1. This depends on the precise radio- frequency of the 21- cm wavelength, or 1420 megacycles per second .
    这种方法依靠21厘米波长或每秒1420兆周的精确无线电频率。

2. This depends on the precise radio- frequency of the 21- cm wavelength, or 1420 megacycles per second .
    这种方法依靠21厘米波长或每秒1420兆周的精确无线电频率。

3. This depends on the precise radio frequency of the 21-cm wavelength, or 1420 megacycles per second.
    这种通迅联系要靠21厘料波段，即每秒1420兆周的精确无线电频率。