LESSON 8

SUBELEMENT T4 - Amateur radio practices and station set up – [2 Exam Questions - 2 Groups]

Lesson 8a

T4A – Station setup; microphone, speaker, headphones, filters, power source, connecting a computer, RF grounding

When hooking up a new microphone to a transmitter or transceiver you need to be sure the new microphone is compatible with the unit it is being connected to. Some microphones need power to run amplifiers that are enclosed in the microphone’s case. So some transceiver microphone connecters include voltage for powering the microphone and also a push-to-talk circuit.

Sometimes when operating in a noisy area it can be difficult to hear and understand a speaker. In times like that a set of headphones can be used in place of a regular speaker.

When using an external power supply to operate a piece of communication equipment it should be a regulated power supply that means the voltage will remain constant with a varying load. It is normal for a transmitter to draw a much larger current then a receiver and if both are operated off the same power supply whether separate units or combined in a transceiver the voltage should not change significantly when going from receive to transmit and back. A regulated power supply prevents voltage fluctuations from reaching sensitive circuits.

A water filter removes unwanted elements from water and an RF filter removes unwanted elements from radio signals. High-pass filters allow radio signals above a given cutoff point to pass with little attenuation while it rejects all radio signals below the cutoff frequency. A low-pass filter is the inverse of a high-pass filter. It rejects all RF signals above a cutoff frequency while passing those below that. A band-pass filter has a lower frequency cutoff point and an upper cutoff frequency so it rejects all RF signals except those signals between the two cutoff points. A band-reject filter allows all RF signals to pass except those that fall within the lower and upper cutoff point. These filters are designed to help reduce interference.

Harmonic emissions are multiples of the fundamental frequency so they are always higher then the fundamental frequency. To reduce harmonic emissions from a transmitter a low-pass filter can be placed between the transmitter and the antenna. It is best to place it as close to the transmitter as possible.

If a nearby 2 meter transmitter overloads a TV receiver and both are operating properly the cause is most likely fundamental overload. The first step that can be taken to try to prevent the TV receiver from being affected by the RF overload is to install a band-reject filter that rejects those frequencies of 144 to 148 MHz between the TV and its antenna. The filter should be as close to the TV input as possible.

If RF current is flowing on the shield of an audio cable it can create distortion or other possible problems. Powdered iron glued together can be used to make forms or beads that when the audio cable is wrapped around these Ferrite cores will greatly increase the inductive reactance at RF frequencies. Remember inductive reactance becomes higher as the frequency is increased. So a Ferrite choke can be used to reduce RF current flowing on the shield of an audio cable without significantly affecting the audio frequencies.

Though rarely used because it is difficult to find and difficult to work with a flat strap is the best type of conductor to use for RF grounding.

Digital communications requires the interfacing of a transceiver with a computer. To run a packet radio station (a form of digital communications) a terminal node controller needs to be connected between a transceiver and the computer. The computer’s sound card is used when conducting digital communications to provide audio to the microphone input and convert received audio to digital form for the computer.

Sometimes a high-pitched whine that varies with engine speed can be heard in a mobile transceiver’s receive audio. The source of such noise is the vehicle’s alternator.

Whether I agree or disagree with the answer to a question given in the question pool does not really matter much I still need to give you the answer they want if I am to help you pass the test.

Question T4A11 asks, “Where should a mobile transceiver’s power negative connection be made?” The answer they want is, “A. At the battery or engine block ground strap.” If you follow their instructions please put a fuse in the negative lead to reduce the potential of a fire in your vehicle. (To learn more about this go to http://hamslife.com/?p=106)

*T4A01
Which of the following is true concerning the microphone connectors on amateur transceivers?
A. All transceivers use the same microphone connector type
B. Some connectors include push-to-talk and voltages for powering the microphone
C. All transceivers using the same connector type are wired identically
D. Un-keyed connectors allow any microphone to be connected
~~

*T4A02
What could be used in place of a regular speaker to help you copy signals in a noisy area?
A. A video display
B. A low pass filter
C. A set of headphones
D. A boom microphone
~~

*T4A03
Which is a good reason to use a regulated power supply for communications equipment?
A. It prevents voltage fluctuations from reaching sensitive circuits
B. A regulated power supply has FCC approval
C. A fuse or circuit breaker regulates the power
D. Power consumption is independent of load
~~

*T4A04
Where must a filter be installed to reduce harmonic emissions?
A. Between the transmitter and the antenna
B. Between the receiver and the transmitter
C. At the station power supply
D. At the microphone
~~

*T4A05
What type of filter should be connected to a TV receiver as the first step in trying to prevent RF overload from a nearby 2 meter transmitter?
A. Low-pass filter
B. High-pass filter
C. Band-pass filter
D. Band-reject filter
~~

*T4A06
Which of the following would be connected between a transceiver and computer in a packet radio station?
A. Transmatch
B. Mixer
C. Terminal node controller
D. Antenna
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*T4A07
How is the computer’s sound card used when conducting digital communications using a computer?
A. The sound card communicates between the computer CPU and the video display
B. The sound card records the audio frequency for video display
C. The sound card provides audio to the microphone input and converts received audio to digital form
D. All of these choices are correct
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*T4A08
Which type of conductor is best to use for RF grounding?
A. Round stranded wire
B. Round copper-clad steel wire
C. Twisted-pair cable
D. Flat strap
~~

*T4A09
Which would you use to reduce RF current flowing on the shield of an audio cable?
A. Band-pass filter
B. Low-pass filter
C. Preamplifier
D. Ferrite choke
~~

*T4A10
What is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’s receive audio?
A. The ignition system
B. The alternator
C. The electric fuel pump
D. Anti-lock braking system controllers
~~

*T4A11
Where should a mobile transceiver’s power negative connection be made?
A. At the battery or engine block ground strap
B. At the antenna mount
C. To any metal part of the vehicle
D. Through the transceiver’s mounting bracket
~~

Answers:
B, C, A, A, D, C, C, D, D, B, A

Lesson 8 b

T4B - Operating controls; tuning, use of filters, squelch, AGC, repeater offset, memory channels

The first radio most hams get today is a 2 meter handheld so they can operate through a local repeater. Repeaters receive a signal on a certain frequency called the input frequency and simultaneously transmit the audio it receives on a different frequency called the output frequency. The difference between the repeater’s receive and transmit is called the “repeater offset.”

Some modern transceivers still use a VFO knob to set the operating frequency and others use a keypad to set the operating frequency. There are some that have the ability to set the operating frequency using either the VFO knob or the keypad.

Excessive microphone gain can cause over modulation on AM, excessive deviation on FM, and flat topping on SSB all of which can result in the output signal becoming distorted.

FM receiver detectors produce a very annoying white sound when no signal is being received. The squelch control on a transceiver is used to mute the receiver’s output noise when no signal is being received. As you adjust the squelch control it will have a point at which the receiver’s white noise will disappear when rotated in one direction and reappear when rotated in the other. The proper position for the squelch control to be set is the point where the white noise just disappears. Turning the squelch control too far may result in not hearing week signals.

Most modern transceivers have a way to store your favorite frequencies or those frequencies you need to access quickly in memory channels. So a way to enable quick access to a favorite frequency on your transceiver is store the frequency in a memory channel.

To understand a single-sideband signal the BFO which provides the insertion frequency to the product detector must be within a very few Hertz of the carrier frequency which the transmitter has removed. Though your receiving frequency, as read on the frequency readout, may read the same as the transmitting station’s transmitter frequency readout they can easily be off by a several Hertz. The Receiver Incremental Tuning (RIT) control sometimes called “clarifier” allows the receiver to be adjusted to compensate for this difference. This control is used when the voice pitch of a single-sideband signal seems too high or too low.

Having multiple receiver bandwidth choices on a multimode transceiver or receiver permits noise or interference reduction by selecting the bandwidth matching the mode you are using. An appropriate receiver filter selection in order to minimize noise and interference for SSB reception is 2400 Hz and for CW reception is 500 Hz.

A noise blanker, if available on a receiver, can reduce certain types of interferences such as ignition interference.

*T4B01
What may happen if a transmitter is operated with the microphone gain set too high?
A. The output power might be too high
B. The output signal might become distorted
C. The frequency might vary
D. The SWR might increase
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*T4B02
Which of the following can be used to enter the operating frequency on a modern transceiver?
A. The keypad or VFO knob
B. The CTCSS or DTMF encoder
C. The Automatic Frequency Control
D. All of these choices are correct
~~

*T4B03
What is the purpose of the squelch control on a transceiver?
A. To set the highest level of volume desired
B. To set the transmitter power level
C. To adjust the automatic gain control
D. To mute receiver output noise when no signal is being received
~~

*T4B04
What is a way to enable quick access to a favorite frequency on your transceiver?
A. Enable the CTCSS tones
B. Store the frequency in a memory channel
C. Disable the CTCSS tones
D. Use the scan mode to select the desired frequency
~~

*T4B05
Which of the following would reduce ignition interference to a receiver?
A. Change frequency slightly
B. Decrease the squelch setting
C. Turn on the noise blanker
D. Use the RIT control
~~

*T4B06
Which of the following controls could be used if the voice pitch of a single-sideband signal seems too high or low?
A. The AGC or limiter
B. The bandwidth selection
C. The tone squelch
D. The receiver RIT or clarifier
~~

*T4B07
What does the term "RIT" mean?
A. Receiver Input Tone
B. Receiver Incremental Tuning
C. Rectifier Inverter Test
D. Remote Input Transmitter
~~

*T4B08
What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?
A. Permits monitoring several modes at once
B. Permits noise or interference reduction by selecting a bandwidth matching the mode
C. Increases the number of frequencies that can be stored in memory
D. Increases the amount of offset between receive and transmit frequencies
~~

*T4B09
Which of the following is an appropriate receive filter to select in order to minimize noise and interference for SSB reception?
A. 500 Hz
B. 1000 Hz
C. 2400 Hz
D. 5000 Hz
~~

*T4B10
Which of the following is an appropriate receive filter to select in order to minimize noise and interference for CW reception?
A. 500 Hz
B. 1000 Hz
C. 2400 Hz
D. 5000 Hz
~~

*T4B11
Which of the following describes the common meaning of the term “repeater offset”?
A. The distance between the repeater’s transmit and receive antennas
B. The time delay before the repeater timer resets
C. The difference between the repeater’s transmit and receive frequencies
D. The maximum frequency deviation permitted on the repeater’s input signal
~~

Answers:
B, A, D, B, C, D, B, B, C, A, C,