___________ use radio waves to transmit voice communication in the ultrahigh frequency band.
Cellular phones
The question asks to identify the technology that uses radio waves to transmit voice communication specifically within the ultrahigh frequency (UHF) band. Let's examine each option to determine which one best fits this description.
Cellular Phones and UHF Communication
Cellular phones are devices designed for two-way personal communication, allowing users to make and receive calls. They are a prime example of a technology that utilizes radio waves for voice communication over wireless networks. Here's why they are the correct answer:
- Frequency Band: Cellular networks operate across various frequency bands, including significant portions of the ultrahigh frequency (UHF) band (which typically ranges from 300 MHz to 3 GHz) and even higher frequency microwave bands (e.g., for 4G and 5G technologies). This aligns directly with the "ultrahigh frequency band" mentioned in the question.
- Voice Communication: The fundamental purpose of a cellular phone is to enable real-time, two-way voice communication between individuals.
- Radio Waves: All cellular communication, whether voice or data, is transmitted wirelessly using radio waves between the phone and cellular base stations.
Radio Wave Communication Technologies
Let's consider the other options to understand why they do not precisely fit the description:
AM Radio Transmission
- AM (Amplitude Modulation) radio is primarily used for one-way broadcasting of audio programs.
- It typically operates in the medium frequency (MF) band (e.g., 535 kHz to 1705 kHz) and high frequency (HF) band (e.g., 3 MHz to 30 MHz).
- These frequency ranges are significantly lower than the ultrahigh frequency (UHF) band, and AM radio is not used for two-way personal voice communication.
FM Radio Transmission
- FM (Frequency Modulation) radio is also used for one-way broadcasting of high-fidelity audio.
- Commercial FM broadcasting typically operates in the very high frequency (VHF) band, specifically from 88 MHz to 108 MHz.
- While higher than AM, the standard FM broadcast band is still below the typical range of the ultrahigh frequency (UHF) band, and it does not facilitate two-way personal voice communication.
TV Waves Transmission
- TV waves refer to the radio signals used for television broadcasting. Television broadcasts utilize both the very high frequency (VHF) band and the ultrahigh frequency (UHF) band.
- Although TV waves use the UHF band, their purpose is for one-way broadcasting of video and audio content to a wide audience, not for interactive, two-way personal voice communication between individuals. A television receiver simply receives signals and does not transmit voice back for a conversation.
Voice Communication Technology Comparison
The table below summarizes how each technology relates to the requirements of the question:
| Technology | Uses Radio Waves | Primary Purpose | Operates in UHF Band | Supports Two-Way Voice Communication |
|---|---|---|---|---|
| AM Radio | Yes | One-way audio broadcast | No (MF/HF) | No |
| FM Radio | Yes | One-way audio broadcast | No (VHF) | No |
| TV Waves | Yes | One-way video/audio broadcast | Yes | No (only receives broadcast audio) |
| Cellular Phones | Yes | Two-way voice & data communication | Yes | Yes, extensively |
Based on this analysis, only cellular phones fit all criteria: they use radio waves, are designed for voice communication, and operate extensively in the ultrahigh frequency band for two-way interaction.
Important Questions from Communication Systems
A microphone converts
- An AM radio station transmits with a modulation frequency of $250 \text{ kHz}$, which represents $10\%$ of its carrier wave frequency. To ensure clear reception and prevent adjacent channel interference, broadcasting regulations stipulate that the entire bandwidth of any new station must not overlap with the bandwidth of an existing station. If a new license application is filed for an AM station requiring a *lower* carrier frequency than the existing station, what is the *highest* possible carrier frequency (in $\text{kHz}$) that can be allotted to this new station without causing interference?
For a generalised communication system, arrange the following in the correct sequence :
(A) Receiver
(B) Information source
(C) Channel
(D) User of information
(E) Transmitter
Choose the correct answer from the options given below:
Consider the following types of modulation:
(i) Amplitude modulation
(ii) Frequency modulation
(iii) Phase modulation
(iv) Pulse modulation
Which of the above modulations are used for telecasting TV programs?
- Give an example of means of personal communication.
