maritime communication

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High frequency radio (commonly known as short waveradio) is a means of communication in which a radio wavesignal is transmitted from one point to the ionosphere,where it is reflected back down to another point onearth.

The term "high frequency" refers to the number of radiowaves transmitted per second, and simply serves todistinguish this type of system from those whichtransmit at higher or lower frequencies.

Consists of three basic components, thetransmitter/receiver unit (commonly called thetransceiver), the antenna and the power source.

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For many years, HF radio was the major form ofcommunication in the Arctic and was considered

appropriate for the North because it was a suitableand economic form of long distance communication.

Also, HF radio does not permit privacy of

conversation. Anyone within range and access to thesame frequency may listen to the communication.

HF can be used for communication over great

distances and between points separated bygeographic barriers, such as mountains.

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Upper part of atmosphere. About 50-500 kmabove earth’s surface. 

Radiation from the sun produce free electron (-

ve charged). The molecules that lose electron (+ve charged).

The free electron and ions cause HF radiationthat moving upward to bend toward the effect.

The higher the amount of free electron, moreHF radiation is bent toward the surface.

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Ground Wave -Emitted waves follow the circumference

of the Earth’s surface. 

-Use for :* VLF (submarine b/cast)* LF* MF (radio beacon, coastal comm)* HF (provide gap-less cover for

tactical circuit

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Direct Wave -Emitted waves travel in straight line.

-Used for :

* VHF/UHF : short range ship-ship,port comm.

* EHF/SHF : satellite comm.

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Sky wave 

-Emitted waves leaves the transmittingaerial at a greater angle than horizontaland travel upwards until encountering the

ionsphere and back to the Earth.-Used for :

* HF : long distance comm,broadcast, ship-shore, fixservices.

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Long range : the lower the frequency, thelonger the wavelength, the further signal canpenetrate thruogh solid object or a liquid.

Minimal insfrastructure requirement.

Full mobility.

Introperability.

Low cost.

Security of communication.

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Propagation has strong diurnal

variation/effect Easy target for detection.

Transmitting antenna must belarge.

Limited information can be sent.

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Reduce the power and used it wisely

depend on distance. Development of electronic device.

Study of computer and IT.

Set up the automatic electronicoperator that capable for skywave.

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