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.

General hint for most questions like this one: “WE HATE INTERFERENCE”

For more info see Wikipedia: notch filter

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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.

HINT: "REverse" in the question; "REduce" in the correct answer.

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(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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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 on either side of the correct level, and reaching zero when frequencies are matched to each other.

Mnemonics:

• To "peak the grid, dip the plate".
• Keep tuning until you stop wasting electricity (low current).

What is plate current?

Plate Current is the amperage that flows across a tube from the cathode to the plate. In the case of an audio tube, the control grid and screen grid mediate the amount of current that flows from cathode to plate.

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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.

hint: Vehicle Automatic Traction Control helps to "Prevent excessive drive"

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(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 the 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 the antenna system.

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

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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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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.

HINT: both the question and answer use the word "power"

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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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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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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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(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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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.

Memory device: Receive attenuator prevents receiver overload.

Attenuation means to reduce; overload means to overburden or strain. When a signal is too strong you can attenuate the signal to prevent overloading the receiver.

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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 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.

Hint: Wrong Action Distorts

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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.

Hint: If two of them are right, then the answer is All these choices are correct.

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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

Noise Blanket "Blanker" works to reduce cold "Receiver gain" during a cold front "Noise pulse"

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

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