Distinctive channels have diverse qualities and shortcoming.
4. Decoder: Decoder translates the encoded message to recover the original message. This procedure has to be correct and accurate, or else the message is lost completely. This encoding and decoding will be exceptionally help full in military and versatile correspondences.
a) Super Low and Extra Low Frequency bands (SLF and ELF) normally occur natural. This can be very long antennae used by electricity authorities, called power lines radiating 50 or 60 Hz. The signal is experienced as hum. The largest natural source of this radio wave is the interaction between the solar wind and the ionosphere, which results in low frequency currents in the earth and oceans. They are usually studied by geophysicists to understand, inter alia, the availability of ore deposits whose electrical conductance is different from that of the surrounding crust. Like ULF (As illustrated in b) below), these bands achieve applications in communication with submarines, and uses very low information rates.
b) 300 Hz - 3 kHz. Ultra Low Frequency (ULF). Water or the earth does not readily consume electromagnetic waves occurring in this range. As such, they might be utilized to communicate among or with submarines and with mines. One drawback is that, with such low frequencies, one can only be in a position to modulate the amplitude sufficiently so they cannot convey much data. This is not a disservice if the stage is needed, as is the situation for systems used for navigation. The wavelengths are long to the point that radio wires may be very long.
d) 30 - 300 kHz. Low Frequency (LF). This band advantageous since waves can be propagated around the Earth, using refraction and reflections within the ionosphere or the earth surface. For this reason, these two wave channels form a waveguide for the radio waves in this range, which can hence be tapped for communication purposes across the oceans and around the world.