It's easier to find and acquire jamming equipment for some frequencies than it is for others.
2016年12月四级真题（第一套）阅读 Section B
Security devices are required to list the frequencies they broadcast on—that means that a potential thief can find what they need to know with minimal Googling.
2016年12月四级真题（第一套）阅读 Section B
英语六级真题
The department will make sure that newly launched satellites don't use radio frequencies that would interfere with existing satellites, and schedule when such new satellites can be launched.
2019年6月六级真题（第二套）阅读 Section C
柯林斯高阶英汉双解学习词典释义
N-UNCOUNT
频率;发生次数
The frequency of an event is the number of times it happens during a particular period.