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Subelement T4
Amateur radio practices and station set-up
Section T4B
Operating controls: tuning; use of filters; squelch function; AGC; transceiver operation; memory channels
What may happen if a transmitter is operated with the microphone gain set too high?
  • The output power might be too high
  • Correct Answer
    The output signal might become distorted
  • The frequency might vary
  • The SWR might increase

Some microphones have an adjustable gain control. Some radios have an internal gain control to trim the audio gain of the microphone. If the gain is set too high it can exceed the range that circuitry can handle and will cause the audio signal to be distorted. Distortion might be fine for your old tube type guitar amplifier but it will render your signal quality as unreadable.

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Tags: troubleshooting noise and interference arrl chapter 5 arrl module 11

Which of the following can be used to enter the operating frequency on a modern transceiver?
  • Correct Answer
    The keypad or VFO knob
  • The CTCSS or DTMF encoder
  • The Automatic Frequency Control
  • All of these choices are correct

VFO means Variable Frequency Oscillator; back in the time of crystals you often had to "program" a radio by changing crystals in the radio and then using a knob to select them. Modern radios are much easier to set up; most of them you can simply type in the frequency you want on the keypad. Some lack a keypad, but have a "tuning knob", or "VFO knob". Many have both options, since each has its uses.

CTCSS refers to a subaudible tone (also called a PL tone or a privacy code by FRS manufacturers) and DTMF tones are the tones generated when you press a key on your telephone; neither has anything to do with entering the operating frequency. Automatic Frequency Control keeps the receiver tuned to an incoming signal - thus it is not a method of entering an operating frequency.

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Tags: radio operation arrl chapter 5 arrl module 11

What is the purpose of the squelch control on a transceiver?
  • To set the highest level of volume desired
  • To set the transmitter power level
  • To adjust the automatic gain control
  • Correct Answer
    To mute receiver output noise when no signal is being received

The squelch control on a transceiver will "squelch" or mute the noise when no signal is received.

The receiver portion of the transceiver is very sensitive and has variable amplification to give gain to weak signals. When there is no signal to receive, this gain is at maximum which makes the noise received as loud as a normal signal. Fortunately we do not have to listen to that noise because we can adjust the squelch control to mute or turn off signals that are not stronger than the setting we choose.

The squelch circuit watches the signal strength detector's output and turns on the signal when it is strong enough. By turning the squelch control up too high you may miss weaker stations. By turning it too low you will hear the "white noise" received continuously or intermittently as the background noise varies.

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Tags: radio operation arrl chapter 5 arrl module 11

What is a way to enable quick access to a favorite frequency on your transceiver?
  • Enable the CTCSS tones
  • Correct Answer
    Store the frequency in a memory channel
  • Disable the CTCSS tones
  • Use the scan mode to select the desired frequency

The ability of most radios to store/program and recall our favorite frequencies gives us quick access to them. These memories can be programmed with more than just the frequency that is needed. For example to reach a repeater we need the correct frequency, input offset frequency and CTCSS tone.

The distractor answers may sound right but remember the key words here are frequency, which is found in the question and correct answer, quick and memory. A good memory is important to get the right frequency recalled quickly.

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Tags: radio operation arrl chapter 5 arrl module 11

Which of the following would reduce ignition interference to a receiver?
  • Change frequency slightly
  • Decrease the squelch setting
  • Correct Answer
    Turn on the noise blanker
  • Use the RIT control

Ignition interference is interference that comes from the ignition of a vehicle engine. Newer vehicles seem to have this problem less than older ones did, but it is still not uncommon to have an engine that produces enough noise (particularly if your power or feed lines are poorly shielded) to cause your radio's squelch to open when there is no real signal or even to make it more difficult to hear a weak signal.

A noise blanker is a device that is designed to filter out some of this interference. They work in different ways, and some work better than others.

Note that with ignition interference, changing the frequency (which is what a Receiver Incremental Tuning (RIT) control would do), is not going to help; increasing the squelch setting might help you ignore the problem if the noise is slight, but decreasing it would certainly not help...

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Tags: troubleshooting radio operation noise and interference hf arrl chapter 5 arrl module 11

Which of the following controls could be used if the voice pitch of a single-sideband signal seems too high or low?
  • The AGC or limiter
  • The bandwidth selection
  • The tone squelch
  • Correct Answer
    The receiver RIT or clarifier

RIT stands for Receiver Incremental Tuning. It is a fine tuning control to adjust the receiver frequency without adjusting the transmitter frequency.

While SSB is a very efficient transmission mode, everyone ends up sounding somewhat like Donald Duck. This is due to the fact that the transmit carrier frequency is missing. RIT Stands for Receiver Incremental Tuning which in effect, recreates the signal's missing carrier transmit frequency. When the RIT adjustment is misadjusted, the result can be a voice which is too high or too low sounding. Adjust the RIT until the voice sounds correct. Keep in mind some people have naturally higher voices than others. The direction you adjust the RIT will be in opposite directions for upper sideband (USB) vs. lower sideband (LSB), SSB signals.

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Tags: radio operation hf arrl chapter 5 arrl module 11

What does the term “RIT” mean?
  • Receiver Input Tone
  • Correct Answer
    Receiver Incremental Tuning
  • Rectifier Inverter Test
  • Remote Input Transmitter

Sometimes you may have a signal coming in that is slightly distorted due to the transmitting station being slightly off frequency OR because of an issue within your radio where the frequency tolerances are slightly off (radio need a tune up??) OR maybe just atmospheric conditions, etc.... So maybe you are on frequency 14.150 MHz but you are unable to hear the other station clearly. In this case use the Receiver Incremental Tuning (RIT) knob (or buttons) to swing up or down a bit to dial in (tune in) the signal and hear it more clearly. Your transmit signal would remain as 14.150 MHz but your receive might now be tuned to 14.152 MHz (for example).

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Tags: definitions radio operation hf arrl chapter 5 arrl module 11

What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?
  • Permits monitoring several modes at once
  • Correct Answer
    Permits noise or interference reduction by selecting a bandwidth matching the mode
  • Increases the number of frequencies that can be stored in memory
  • Increases the amount of offset between receive and transmit frequencies

What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?

Different modes use different amounts of bandwidth; if you are using a narrow receive bandwidth and the mode is wide FM, you will only "hear" a portion of the signal. On the other hand if you're using a wide FM receive bandwidth and the mode is narrow FM, you may not be able to make out the signal at all and there could be interference from other stations on nearby frequencies. The best signal will be experienced when the receiver is expecting the same amount of bandwidth that the transmitter is transmitting.

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Tags: radio operation bandwidth noise and interference hf arrl chapter 5 arrl module 11

Which of the following is an appropriate receive filter bandwidth for minimizing noise and interference for SSB reception?
  • 500 Hz
  • 1000 Hz
  • Correct Answer
    2400 Hz
  • 5000 Hz

SSB is Single Sideband From HamUniverse.com

The information contained in the average human voice needed to understand the voice is contained within about the first 3000hz of the human hearing range. Frequencies of the human voice beyond this range are not needed for communication purposes and are filtered out in the modulation process. So the average bandwidth of a SSB signal is about 3000hz wide with all of the voice characteristics needed within that range to be understandable.

Hearing Frequency Range Starting with the main frequency range, it is the frequency range of human hearing, which is responsible for the perception of speech. It covers the frequencies from 300 to 3000 Hz. The range of frequencies in which the intelligibility and the recognition of the tuning characteristics are concerned is between the above mentioned frequency. This frequency range is used for voice communication in telephony and is the range the human ear is the most sensitive. Because of this, a 2400Hz filter will generally leave enough of the voice characteristics to be understandable but filter out much of the noise. (See also http://www.seaindia.in/blog/human-voice-frequency-range/)

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Tags: filters ssb noise and interference hf arrl chapter 5 arrl module 11

Which of the following is an appropriate receive filter bandwidth for minimizing noise and interference for CW reception?
  • Correct Answer
    500 Hz
  • 1000 Hz
  • 2400 Hz
  • 5000 Hz

Morse code (or CW, Continuous Wave) communications use far less bandwidth than voice modes; because you only need to be able to definitely discern whether or not the carrier is there (so you can hear the on/off of the morse code) you need very little bandwidth and so your receive filter can be very small. In fact, question T8A11 states that the approximate minimum bandwidth required to transmit a CW signal is 150 Hz.

As a point to remember, any time you see a question regarding CW and bandwidth, CW will pretty much be the smallest number there. More information about CW bandwidth can be found here.

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Tags: noise and interference filters morse code arrl chapter 5 arrl module 11

What is the function of automatic gain control, or AGC?
  • Correct Answer
    To keep received audio relatively constant
  • To protect an antenna from lightning
  • To eliminate RF on the station cabling
  • An asymmetric goniometer control used for antenna matching

You can guess that an AGC has nothing to do with protecting from lightning or eliminating RF from the station cabling.

It's used to control the gain, automatically, so that when AM signals get stronger, they don't suddenly get louder. It smooths out the changes in audio level when the signal strength goes up and down, something that happens a lot on low bands with SSB signals (SSB is a type of AM).

A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry is derived from two Greek words, gōnia, meaning angle, and metron, meaning measure. Wikipedia. Nothing at all to do with an AGC. An asymmetric goniometer?

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Tags: repeater definitions arrl chapter 5 arrl module 11

Which of the following could be used to remove power line noise or ignition noise?
  • Squelch
  • Correct Answer
    Noise blanker
  • Notch filter
  • All of these choices are correct

Squelch would remove too much, not just the power line or ignition noise - it might remove the signal you're trying to hear.

A notch filter removes a signal at a specific frequency, but power line and ignition noise are typically heard on a range of frequencies, so a notch filter wouldn't remove that noise.

Since two of the distractors are wrong, it can't be All, so that leaves the Noise blanker, the right answer.

A noise blanker reduces impulse noise without significantly reducing the strength of non-impulse noise.

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Which of the following is a use for the scanning function of an FM transceiver?
  • To check incoming signal deviation
  • To prevent interference to nearby repeaters
  • Correct Answer
    To scan through a range of frequencies to check for activity
  • To check for messages left on a digital bulletin board

A scanning function is useful for scanning through a range of frequencies to check for activity. None of the other options have anything to do with scanning.

The scanning feature on a radio will rapidly switch receive frequencies automatically, pausing on each frequency for only a fraction of a second to see if a carrier signal is present indicating that someone is actively transmitting on that frequency. If no carrier is present on a frequency it continues to the next one.

If a carrier is present on a frequency then the action taken is usually user-configurable. Scanning features can typically be configured to stop on the frequency until manually told to continue, to stop for only a few seconds, or stop for as long as the carrier signal remains then continue. More sophisticated scanning features may have more advanced options. Scanners can often be configured to scan a list of specific frequencies (such as repeaters) rather than an incremental range.

As you can imagine, this can be very useful for finding other operators to communicate with when you have no idea what frequency they might be transmitting on.

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