Electromagnetic Wave Propagation

[José M. Rico]

Electromagnetic waves, or radio waves, widely used for naval communications, travel through the atmosphere differently depending on their frequency.

UHF = Ultra High Frequency (from 300 to 3000 MHz) = Dezimeterwelle
VHF = Very High Frequency (from 30 to 300 MHz) = UKW (Ultrakurzwelle)
HF = High Frequency (from 3 to 30 MHz) = KW (Kurzwelle)
MF = Medium Frequency (from 300 to 3000 KHz) = MW (Mittelwelle)
LF = Low Frequency (from 30 to 300 KHz) = LW (Langwelle)
VLF = Very Low Frequency (from 3 to 30 KHz) = Längstwelle

UHF and VHF waves travel following a straight line under normal conditions, and are mainly used for "line-of-sight" communications. Therefore, signals sent under these frequencies can only be received by other ships (or planes) that are within the horizon of the transmitter ship. Both the transmitter and receiver must be within 25-30 miles of each other. These communications are relatively secure and normally won't be detected by an enemy that is not in sight.

HF and MF waves are transmitted with a certain angle of elevation and reach the Ionosphere where they bounce and return to earth hundreds of miles from the transmitting point. The use of HF frequencies makes it possible to establish contact with ships or land-based radio stations from very long distances. However these signals can also be picked up by the enemy.

LF and VLF waves travel along the surface of the earth/sea, penetrating several meters deep. This allows to send messages to submarines that can receive them without having to come up to the surface. The use of these frequencies requires the utilization of big antennas with a high power output.

[Ulrich Rudofsky]

It should be noted that I and others have on occasion mistranslated “UKW” as “UHF”. UKW (Ultrakurzwelle) is VHF (Very High Frequency) - 30MHz-300MHz. Dm-W (Dezimeterwellen) is UHF (Ultra High Frequency) – 300MHz-3GHz.