Login or Register for FREE!
Login or Register for FREE!
Subel. L13
55 questions
Subelement L13

Interference and Suppression.

Section L13

What is meant by receiver overload?

  • Correct Answer
    Interference caused by strong signals from a nearby transmitter
  • Interference caused by turning the volume up too high
  • Too much current from the power supply
  • Too much voltage from the power supply

'Receiver Overload', also known as 'Front-End Overload' or 'RF Overload', is a problem where the early stages of a receiver (i.e., RF amplifier or Mixer) are overwhelmed by some strong nearby transmitter. For example, TV reception is affected by an HF transmitter. In the case of 'Overload', the exact transmit frequency does not seem to matter: the effect is the same for a broad range of transmit frequencies. This contrasts with 'Harmonics' where a multiple of a given transmit frequency is the cause of the interference.

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 one way to tell if radio frequency interference to a receiver is caused by front-end overload?

  • If connecting a low pass filter to the transmitter greatly cuts down the interference
  • Correct Answer
    If the interference is about the same no matter what frequency is used for the transmitter
  • If grounding the receiver makes the problem worse
  • If connecting a low pass filter to the receiver greatly cuts down the interference

'Receiver Overload', also known as 'Front-End Overload' or 'RF Overload', is a problem where the early stages of a receiver (i.e., RF amplifier or Mixer) are overwhelmed by some strong nearby transmitter. For example, TV reception is affected by an HF transmitter. In the case of 'Overload', the exact transmit frequency does not seem to matter: the effect is the same for a broad range of transmit frequencies. This contrasts with 'Harmonics' where a multiple of a given transmit frequency is the cause of the interference.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

If a neighbour reports television interference whenever you transmit, no matter what band you use, what is probably the cause of the interference?

  • Correct Answer
    Receiver overload
  • Incorrect antenna length
  • Receiver VR tube discharge
  • Too little transmitter harmonic suppression

'Receiver Overload', also known as 'Front-End Overload' or 'RF Overload', is a problem where the early stages of a receiver (i.e., RF amplifier or Mixer) are overwhelmed by some strong nearby transmitter. For example, TV reception is affected by an HF transmitter. In the case of 'Overload', the exact transmit frequency does not seem to matter: the effect is the same for a broad range of transmit frequencies. This contrasts with 'Harmonics' where a multiple of a given transmit frequency is the cause of the interference.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What type of filter should be connected to a TV receiver as the first step in trying to prevent RF overload from an amateur HF station transmission?

  • Correct Answer
    High-pass
  • Low-pass
  • Band-pass
  • No filter

key words: TV, OVERLOAD, HF. TV Channels begin at 54 MHz; the HF range ends at 30 MHz. To prevent overload to a TV receiver from an HF transmitter, a HIGH-PASS filter can be installed on the TV receiver to allow higher frequencies through while attenuating lower frequencies. The object of the filtering being to keep the HF signals out of the TV receiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

During a club ARRL Field Day outing, reception on the 20 m SSB station is compromised every time the 20 m CW station is on the air. What might cause such interference?

  • Improper station grounding
  • Harmonic radiation
  • Correct Answer
    Receiver desensitization
  • Both stations are fed from the same generator

The proximity of a transmitter a short distance from a receiver, especially on the same band, may cause receiver overload. Symptoms can be loss of receiver sensitivity (desensitization) or weird noises.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Intermodulation in a broadcast receiver by a nearby transmitter would be noticed in the receiver as:

  • distortion on transmitted voice peaks
  • interference continuously across the dial
  • Correct Answer
    the undesired signal in the background of the desired signal
  • interference only when a broadcast signal is tuned

key words: IN THE BACKGROUND. In 2014, Innovation, Science and Economic Development Canada chose to replace the word "cross-modulation" with "intermodulation". 'Cross-Modulation' is a special case of overload: it too supposes a strong undesired signal. The peculiarity of 'Cross-Modulation' is that the two signals are heard at the same time: the one you want AND the undesired interfering signal.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

You have connected your hand-held VHF transceiver to an outside gain antenna. You now hear a mixture of signals together with different modulation on your desired frequency. What is the nature of this interference?

  • Audio stage intermodulation interference
  • Correct Answer
    Receiver intermodulation interference
  • Harmonic interference from other stations
  • Audio stage overload interference

"Intermod" for short, a plague in urban environments. High-powered transmitters used for commercial purposes multiply the possibilities that two or more signals mix and produce a result (product) which OVERLOADS your receiver. The actual mixing may occur in your receiver, in which case filtering might be helpful, or elsewhere altogether. The results: loss of sensitivity, noises and squeals covering the intended signal in your receiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Two or more strong out-of-band signals mix in your receiver to produce interference on a desired frequency. What is this called?

  • Front-end desensitization
  • Correct Answer
    Intermodulation interference
  • Receiver quieting
  • Capture effect

"Intermod" for short, a plague in urban environments. High-powered transmitters used for commercial purposes multiply the possibilities that two or more signals mix and produce a result (product) which OVERLOADS your receiver. The actual mixing may occur in your receiver, in which case filtering might be helpful, or elsewhere altogether. The results: loss of sensitivity, noises and squeals covering the intended signal in your receiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Two mobile stations are traveling along the same road in close proximity to each other and having trouble communicating through a local repeater. Why may it be necessary to use simplex operation to communicate between these cars?

  • Correct Answer
    The strong signal of one mobile transmitter may desensitize the receiver of the other mobile receiver
  • Simplex operation does not require the use of CTCSS tones
  • There is less time delay using simplex operation compared to using a repeater
  • There are many more simplex frequencies than repeater frequencies available

The proximity of a transmitter a short distance from a receiver, especially on the same band, may cause receiver overload. Symptoms can be loss of receiver sensitivity (desensitization) or weird noises.

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 receiver suffers interference on channel 5 (76 - 82 MHz) only when you transmit on 14 MHz. From your home you see the tower of a commercial FM station known to broadcast on 92.5 MHz. Which of these solutions would you try first?

  • Insert a low pass filter at the antenna connector of the HF transmitter
  • Insert a high pass filter at the antenna connector of the HF transmitter
  • Insert a low pass filter at the antenna connector of the television
  • Correct Answer
    Insert a high pass filter at the antenna connector of the television

'Cross-Modulation' is a special case of overload. TV Channels begin at 54 MHz; the HF range ends at 30 MHz. To prevent overload to a TV receiver from an HF transmitter, a HIGH-PASS filter can be installed on the TV receiver to allow higher frequencies through while attenuating lower frequencies. The object of the filtering being to keep the HF signals out of the TV receiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

How can intermodulation be reduced?

  • By adjusting the passband tuning
  • Correct Answer
    By installing a suitable filter at the receiver
  • By using a better antenna
  • By increasing the receiver RF gain while decreasing the AF gain

TV Channels begin at 54 MHz; the HF range ends at 30 MHz. To prevent overload to a TV receiver from an HF transmitter, a HIGH-PASS filter can be installed on the TV receiver to allow higher frequencies through while attenuating lower frequencies. The object of the filtering being to keep the HF signals out of the TV receiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What devices would you install to reduce or eliminate audio frequency interference to home entertainment systems?

  • Bypass inductors
  • Correct Answer
    Coils on ferrite cores
  • Bypass resistors
  • Metal-oxide varistors

A frequent cause of interference to home entertainment systems is that the long speaker leads act as antennas and bring radio energy into the audio amplifier stages, audio rectification ensues. Keeping the RF out of the audio circuitry can be achieved by winding the speaker leads on ferrite cores to form a choke (high inductive reactance at RF).

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 be done if a properly operating amateur station is the cause of interference to a nearby telephone?

  • Make internal adjustments to the telephone equipment
  • Correct Answer
    Install a modular plug-in telephone RFI filter close to the telephone device
  • Ground and shield the local telephone distribution amplifier
  • Stop transmitting whenever the telephone is in use

"RFI Filter" = Radio Frequency Interference filter. Much like home entertainment systems with their long speaker leads acting as antennas, wire-line telephones with cabling running through the house and streets can easily pickup RF energy. Filters installed at the telephone set usually solve the problem.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What sound is heard from a public-address system if audio rectification of a nearby single-sideband phone transmission occurs?

  • A steady hum whenever the transmitter's carrier is on the air
  • Correct Answer
    Distorted speech from the transmitter's signals
  • Clearly audible speech from the transmitter's signals
  • On-and-off humming or clicking

Much like home entertainment systems, the long speaker leads in a Public-Address sound system act as antennas and bring radio energy into the audio amplifier stages. Interfering SSB signals are heard as distorted speech in the sound system. Interfering CW signals are heard as on-and-off clicks or hum.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What sound is heard from a public-address system if audio rectification of a nearby CW transmission occurs?

  • A steady whistling
  • Correct Answer
    On-and-off humming or clicking
  • Audible, possibly distorted speech
  • Muffled, severely distorted speech

Much like home entertainment systems, the long speaker leads in a Public-Address sound system act as antennas and bring radio energy into the audio amplifier stages. Interfering SSB signals are heard as distorted speech in the sound system. Interfering CW signals are heard as on-and-off clicks or hum.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

How can you minimize the possibility of audio rectification of your transmitter's signals?

  • Use CW only
  • Use a solid-state transmitter
  • Correct Answer
    Ensure that all station equipment is properly grounded
  • Install bypass capacitors on all power supply rectifiers

Properly grounding all station equipment minimizes the radiation of RF which may couple into house wiring and affect other devices in the household.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

An amateur transmitter is being heard across the entire dial of a broadcast receiver. The receiver is most probably suffering from:

  • splatter from the transmitter
  • Correct Answer
    audio rectification in the receiver
  • harmonics interference from the transmitter
  • poor image rejection

key words: ACROSS THE DIAL. This has to be a case of OVERLOAD. 'Cross-Modulation' and 'Audio Rectification' are two manifestations of overload. All other choices would not appear 'across the dial': an 'Harmonic' falls on a precise frequency, 'Splatter' is limited to a few kilohertz.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Your SSB HF transmissions are heard muffled on a sound system in the living room regardless of its volume setting. What causes this?

  • Harmonics generated at the transmitter
  • Improper filtering in the transmitter
  • Lack of receiver sensitivity and selectivity
  • Correct Answer
    Audio rectification of strong signals

key words: STRONG SIGNAL. 'Cross-Modulation' is a special case of overload. Nothing needs to be wrong with the affected receiver or the transmitter. It is simply that the receiver is exposed to more radio energy that it can handle. 'Rectification' leads to 'detection': any semiconductor device may start acting like a diode and perform the two functions.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What device can be used to minimize the effect of RF pickup by audio wires connected to stereo speakers, intercom amplifiers, telephones, etc.?

  • Attenuator
  • Diode
  • Correct Answer
    Ferrite core
  • Magnet

Long wires act as antennas. The wires should be kept as short as possible. Winding speaker or telephone wires around a 'ferrite core' makes an Inductor (a coil). Inductors oppose (inductive reactance) high frequency AC signals such as radio frequency. The 'ferrite core' makes for more inductance even with only a few turns of wire. Ferrite is a material with electromagnetic properties.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Stereo speaker leads often act as antennas to pick up RF signals. What is one method you can use to minimize this effect?

  • Connect the speaker through an audio attenuator
  • Connect a diode across the speaker
  • Correct Answer
    Shorten the leads
  • Lengthen the leads

Long wires act as antennas. The wires should be kept as short as possible. Winding speaker or telephone wires around a 'ferrite core' makes an Inductor (a coil). Inductors oppose (inductive reactance) high frequency AC signals such as radio frequency. The 'ferrite core' makes for more inductance even with only a few turns of wire. Ferrite is a material with electromagnetic properties.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

One method of preventing RF from entering a stereo set through the speaker leads is to wrap each of the speaker leads:

  • around a wooden dowel
  • Correct Answer
    through a ferrite core
  • around a copper bar
  • around an iron bar

Long wires act as antennas. The wires should be kept as short as possible. Winding speaker or telephone wires around a 'ferrite core' makes an Inductor (a coil). Inductors oppose (inductive reactance) high frequency AC signals such as radio frequency. The 'ferrite core' makes for more inductance even with only a few turns of wire. Ferrite is a material with electromagnetic properties.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Stereo amplifiers often have long leads which pick up transmitted signals because they act as:

  • Correct Answer
    receiving antennas
  • transmitting antennas
  • RF attenuators
  • frequency discriminators

Long wires act as antennas. The wires should be kept as short as possible. Winding speaker or telephone wires around a 'ferrite core' makes an Inductor (a coil). Inductors oppose (inductive reactance) high frequency AC signals such as radio frequency. The 'ferrite core' makes for more inductance even with only a few turns of wire. Ferrite is a material with electromagnetic properties.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

How can you prevent key-clicks?

  • By using a better power supply
  • By sending CW more slowly
  • Correct Answer
    By using a key-click filter
  • By increasing power

'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

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?

  • You need to turn the volume up on your hand-held
  • Correct Answer
    Your hand-held is transmitting spurious emissions
  • You need a power amplifier for your hand-held
  • Your hand-held has a chirp from weak batteries

'Spurious Emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'Harmonics', energy at integer multiples of the operating frequency. 'Parasitic Oscillations', 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?

  • Side tones
  • Transmitter chirping
  • Off-frequency emissions
  • Correct Answer
    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 Oscillations', 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 the cover and other shielding in place?

  • It may interfere with other stations operating near its frequency
  • It may transmit a chirpy signal
  • Correct Answer
    It may radiate spurious emissions
  • It may transmit a weak 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 Oscillations', 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:

  • the power amplifier, and is caused by high frequency parasitic oscillations
  • poor waveshaping caused by a poor voltage regulator
  • Correct Answer
    the making and breaking of the circuit at the Morse key
  • frequency shifting caused by poor voltage regulation

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:

  • power supply hum modulating the carrier
  • sparks emitting RF from the key contacts
  • changes in oscillator frequency on keying
  • Correct Answer
    too sharp rise and decay times of the keyed carrier

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:

  • Correct Answer
    poor shaping of the waveform
  • shift in frequency when keying the transmitter
  • sparking at the key contacts
  • sudden movement in the receiver loudspeaker

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?

  • Correct Answer
    Check the keying filter and the functioning of later stages
  • Turn the receiver down
  • Regulate the oscillator supply voltage
  • Use a choke in the RF power output

'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

A parasitic oscillation:

  • does not cause any radio interference
  • is produced in a transmitter oscillator stage
  • Correct Answer
    is an unwanted signal developed in a transmitter
  • is generated by parasitic elements of a Yagi beam

'Spurious Emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'Harmonics', energy at integer multiples of the operating frequency. 'Parasitic Oscillations', 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

Parasitic oscillations in the RF power amplifier stage of a transmitter may be found:

  • at high frequencies only
  • at low frequencies only
  • Correct Answer
    at high or low frequencies
  • on harmonic frequencies

'Spurious Emissions': signals radiated at a frequency other than the operating frequency. Two examples: 'Harmonics', energy at integer multiples of the operating frequency. 'Parasitic Oscillations', 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

Transmitter RF amplifiers can generate parasitic oscillations:

  • on VHF frequencies only
  • on the transmitter fundamental frequency
  • on harmonics of the transmitter frequency
  • Correct Answer
    above or below 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 Oscillations', 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 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?

  • Too much low pass filtering on the transmitter
  • Correct Answer
    Harmonic radiation from your transmitter
  • De ionization of the ionosphere near your neighbour's TV antenna
  • TV receiver front-end overload

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 cutoff 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 is meant by harmonic radiation?

  • Signals which cause skip propagation to occur
  • Correct Answer
    Unwanted signals at frequencies which are multiples of the fundamental (chosen) frequency
  • Unwanted signals that are combined with a 60-Hz hum
  • Unwanted signals caused by sympathetic vibrations from a nearby transmitter

'Harmonic Radiation' entails integer (whole-number) multiples of the operating frequency. Harmonics result in 'out-of-band' signals: 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 cutoff 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 is harmonic radiation from an amateur station not wanted?

  • It may cause auroras in the air
  • Correct Answer
    It may cause interference to other stations and may result in out-of-band signals
  • It uses large amounts of electric power
  • It may cause sympathetic vibrations in nearby transmitters

'Harmonic Radiation' entails integer (whole-number) multiples of the operating frequency. Harmonics result in 'out-of-band' signals: 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 cutoff 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 type of interference may come from a multi-band antenna connected to a poorly tuned transmitter?

  • Correct Answer
    Harmonic radiation
  • Parasitic excitation
  • Intermodulation
  • Auroral distortion

key words: POORLY TUNED TX, MULTI-BAND ANTENNA. Improper adjustment of the transmitter may cause it to put out 'Harmonic Radiation' (integer multiples of the operating frequency). The multi-band antenna will readily radiate these signals at other frequencies.

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 kHz, but at the time you were operating on 7125 kHz, what is one reason this could happen?

  • You were sending CW too fast
  • Your transmitter's power-supply filter capacitor was bad
  • Correct Answer
    Your transmitter was radiating harmonic signals
  • Your transmitter's power-supply filter choke was bad

'Harmonic Radiation' entails integer (whole-number) multiples of the operating frequency. Harmonics result in 'out-of-band' signals: 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 cutoff 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?

  • Keying a transmitter too fast
  • Signals from a transmitter's output circuit are being sent back to its input circuit
  • The transmitting antenna is the wrong length
  • Correct Answer
    Overmodulating a transmitter

'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

Your amateur radio transmitter appears to be creating interference to the television on channel 3 (60-66 MHz) when you are transmitting on the 15 metre band. Other channels are not affected. The most likely cause is:

  • a bad ground at the transmitter
  • front-end overload of the TV
  • Correct Answer
    harmonic radiation from the transmitter
  • no high-pass filter on the TV

'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

One possible cause of TV interference by harmonics from an SSB transmitter is from "flat topping" - driving the power amplifier into non-linear operation. The most appropriate remedy for this is:

  • use another antenna
  • reduce oscillator output
  • Correct Answer
    reduce microphone gain
  • retune transmitter output

'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

In a transmitter, excessive harmonics are produced by:

  • Correct Answer
    overdriven stages
  • low SWR
  • resonant circuits
  • a linear amplifier

'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 a transmitter is found to have a frequency of 57 MHz (TV Channel 2 is 54 - 60 MHz). This signal could be the:

  • Correct Answer
    second harmonic of a 10 metre transmission
  • crystal oscillator operating on its fundamental
  • seventh harmonic of an 80 metre transmission
  • third harmonic of a 15 metre transmission

'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:

  • modulation is applied to a high-level stage
  • Correct Answer
    excessive drive signal is applied to it
  • the output tank circuit is tuned to the fundamental frequency
  • the oscillator frequency is unstable

'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

What type of filter might be connected to an amateur HF transmitter to cut down on harmonic radiation?

  • A high pass filter
  • A CW filter
  • Correct Answer
    A low pass filter
  • A key-click filter

key word: HARMONIC. 'Harmonic Radiation' (integer multiples of the operating frequency). A 'Low-Pass' filter with a cutoff frequency of 30 MHz helps curb harmonics out of an HF transmitter. The 'Key-Click' filter (choke/capacitor) is used at the telegraph key to prevent 'key-click' interference. A 'High-Pass' filter is used on a TV receiver to prevent overload from an HF transceiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Why do modern HF transmitters have a built-in low pass filter in their RF output circuits?

  • To reduce RF energy below a cut-off point
  • Correct Answer
    To reduce harmonic radiation
  • To reduce fundamental radiation
  • To reduce low frequency interference to other amateurs

key words: LOW-PASS. 'Harmonic Radiation' (integer multiples of the operating frequency). A 'Low-Pass' filter with a cutoff 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 circuit blocks RF energy above and below a certain limit?

  • A low pass filter
  • Correct Answer
    A band pass filter
  • A high pass filter
  • An input filter

key words: BLOCKS ABOVE AND BELOW. A 'Band-Pass' filter lets frequencies between two design limits pass unaffected. Outside of that range, attenuation is present. A 'High-Pass' filter passes frequencies above a certain limit but attenuates lower frequencies. A 'Low-Pass' filter lets frequencies below its cutoff frequency pass unimpeded but attenuates higher frequencies.

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 be the impedance of a low pass filter as compared to the impedance of the transmission line into which it is inserted?

  • Substantially higher
  • Correct Answer
    About the same
  • Substantially lower
  • Twice the transmission line impedance

All filters are designed with a given impedance in mind. The source impedance and load impedance must match the design criteria of the filter for it to function optimally.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In order to reduce the harmonic output of a high frequency (HF) transmitter, which of the following filters should be installed at the transmitter?

  • Rejection
  • Correct Answer
    Low pass
  • Key click
  • High pass

key word: HARMONIC. 'Harmonic Radiation' (integer multiples of the operating frequency). A 'Low-Pass' filter with a cutoff frequency of 30 MHz helps curb harmonics out of an HF transmitter. A 'High-Pass' filter is used on a TV receiver to prevent overload from an HF transceiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

To reduce harmonic output from a high frequency transmitter, you would put a ____________ in the transmission line as close to the transmitter as possible.

  • wave trap
  • Correct Answer
    low pass filter
  • high pass filter
  • band reject filter

key word: HARMONIC. 'Harmonic Radiation' (integer multiples of the operating frequency). A 'Low-Pass' filter with a cutoff frequency of 30 MHz helps curb harmonics out of an HF transmitter. A 'High-Pass' filter is used on a TV receiver to prevent overload from an HF transceiver.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

To reduce energy from an HF transmitter getting into a television set, you would place a ____________ as close to the TV as possible.

  • band reject filter
  • Correct Answer
    high pass filter
  • low pass filter
  • wave trap

A 'High-Pass' filter is used on a TV receiver to prevent overload from an HF transceiver. A 'Low-Pass' filter with a cutoff 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

A band pass filter will:

  • attenuate high frequencies but not low
  • pass frequencies each side of a band
  • stop frequencies in a certain band
  • Correct Answer
    allow only certain frequencies through

A 'Band-Pass' filter lets frequencies between two design limits pass unaffected. Outside of that range, attenuation is present. A 'Low-Pass' filter lets frequencies below its cutoff frequency pass unimpeded but attenuates higher frequencies. A 'Band-Reject' filter passes everything BUT a narrow range of frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A band reject filter will:

  • allow only two frequencies through
  • pass frequencies below 100 MHz
  • stop frequencies each side of a band
  • Correct Answer
    pass frequencies each side of a band

A 'Band-Reject' filter passes everything BUT a narrow range of frequencies. A 'Low-Pass' filter lets frequencies below its cutoff frequency pass unimpeded but attenuates higher frequencies. A 'Band-Pass' filter lets frequencies between two design limits pass unaffected. Outside of that range, attenuation is present.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A high pass filter would normally be fitted:

  • between transmitter output and transmission line
  • Correct Answer
    at the antenna terminals of the TV receiver
  • between microphone and speech amplifier
  • at the Morse key or keying relay in a transmitter

A 'High-Pass' filter is used on a TV receiver to prevent overload from an HF transceiver. A 'Key-Click' filter (choke/capacitor) is used at the telegraph key to prevent 'key-click' interference. A 'Low-Pass' filter with a cutoff 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

A low pass filter suitable for a high frequency transmitter would:

  • pass audio frequencies below 3 kHz
  • Correct Answer
    attenuate frequencies above 30 MHz
  • pass audio frequencies above 3 kHz
  • attenuate frequencies below 30 MHz

key words: HIGH-FREQUENCY. A 'Low-Pass' filter with a cutoff frequency of 30 MHz helps curb harmonics out of an HF transmitter. The filter allows frequencies BELOW the cutoff to pass freely but attenuates frequencies above the cutoff. The HF segment of the radio spectrum spans 3 MHz to 30 MHz.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Go to L12 Go to L14a
HamStudy.org™ is copyright 2024 Signal Stuff™, All rights reserved.
View Privacy Policy    |    Get help with HamStudy.org™