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Chapter 28: Problem 30

A communication between a fixed base station and several mobile units, located on ships or aircraft utilising two way radio communication in the VHF and UHF is of frequency band (a) 3 to \(30 \mathrm{MHz}\) (b) 30 to \(300 \mathrm{MHz}\) (c) 30 to \(470 \mathrm{MHz}\) (d) 30 to \(600 \mathrm{MHz}\)

Short Answer

Expert verified
Option (c) is correct: 30 to 470 MHz.

Step by step solution

01

Identify the Frequency Bands

First, identify the main frequency bands used for Very High Frequency (VHF) and Ultra High Frequency (UHF) radio communication: VHF is typically from 30 to 300 MHz, and UHF is from 300 MHz to 3 GHz.
02

Analyze the Options

Now analyze each given option: - (a) 3 to 30 MHz: This range is classified as High Frequency (HF), not applicable here. - (b) 30 to 300 MHz: This lies entirely within the VHF range. - (c) 30 to 470 MHz: This includes the upper VHF range as well as part of the UHF range. - (d) 30 to 600 MHz: This covers VHF and extends further into the UHF range.
03

Verify Two-Way Radio Communication Band

Verify that two-way radio communication for ships or aircraft in the context of the problem commonly uses both VHF and lower UHF bands, which correspond to 30-300 MHz for VHF and 300-470 MHz for lower ranges of UHF.
04

Select the Correct Answer

Options (c) and (d) both cover the VHF band and extend into UHF. The context of "ships or aircraft" and the use of two-way communication helps indicate that the range might not vastly exceed necessary bands, thus considering practical usage up to 470 MHz makes option (c) the most reasonable choice.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

radio communication
Radio communication is a method of sending and receiving information wirelessly using radio waves. This process is invisible to the human eye. Instead, it relies on electromagnetic waves to carry messages over both short and long distances.
Radio communication systems are essential for various applications spanning different fields.
  • In public broadcasting, they transmit audio programs across vast regions.
  • They are vital in emergency services for coordination during critical events.
  • Military operations use radio communication to maintain secure and effective contact in the field.
Radio communication relies on transmitting devices to send out radio waves, which are captured by receiving devices. Effective communication depends on the correct tuning of frequency bands by both sender and receiver.
two-way radio systems
Two-way radio systems allow for reciprocal communication, meaning both parties can send and receive messages. Unlike traditional broadcasting which is one-way, these systems support interactive dialogue.
These systems are classified based on the type of communication they facilitate:
  • Simplex: Communication occurs in one direction at a time, like a walkie-talkie.
  • Half-duplex: Supports two-way communication but not simultaneously.
  • Full-duplex: Allows two-way communication simultaneously, similar to a phone call.
Two-way radio systems are commonly used in:
  • Public safety organizations - for coordinated operations between departments.
  • Transportation industries - enabling drivers and dispatch to stay connected.
  • Large events - coordinators can manage logistics efficiently.
These systems operate in various frequency bands, particularly utilizing VHF and UHF to ensure clear communication over appropriate distances.
frequency bands identification
Frequency bands define specific ranges of frequencies used for radio transmission. They are critical to ensure harmony and avoid interference between different technologies.
Key bands in radio communication include:
  • Very High Frequency (VHF): Ranges from 30 to 300 MHz. Suitable for both long-distance communication and local radio broadcasts due to its ability to travel beyond the horizon.
  • Ultra High Frequency (UHF): Ranges from 300 MHz to 3 GHz. Offers high bandwidth with less atmospheric attenuation, ideal for TV broadcasting, mobile phones, and GPS units.
  • High Frequency (HF): Covers 3 to 30 MHz and is suited for long-distance communication over oceans or remote places.
Identifying these bands ensures systems operate without interference, maintaining signal quality, and efficiency.
communication systems in ships and aircraft
Communication systems in ships and aircraft are essential for safe and efficient operations. These systems rely heavily on radio communication within specific frequency bands. For shipping and maritime operations:
  • VHF radio is commonly used for short to medium range communication, such as between ships or from ship to shore.
  • UHF can be employed for more localized intra-ship communications where line-of-sight is feasible.
In aviation:
  • VHF communication supports pilot to air traffic control (ATC) messaging, essential for air safety.
  • For in-cabin and ground communications, UHF might be used due to its effectiveness over short distances without interference.
  • HF can be utilized for long-range communication when traversing international waters or remote geographic locations.
Operating within these defined bands helps mitigate communication challenges due to atmospheric conditions or physical obstructions, ensuring reliable connectivity.

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Most popular questions from this chapter

A message signal of frequency \(\omega_{m}\) is superposed on a carrier wave of frequency 0 , to get an amplitude modulated wave (AM). The frequency of the AM wave will be (a) \(\omega_{-1}\) (b) \(\omega_{f}\) (c) \(\frac{\underline{\omega}_{z}+\omega_{m}}{2}\) (d) \(\frac{\omega_{c}-\omega_{1}}{2}\)

The ratio of critical frequency for reflection of radiowaves from \(E, F_{1}\) and \(F_{2}\) layers in ionosphere of earth's atmosphere is (a) \(\sqrt{2}: \sqrt{3}: \sqrt{8}\) (b) \(2: 3: 8\) (c) \(\frac{1}{2}: \frac{1}{3}: \frac{1}{8}\) (d) \(\frac{1}{4}: \frac{1}{9}: \frac{1}{84}\)

The highest frequency of radiowaves which when sent at some angle towards the ionosphere, gets reflected from that and returns to the earth is called (a) critical frequency (b) maximum unusable frequency (c) polarisation of waves (d) None of the above

The total power content of AM wave is \(900 \mathrm{~W}\). For \(100 \%\) modulation, the power transmitted by each size band is (a) \(150 \mathrm{~W}\) (b) \(140 \mathrm{~W}\) (c) \(100 \mathrm{~W}\) (d) \(90 \mathrm{~W}\)

Fading is the variation in the strength of a signal at a receiver due to (a) interference of waves (b) diffraction of waves (c) polarisation of waves (d) None of these
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