問71
頻出度★★★
携帯電話で用いられる電波に関する次の記述中の a，b に入れる字句の適切な組合せはどれか。 電波には，周波数が a ほど回り込みやすくなり障害物の裏にも届きやすいという性質がある。日本国内の携帯電話で使用される周波数のうち，700 b 帯～900 b 帯の周波数帯域はこの性質をもちつながりやすいことなどから，プラチナバンドと呼ばれている。
令和7年度 ITパスポート試験 問71
テクノロジ系ネットワーク › ネットワーク応用
This question's explanation and your answers so far.
解説
問 71
※ Our check while writing this explanation could not fully confirm the published answer; scoring follows IPA's official key.
Incorrectア
a = high is wrong. The higher the frequency (the shorter the wavelength), the stronger the straight-line travel and the harder it is to diffract, which contradicts the statement that it easily reaches behind obstacles. Furthermore, b = GHz is also wrong; the platinum band is the 700-900 MHz band.
Incorrectイ
a = high is wrong. The lower the frequency, the more easily diffraction occurs; at high frequencies it becomes hard to reach. b = MHz is correct, but because a is reversed, the combination is inappropriate.
Incorrectウ
a = low is correct, but b = GHz is wrong. The platinum band is the frequency band formed by adding MHz to the values 700-900; 700-900 GHz would be of a vastly different order of magnitude and does not exist.
- エ
正解 The lower the frequency of a radio wave, the longer its wavelength, and the more easily it diffracts around the edges of obstacles, so it more readily reaches places out of line of sight such as behind buildings. Therefore 'low' goes in a. The band with this property used by mobile phones in Japan is the 700-900 MHz band, and the unit is MHz, so 'MHz' goes in b. The combination of a = low and b = MHz is エ, which is the correct answer. This 700-900 MHz band is called the 'platinum band' because it connects easily and is highly valuable.
ここがポイント
- The lower the frequency of a radio wave (the longer the wavelength), the more easily it diffracts and reaches behind obstacles; conversely, high frequencies travel in straight lines and diffract less.
- The platinum band refers to the 700-900 MHz band, which is regarded as a highly valuable frequency band for mobile phones because it connects easily and has a wide coverage range.
用語