W4CA

Roanoke Valley Amateur Radio Club

T-7

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Subelement T7

Setting up, testing and troubleshooting your radio station.

 

A unit combining the functions of a transmitter and a receiver is a transceiver. “PTT” is the push to talk function, which switches between receive and transmit. Selectivity is the ability of a receiver to discriminate between multiple signals. The ability of a receiver to detect the presence of a signal is sensitivity. A Transverter takes the output of a low-powered 28 MHz SSB exciter and produces a 222 MHz output signal. A multi-mode VHF transceiver is useful for VHF weak-signal communication. RF power amplifier increases the low-power output from a handheld transceiver. RF preamplifier is installed between the antenna and receiver. To prevent the radiation of signals when making tests use a dummy load. A dummy load consists of a non-inductive resistor and a heat sink. An antenna analyzer is used to determine if an antenna is resonant at the desired operating frequency. FM handheld or mobile transceiver is over-deviating; talk farther away from the microphone. Your transmitter is slightly off frequency, Your batteries are running low or you’re in a bad location you will receive a report that your audio signal through the repeater is distorted or unintelligible.

Modulation describes combining speech with an RF carrier signal. Mixer is used to convert a radio signal from one frequency to another. Oscillator is the name of a circuit that generates a signal of a desired frequency.

Reports of garbled, distorted, or unintelligible transmissions are a symptom of RF feedback in a transmitter or transceiver. Fundamental overload, Harmonics and Spurious emissions cause radio frequency interference. A broadcast AM or FM radio will receive an amateur radio transmission unintentionally because it is unable to reject strong signals outside the AM or FM band. Overload of a non-amateur radio or TV receiver by an amateur signal can be reduced or eliminated by a filter at the antenna input of the affected receiver. Snap-on ferrite chokes; Low-pass and high-pass filters and band-reject and band-pass filters are useful in correcting a radio frequency interference problem.

If a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception, make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel. If something in a neighbor’s home is causing harmful interference to your amateur station, work with your neighbor to identify the offending device, politely inform your neighbor about the rules that prohibit the use of devices, which cause interference and check your station and make sure it meets the standards of good amateur practice. Part 15 device is an unlicensed device that may emit low powered radio signals on frequencies used by a licensed service.

A measure of how well a load is matched to a transmission line is the standing wave ratio (SWR). Directional wattmeter is used to determine if a feed line and antenna are properly matched. 1 to 1 on an SWR meter indicates a perfect impedance match between the antenna and the feed line. An SWR reading of 4 to 1 indicates an impedance mismatch. 2 to 1 is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power.

Carrying RF signals between a radio and antenna is a common use of coaxial cable. The outer jacket of coaxial cable is resistant to ultraviolet light so it will not damage the jacket and allow water to enter the cable. Moisture contamination is the most common cause for failure of coaxial cables. The disadvantage of air core coaxial cable compared to foam or solid dielectric types it requires special techniques to prevent water absorption. Power lost in a feed line is converted into heat.

A voltmeter is used measure electric potential or electromotive force. Connect a voltmeter in parallel to the circuit. Ensure that the voltmeter and leads are rated for use at the voltages to be measured when measuring high voltages with a voltmeter. An ammeter is used to measure electric current. An ammeter usually connected in series with the circuit. An ohmmeter is used to measure resistance. Ensure that the circuit is not powered when measuring circuit resistance with an ohmmeter. The circuit contains a large capacitor if when an ohmmeter, connected across an unpowered circuit, initially indicates a low resistance and then shows increasing resistance with time. Voltage and resistance measurements are commonly made using a multimeter. Attempting to measure voltage when using the resistance setting will damage a multimeter.

Rosin-core solder is best for radio and electronic use. A grainy or dull surface is the characteristic appearance of a cold solder joint.

A RF filter on the telephone is a way to reduce or eliminate interference by an amateur transmitter.

Be sure all TV coaxial connectors are installed properly to resolve cable TV interference from your ham radio transmission.

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SUBELEMENT T7

Station equipment: common transmitter and receiver problems; antenna measurements; troubleshooting; basic repair and testing

[4 Exam Questions – 4 Groups]

Which term describes the ability of a receiver to detect the presence of a signal?

  1. Sensitivity

What is a transceiver?

  1. A unit combining the functions of a transmitter and a receiver

Which of the following is used to convert a radio signal from one frequency to another?

  1. Mixer

Which term describes the ability of a receiver to discriminate between multiple signals?

  1. Selectivity

What is the name of a circuit that generates a signal at a specific frequency?

  1. Oscillator

What device converts the RF input and output of a transceiver to another band?

  1. Transverter

What is meant by “PTT”?

  1. The push-to-talk function that switches between receive and transmit

Which of the following describes combining speech with an RF carrier signal?

  1. Modulation

What is the function of the SSB/CW-FM switch on a VHF power amplifier?
B. Set the amplifier for proper operation in the selected mode

What device increases the low-power output from a handheld transceiver?

  1. An RF power amplifier

Where is an RF preamplifier installed?

  1. Between the antenna and receiver

What can you do if you are told your FM handheld or mobile transceiver is over-deviating?

  1. Talk farther away from the microphone

What would cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally?

  1. The receiver is unable to reject strong signals outside the AM or FM band

Which of the following can cause radio frequency interference?

Fundamental overload, Harmonics, Spurious emissions can cause radio frequency interference

Which of the following is a way to reduce or eliminate interference from an amateur transmitter to a nearby telephone?

  1. Put an RF filter on the telephone

How can overload of a non-amateur radio or TV receiver by an amateur signal be reduced or eliminated?

  1. Block the amateur signal with a filter at the antenna input of the affected receiver

Which of the following actions should you take if a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception?

  1. Make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel

Which of the following can reduce overload to a VHF transceiver from a nearby FM broadcast station?

  1. Band-reject filter

If something in a neighbor’s home is causing harmful interference to your amateur station; Work with your neighbor to identify the offending device, Politely inform your neighbor about the rules that prohibit the use of devices that cause interference, Check your station and make sure it meets the standards of good amateur practice.

What is a Part 15 device?

  1. An unlicensed device that may emit low-powered radio signals on frequencies used by a licensed service

If you receive a report that your audio signal through the repeater is distorted or unintelligible; Your transmitter is slightly off frequency, Your batteries are running low or You are in a bad location

What is a symptom of RF feedback in a transmitter or transceiver?

  1. Reports of garbled, distorted, or unintelligible voice transmissions

What should be the first step to resolve cable TV interference from your ham radio transmission?

  1. Be sure all TV coaxial connectors are installed properly

What is the primary purpose of a dummy load?

  1. To prevent transmitting signals over the air when making tests

Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency?

  1. An antenna analyzer

What, in general terms, is standing wave ratio (SWR)?

  1. A measure of how well a load is matched to a transmission line

What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?

  1. 1 to 1

Why do most solid-state amateur radio transmitters reduce output power as SWR increases?

  1. To protect the output amplifier transistors

What does an SWR reading of 4:1 indicate?

  1. Impedance mismatch

What happens to power lost in a feed line?

  1. It is converted into heat

What instrument other than an SWR meter could you use to determine if a feed line and antenna are properly matched?

  1. Directional wattmeter

Which of the following is the most common cause for failure of coaxial cables?

  1. Moisture contamination

Why should the outer jacket of coaxial cable be resistant to ultraviolet light?

  1. Ultraviolet light can damage the jacket and allow water to enter the cable

What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types?

  1. It requires special techniques to prevent water absorption

What does a dummy load consist of?

  1. A non-inductive resistor and a heat sink

Which instrument would you use to measure electric potential or electromotive force?

  1. A voltmeter

What is the correct way to connect a voltmeter to a circuit?

  1. In parallel with the circuit

How is a simple ammeter connected to a circuit?

  1. In series with the circuit

Which instrument is used to measure electric current?

  1. An ammeter

What instrument is used to measure resistance?

  1. An ohmmeter

Which of the following might damage a multimeter?

  1. Attempting to measure voltage when using the resistance setting

Which of the following measurements are commonly made using a multimeter?

  1. Voltage and resistance

Which of the following types of solder is best for radio and electronic use?

  1. Rosin-core solder

What is the characteristic appearance of a cold solder joint?

  1. A grainy or dull surface

What is probably happening when an ohmmeter, connected across an unpowered circuit, initially indicates a low resistance and then shows increasing resistance with time?

  1. The circuit contains a large capacitor

Which of the following precautions should be taken when measuring circuit resistance with an ohmmeter?

  1. Ensure that the circuit is not powered

Which of the following precautions should be taken when measuring high voltages with a voltmeter?

  1. Ensure that the voltmeter and leads are rated for use at the voltages to be measured

 

 

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