Very Low Frequency (VLF) waves we refer to groundwaves, unlike Very High Frequency (VHF) the frequency is a large amount of groundwaves and only a very small amount of skywaves.
Why would we want this at all, you ask? If we want to transmit a signal large distances, following the earth’s curvature and not have to worry largely about line of sight then we would choose a VLF.
Can you think of a instrument we use in the aircraft, that uses a VLF?
If you answered the ADF (Automatic Direction Finding) paired with a NDB (Non-Directional Beacon) you’d be correct!
We’ll go into those shortly, but for now remember this: low frequency, groundwaves, large distances.