overmodulation can also force the Linear Power Amplifier into a non-linear zone of operation, which leads to 'Harmonic Radiation'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
A television tuned to channel 3 (60 MHz - 66 MHz) experiences interference when you are transmitting on the 15-metre band. Other channels are not affected. What is the most likely cause?
-
Front-end overload of the TV
-
No high-pass filter on the TV
-
Correct AnswerHarmonic emission from your transmitter
-
No high-pass filter at your transmitter
'Harmonic Radiation' (integer multiples of the operating frequency). Harmonics of several amateur HF frequencies fall right on TV channels: Three times 21 MHz (15 m) affects TV channel 3 [60-66 MHz]. Four times 21 MHz affects channel 6 [82-88 MHz]. Twice 28 MHz (10 m) affects channel 2 [54-60 MHz].
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 probable cause of "flat topping" (non-linear operation) of an amplifier in an SSB transmitter?
-
Correct AnswerExcessive microphone gain
-
Defective sideband filter
-
Insufficient power supply current capacity
-
Defective low-pass filter
'Splatter': "unwanted emission immediately outside the normal necessary bandwidth", in other words, you interfere with other stations on adjacent frequencies. Too much microphone gain or too much speech processing may lead to 'Overmodulation', a major cause of 'Splatter'. Overmodulation can also force the Linear Power Amplifier into a non-linear zone of operation, which leads to 'Harmonic Radiation'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Which of the following may cause excessive harmonics in a transmitter?
-
Use of a non-resonant antenna
-
Correct AnswerOverdriven stages
-
Internal antenna tuner malfunction
-
Defective driver circuit
'Splatter': "unwanted emission immediately outside the normal necessary bandwidth", in other words, you interfere with other stations on adjacent frequencies. Too much microphone gain or too much speech processing may lead to 'Overmodulation', a major cause of 'Splatter'. Overmodulation can also force the Linear Power Amplifier into a non-linear zone of operation, which leads to 'Harmonic Radiation'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
An interfering signal from an HF transmitter is found to have a frequency of 56 MHz. What could be the source?
-
Third harmonic of a 15-metre transmission
-
Crystal oscillator operating on its fundamental
-
Correct AnswerSecond harmonic of a 10-metre transmission
-
Seventh harmonic of an 80-metre transmission
Key word: 56 MHz. That frequency is not allocated to the amateur radio service. 'Harmonic Radiation' (integer multiples of the operating frequency). Harmonics of several amateur HF frequencies fall right on TV channels: Three times 21 MHz (15 m) affects TV channel 3 [60-66 MHz]. Four times 21 MHz affects channel 6 [82-88 MHz]. Twice 28 MHz (10 m) affects channel 2 [54-60 MHz].
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Harmonics may be produced in the RF power amplifier of a transmitter if:
-
the oscillator frequency is unstable
-
modulation is applied to a high-level stage
-
the output tank circuit is tuned to the fundamental frequency
-
Correct Answerexcessive drive signal is applied to it
'Splatter': "unwanted emission immediately outside the normal necessary bandwidth", in other words, you interfere with other stations on adjacent frequencies. Too much microphone gain or too much speech processing may lead to 'Overmodulation', a major cause of 'Splatter'. Overmodulation can also force the Linear Power Amplifier into a non-linear zone of operation, which leads to 'Harmonic Radiation'.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
HamStudy.org™ is copyright 2025 Signal Stuff™, All rights
reserved.
View Privacy Policy | Get help with HamStudy.org™
View Privacy Policy | Get help with HamStudy.org™