In radio communications, which frequency range is officially designated as the high frequency (HF) band?

Introduction / Context:
The radio spectrum is divided into different bands, each covering a specific frequency range and used for particular communication services. Knowing the names and ranges of these bands is important in basic electronics, communication engineering and general science exams. This question asks you to identify the frequency limits of the high frequency (HF) band, which is widely used for long-distance shortwave radio communication.

Given Data / Assumptions:

• The options list several different frequency values and ranges.
• The HF band has a standard definition agreed by international bodies.
• We assume frequencies are measured in megahertz (MHz) or kilohertz (kHz) as indicated.
• We must match the official HF band range from among the choices.

Concept / Approach:
The International Telecommunication Union (ITU) classifies radio frequencies into named bands such as very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF) and so on. The high frequency (HF) band is defined as the range from 3 MHz to 30 MHz. These frequencies are often called shortwave and can support long-distance communication by reflecting off the ionosphere. Frequencies below this range fall into MF and LF bands, while frequencies above it fall into VHF and higher bands.

Step-by-Step Solution:
Step 1: Recall or look up the standard classification of radio frequency bands.Step 2: Note that HF stands for high frequency and covers 3 to 30 MHz.Step 3: Compare this with the option 3 kHz, which is far too low and would belong to much lower frequency bands.Step 4: Check the option 30 to 300 MHz, which corresponds more closely to very high frequency (VHF) and parts of ultra high frequency (UHF), not HF.Step 5: Recognise that 10 GHz lies in the microwave region, well above the HF range.Step 6: Conclude that only the range 3 to 30 MHz correctly represents the HF band.

Verification / Alternative check:
Amateur radio operators and shortwave broadcasters frequently refer to HF as the 3 to 30 MHz shortwave region. Technical references on ionospheric propagation also use this definition, explaining how signals in this band can travel beyond the horizon by skywave propagation. The consistency of this definition across multiple sources confirms that HF corresponds to 3 to 30 MHz.

Why Other Options Are Wrong:
3 kHz alone is a single frequency, not a band, and lies in audio or very low radio frequency regions, not in HF. The 30 to 300 MHz range covers VHF and part of UHF, used for FM radio, television and some mobile services. A frequency of 10 GHz is in the microwave band and is used for radar, satellite communication and certain wireless links, not HF.

Common Pitfalls:
Students sometimes mix up the alphabetic labels HF, VHF and UHF because they all contain the word frequency. Others may memorise the ranges incorrectly or confuse MHz with kHz or GHz. To avoid these errors, remember the key figures: HF is 3 to 30 MHz, VHF is 30 to 300 MHz and UHF is 300 MHz to 3 GHz.

Final Answer:
The high frequency (HF) band in radio communications spans from 3 MHz to 30 MHz.