Free Wireless Communications (WCM) Practice Questions

Sample Practice Questions

Try these 10 sample questions from the Wireless Communications (WCM) practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1How are the electric and magnetic fields oriented in a freely propagating radio wave?

   1. A.Parallel to each other and parallel to propagation
   2. B.Perpendicular to each other and transverse to propagationCorrect answer: B
   3. C.Parallel to each other and transverse to propagation
   4. D.Perpendicular to each other, with the electric field along propagation

   Explanation: The guide states, "both are perpendicular to each other" and "both are perpendicular to the direction in which the wave travels." Thus both fields are transverse, with mutually perpendicular orientations.

   Reference: Radio System Basics and RF Fundamentals — Chapter 2, p.12, The Nature of Electromagnetic Signals

2. 2A two-way radio reports its GPS position to dispatch. What role do the GPS satellites themselves perform in this arrangement?

   1. A.They broadcast reference signals that the radio receives.Correct answer: A
   2. B.They receive each radio's reported location and forward it to dispatch.
   3. C.They negotiate a return channel with each radio before providing a fix.
   4. D.They poll each radio's transmitter to measure its round-trip range.

   Explanation: GPS.gov states, "They are simply beacons, like lighthouses, broadcasting one-way reference signals." The radio can use those signals for positioning; reporting that position to dispatch is a separate communications function.

   Reference: GPS.gov Frequently Asked Questions — General: I lost my mobile phone/device. Can GPS help me find it?

3. 3A radio-system diagram labels a path with f_RX = 150.000 MHz. What does this label identify?

   1. A.The receiver's intermediate frequency
   2. B.The transmitter's operating frequency
   3. C.The receiver's operating frequencyCorrect answer: C
   4. D.The modulation signal's frequency

   Explanation: The guide states, "A receiver or the act of signal reception is often shortened to ‘RX’" and gives a receive-frequency example using f_RX. The subscript therefore identifies the receive operating frequency, rather than the transmitter, modulation, or IF frequency.

   Reference: Radio System Basics and RF Fundamentals — Chapter 3, p.48, Radio System Terminology

4. 4Which soldering accessory absorbs heat from a component lead to protect a heat-sensitive part?

   1. A.A solder wick
   2. B.A thermal shuntCorrect answer: B
   3. C.A flux applicator
   4. D.A wire-wrap bit

   Explanation: NASA describes thermal shunts as being used "to absorb heat from part leads". A wick removes solder, flux promotes wetting, and a wrapping bit forms a wire-wrap connection.

   Reference: NASA-STD-8739.3—Soldered Electrical Connections — 6.7, Thermal Shunts

5. 5Which software operation retrieves the actual programmed RF frequency, channel bandwidth, and signaling settings from a connected MT-4E radio before testing?

   1. A.Opening a previously saved maintenance report in a word processor
   2. B.Copying generic service-monitor presets without reading the radio
   3. C.Reading the receiver or transmitter with Radio Service SoftwareCorrect answer: C
   4. D.Viewing only the USB device name in the operating system

   Explanation: The guide instructs, "Read the transmitter or receiver programming" in RSS after making the USB connection. This retrieves the connected radio configuration; reports and generic presets can describe different or earlier settings, while the USB device name does not provide them.

   Reference: MT-4E Analog and P25 Digital Radio Systems Maintenance Guide — Chapter 5, p.19, Radio Service Software (RSS)

6. 6Approximately how fast does a radio wave travel through air under ordinary conditions?

   1. A.3 × 10^5 m/s
   2. B.3 × 10^6 m/s
   3. C.3 × 10^7 m/s
   4. D.3 × 10^8 m/sCorrect answer: D

   Explanation: The guide gives the speed of light as "2.9979 x 10 8 m/s". Radio propagation in air is approximately 3 × 10^8 m/s; the other choices are powers-of-ten errors.

   Reference: Antenna System Guide—NIJ Guide 202-00 — 3.2, Frequency and Wavelength, p.8

7. 7What RMS voltage level in microvolts corresponds to 60 dBµV?

   1. A.10 µV
   2. B.100 µV
   3. C.1,000 µVCorrect answer: C
   4. D.10,000 µV

   Explanation: TDK states, "1mV voltage is regarded as 60dBμV". One millivolt equals 1,000 microvolts. The voltage conversion uses a factor of 20 in the logarithm.

   Reference: TDK EMC Components FAQ—What is dBµV? — FAQ answer, voltage-level examples

8. 8What carries the control commands between a DC remote desk set and an IDA1000A adapter?

   1. A.An Ethernet packet's destination address.
   2. B.A sequence of audio-frequency guard tones.
   3. C.The magnitude and polarity of DC line current.Correct answer: C
   4. D.The received RF carrier's frequency deviation.

   Explanation: The manual describes stations "controlled from a remote desk set or console by dc line currents." Its different positive and negative current commands distinguish transmitter and monitor operations.

   Reference: GAI-Tronics IDA1000A DC Remote Adapter Installation and Service Manual — Operational Description, p.8

9. 9A technician needs to check a transmitter's carrier frequency, RF output power, and occupied bandwidth with one integrated instrument. Which instrument provides these functions?

   1. A.A time-domain reflectometer
   2. B.A broadband RF wattmeter
   3. C.A communications service analyzerCorrect answer: C
   4. D.A swept antenna impedance analyzer

   Explanation: The guide states that "a communications service monitor can determine whether a radio is transmitting on the proper frequency, at the proper power level, with the proper frequency bandwidth." This integrated instrument covers all three transmitter checks. A wattmeter measures power; the other analyzers characterize transmission paths or impedance.

   Reference: Antenna System Guide—NIJ Guide 202-00 — Maintenance and testing, communications service monitor

10. 10Under FCC Part 15, what interference obligations apply to a device, including interference it receives from authorized radio stations?

    1. A.It may cause harmful interference and reject incoming interference.
    2. B.It must cause no harmful interference and accept incoming interference.Correct answer: B
    3. C.It must cause no harmful interference but may reject incoming interference.
    4. D.It may cause harmful interference if it accepts incoming interference.

    Explanation: Section 15.5(b) requires that "no harmful interference is caused and that interference must be accepted". Both obligations apply; accepting interference does not permit causing harmful interference, and avoiding harmful emissions does not confer protection against authorized stations.

    Reference: 47 CFR §15.5—General conditions of operation — §15.5(b)