Extremely low frequency and Radio frequency

Extremely low frequency noun - Below 3 kilohertz.

Radio frequency and extremely low frequency are semantically related. In some cases you can use "Radio frequency" instead a noun phrase "Extremely low frequency".

Radio frequency noun - An electromagnetic wave frequency between audio and infrared.

Extremely low frequency and radio frequency are semantically related. Sometimes you can replace phrase "Extremely low frequency" with "Radio frequency", this phrases are similar.