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Morse to Mobile Exhibition

This gallery tries to show the process of evolution of communication from the beginning till now. It has pictorial timeline related to invention and entrance of the communication’s tools to people’s life in the world and Iran.

For example you can see there:

Telegraph (Morse)

In sending electric signals over far distances, telegraph messages are written in the form of Morse code. Telegraph has 3 main parts: a transmitter, a receiver and an amplifier. A transmitter consists of a source of electricity (such as a battery) and an electric switch, known as a key for connecting and disconnecting current. The receiver has a single electromagnet. The positive pole of the battery is attached to the transmitter via a wire. By closing the circuit, current flows through the electromagnet, thus creating a magnetic field. The magnetic field causes the receiver’s key to be attracted to the plate beneath. As the key comes into contact with the plate, it makes a sound – a click; therefore, the message received consists of a series of such clicks. The same clicks are produced when the sender transmits the message. Each time the key is depressed onto the plate beneath, thus makes a click. The sender can vary the sound of the click by holding the key down for a shorter or a longer period. The same kind of short and long clicks are then transmitted and picked up by the receiver.

Radios with vacuum-tubes

Radios with vacuum-tubes are fairly old. The amplifier of this type of radio was a lamp (ten times larger than early transistors). In electronics, the vacuum tube is a device that controls electric current through a vacuum in a sealed container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by a filament. The electron cloud has negative charge. By placing a positive metal plate inside the container, electrons will move toward it and so electrons will move from filament toward metal plate. Radio waves are amplitude-modulated, and are of three short wave bands (SW1, SW2, and SW3) and a medium wave band (MW). The frequency signal is picked up by an antenna. For signal reinforcement, several stations have a super-heterodyne receiver. In spite of noise from household and office appliances, the quality of the sound transmitted by AM radio waves is good, due to good design of sound filters.

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