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Subelement G4
Amateur Radio Practices
Section G4A
Station operation and setup
What is the purpose of the "notch filter" found on many HF transceivers?
  • To restrict the transmitter voice bandwidth
  • Correct Answer
    To reduce interference from carriers in the receiver passband
  • To eliminate receiver interference from impulse noise sources
  • To enhance the reception of a specific frequency on a crowded band

(B). The "notch filter" found on many HF transceivers is to reduce interference from carriers in the receiver passband. The "notch" refers to a narrow area of frequency interference that you want to get rid of, while being able to maintain the quality of the nearby signal you want to keep.

For more info see Wikipedia: notch filter

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What is one advantage of selecting the opposite, or "reverse," sideband when receiving CW signals on a typical HF transceiver?
  • Interference from impulse noise will be eliminated
  • More stations can be accommodated within a given signal passband
  • Correct Answer
    It may be possible to reduce or eliminate interference from other signals
  • Accidental out-of-band operation can be prevented

(C). When working with CW signals on a typical HF transceiver it may be beneficial to select the opposite or "reverse" sideband, as this may make it possible to reduce or eliminate interference from other signals. This method will work with CW, because it transmits just tones of dots and dashes. It won't work with a voice/phone signal because it would flip the speech pattern, making it impossible to understand.

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What is normally meant by operating a transceiver in "split" mode?
  • The radio is operating at half power
  • The transceiver is operating from an external power source
  • Correct Answer
    The transceiver is set to different transmit and receive frequencies
  • The transmitter is emitting an SSB signal, as opposed to DSB operation

(C). A transceiver set to different transmit and receive frequencies is said to be operating in "split" mode.


Repeaters usually use this method of operation to reduce the confusion caused by many stations operating on one frequency, all trying to transmit and hear at the same time. This allows callers to transmit and receive in an organized manner.

By using this method, a repeater can also use a number of different receive sites around a region and re-transmit the signals to a central transmitter on a nearby frequency for sending that signal back out to all listeners.

Split mode is also sometimes called Duplex mode on some transceivers.

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What reading on the plate current meter of a vacuum tube RF power amplifier indicates correct adjustment of the plate tuning control?
  • A pronounced peak
  • Correct Answer
    A pronounced dip
  • No change will be observed
  • A slow, rhythmic oscillation

(B). A pronounced dip or drop in the reading on the plate current meter of a vacuum tube RF amplifier shows that you have correct adjustment of the plate tuning control. This dip happens when the impedance is matched at the right frequency.

Note: It is kind of like "zero beating" a CW signal, with the reading/mismatch being higher either side of the correct level, and reaching zero when frequencies are matched to each other.

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What is a reason to use Automatic Level Control (ALC) with an RF power amplifier?
  • To balance the transmitter audio frequency response
  • To reduce harmonic radiation
  • Correct Answer
    To reduce distortion due to excessive drive
  • To increase overall efficiency

The ALC avoids feeding too much power to the amplifier. Too much power can cause the amplifier to overdrive, which causes distortion in the signal and extraneous interferences.

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What type of device is often used to match transmitter output impedance to an impedance not equal to 50 ohms?
  • Balanced modulator
  • SWR bridge
  • Correct Answer
    Antenna coupler or antenna tuner
  • Q multiplier

(C). For maximum power transfer it is important to match the impedance of your antenna with that of the transmitter output. Most commercially available antenna systems are set up so that the impedance matches with the 50 or 75 ohm coaxial cables used for connection. If you need to use an impedance other than 50 ohms, you will want to use an LC circuit (L stands for an Inductor, C stands for a capacitor) such as an antenna coupler to match the impedance levels between the transmitter output and antenna system.

For more info see Wikipedia, LC Circuit, Antennas-Impedance Matching

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What condition can lead to permanent damage to a solid-state RF power amplifier?
  • Insufficient drive power
  • Low input SWR
  • Shorting the input signal to ground
  • Correct Answer
    Excessive drive power

(D). Excessive drive power can lead to permanent damage when using a solid-state RF power amplifier. Pushing too much voltage through sensitive transistors can overload the circuits, causing components to be damaged or burned out. This is why it is important to use circuits such as the ALC, automatic level control, to detect excessive drive power and control it.

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What is the correct adjustment for the load or coupling control of a vacuum tube RF power amplifier?
  • Minimum SWR on the antenna
  • Minimum plate current without exceeding maximum allowable grid current
  • Highest plate voltage while minimizing grid current
  • Correct Answer
    Maximum power output without exceeding maximum allowable plate current

(D). The load or coupling control of a vacuum tube RF power amplifier should be adjusted so that it is at the maximum power output usable without exceeding the maximum allowable plate current. The Load control for the RF power amplifier should be adjusted alternately with the Tune control adjusting the plate current until the highest matching amplifier power output level can be found without overloading the plate current.

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Why is a time delay sometimes included in a transmitter keying circuit?
  • To prevent stations from interfering with one another
  • To allow the transmitter power regulators to charge properly
  • Correct Answer
    To allow time for transmit-receive changeover operations to complete properly before RF output is allowed
  • To allow time for a warning signal to be sent to other stations

The delay allows circuits to "cool down" or get rid of excess energy between transmit and receive operations, so that the system is not overdriven and components are not damaged by too much energy through the circuits.

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What is the purpose of an electronic keyer?
  • Automatic transmit/receive switching
  • Correct Answer
    Automatic generation of strings of dots and dashes for CW operation
  • VOX operation
  • Computer interface for PSK and RTTY operation

(B). An electronic keyer makes CW communications easier in that it automatically generates the strings of dots and dashes for CW operation. This type of keyer produces a wonderfully consistant signal, as the dots, dashes and spaces all are produced with the correct length and timing.

For more info see Wikipedia: Telegraph key

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Which of the following is a use for the IF shift control on a receiver?
  • Correct Answer
    To avoid interference from stations very close to the receive frequency
  • To change frequency rapidly
  • To permit listening on a different frequency from that on which you are transmitting
  • To tune in stations that are slightly off frequency without changing your transmit frequency

An intermediate frequency (IF) shift control on a receiver is a passband filter system which is used to avoid interference from stations very close to the receive frequency. This type of system uses upper and lower filters (High Pass and Low Pass) to remove the adjacent signals while allowing the desired, intermediate signal to PASS through.

Just remember: IF = InterFerence or InterFerence Filtering Is Fun

For more info see Wikipedia: Passband Filters

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Which of the following is a common use for the dual-VFO feature on a transceiver?
  • To allow transmitting on two frequencies at once
  • To permit full duplex operation - that is, transmitting and receiving at the same time
  • Correct Answer
    To permit monitoring of two different frequencies
  • To facilitate computer interface

(C). The dual VFO (Variable Frequency Oscillator) feature on a transceiver is commonly used to permit ease of monitoring the transmit and receive frequencies when they are not the same. This "split" mode uses one frequency for transmitting and another (usually on an adjacent frequency) for receiving. This way multiple users can listen and send transmissions in a more effective manner. Repeaters usually use this type of operation for ease of coordinating transmissions and reception.

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What is one reason to use the attenuator function that is present on many HF transceivers?
  • Correct Answer
    To reduce signal overload due to strong incoming signals
  • To reduce the transmitter power when driving a linear amplifier
  • To reduce power consumption when operating from batteries
  • To slow down received CW signals for better copy

(A). Attenuators are used in HF transceivers to reduce signal overload due to strong incoming signals. An attenuator acts as the opposite of an amplifier. Its purpose is to reduce the power or amplitude of a signal rather than increasing it, while still keeping the signal strong. This keeps the signal from having the distortion that would be experienced with too much incoming signal energy. Think of the attenuator as a downward volume control for the signal power.

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What is likely to happen if a transceiver's ALC system is not set properly when transmitting AFSK signals with the radio using single sideband mode?
  • ALC will invert the modulation of the AFSK mode
  • Correct Answer
    Improper action of ALC distorts the signal and can cause spurious emissions
  • When using digital modes, too much ALC activity can cause the transmitter to overheat
  • All these choices are correct

(B) Improper action of ALC distorts the signal and can cause spurious emissions


The Automatic Level Control (ALC) makes sure signals do not clip by compressing them. If you've dealt with audio production, this is a similar process to dynamic compression. The compressed signal has sounds similar to the original signal, but it usually comes with distortion.

This distortion is acceptable in voice communication, but in digital modes, compression may generate emissions not intended by the pure signal from your computer.

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Which of the following can be a symptom of transmitted RF being picked up by an audio cable carrying AFSK data signals between a computer and a transceiver?
  • The VOX circuit does not un-key the transmitter
  • The transmitter signal is distorted
  • Frequent connection timeouts
  • Correct Answer
    All these choices are correct

RF interference on an audio cable can compromise the audio quality between the two devices, resulting in any number of issues when attempting to use the signal.

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How does a noise blanker work?
  • By temporarily increasing received bandwidth
  • By redirecting noise pulses into a filter capacitor
  • Correct Answer
    By reducing receiver gain during a noise pulse
  • By clipping noise peaks

The noise blanker works on eliminating the annoying sound of repetitive pulses such that are heard with automotive ignition energy, some diesel engines, or the famous Russian 'Woodpecker' radar radio frequency emissions.

https://en.wikipedia.org/wiki/Noise_blanker

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What happens as the noise reduction control level in a receiver is increased?
  • Correct Answer
    Received signals may become distorted
  • Received frequency may become unstable
  • CW signals may become severely attenuated
  • Received frequency may shift several kHz

As the noise reduction control is made to be more agressive, additional parts of the signal become progressively targeted. Some of these parts are valuable to the quality of the audio.

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