optical communication and networking by gayatri pdf merger

In large versions this pulse is achieved by opening and closing shutters mounted in front of the lamp, either via a manually operated pressure switch or, in later versions, automatically.

The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone, invented in 1880.

When electronic equipment is not employed the receiver is a person visually observing and interpreting a signal, which may be either simple (such as the presence of a beacon fire ) or complex (such as lights using color codes or flashed in a Morse code sequence).

This article provides a basic introduction to different forms of optical communication.

Distress flares are still used by mariners in emergencies, while lighthouses and navigation lights are used to communicate navigation hazards.

Naval ships often use signal lamps and Morse code in a similar way.

Military aircraft landing on an aircraft carrier use a similar system to land correctly on a carrier deck.

The coloured light system communicates the aircrafts height relative to a standard landing glideslope.

As well, airport control towers still use Aldis lamps to transmit instructions to aircraft whose radios have failed.

Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position.

They were far faster than post riders for conveying a message over long distances, but far more expensive and less private than the electrical telegraph lines which would later replace them.

The maximum distance that a pair of semaphore telegraph stations can bridge is limited by geography, weather and the availability of light; thus, in practical use, most optical telegraphs used lines of relay stations to bridge longer distances.

His proposal (which was motivated by military concerns following the Battle of Vienna the preceding year) was not put into practice during his lifetime.

It was used for military and national communications until the 1850s.

For example, Britain and Sweden adopted systems of shuttered panels (in contradiction to the Chappe brothers contention that angled rods are more visible).

This system was considered by many experts in Europe better than Chappes, even in France.

Information is encoded by the position of the flags, objects or arms; it is read when they are in a fixed position.

They are still used during underway replenishment at sea and are acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night.

The transmitter holds one pole in each hand, and extends each arm in one of eight possible directions.

The flags are colored differently based on whether the signals are sent by sea or by land.

At sea, the flags are colored red and yellow (the Oscar flags ), while on land, they are white and blue (the Papa flags ).

Flags are not required, they just make the characters more obvious.

Modern signal lamps are a focused lamp which can produce a pulse of light.

Optical Communication And Networking By Gayatri Pdf Merger