What frequency range is typically referred to as Extremely Low Frequency (ELF)?

The frequency range referred to as Extremely Low Frequency (ELF) is typically defined as 3 Hz to 30 Hz. ELF waves are used for various long-distance communication purposes, particularly in military applications, due to their ability to penetrate deep into the earth and water.

These low frequencies are particularly valuable for communication with submarines and other underwater applications because they can travel great distances without significant attenuation. This is in contrast to higher frequencies, which have more limited range and penetration capabilities.

While the other frequency ranges listed are associated with other designations (such as very low frequency (VLF) for 3 kHz to 30 kHz), they do not fall under the ELF category. Hence, the proper definition and application of ELF frequencies are crucial for understanding communication systems that utilize these low frequencies.