Information sent may include images, sounds, or specific information. On the technical implementation, this information is converted into a signal. This will facilitate the process of signal transmission from transmitter to receiver. This whole process requires a transmission medium, called a transmission line, in sending the information to be accepted at the destination.
In a telecommunications system there are 3 important parts which are interconnected ie, the sender (transmitter), transmission media (transmission line) to the recipient (receiver). Information sent by the transmitter signal can be pictures, sounds, or data signal / message. This information is channeled through the transmission (channel) medium can be either with a cable (wire) or wirelessly (wireless). The information transmitted in the channel and subsequently accepted by the recipient (receiver). In further developments, the medium used for the latest optical fiber, wireless media can be used in space satellites, light and even wi-fi. Users (subscribers), many who use media with the transmission of light.
Light is considered as an alternative transmission line are eligible, because light can distribute information quickly inserted into the transmitter until the lights as the right media with the speed? 3108 m / s. Light is energy berkuanta. Light has a charge in it, fill known as photons. These photons interact with one another to produce a form of energy (Rustam, 2005). Because light is energy, he grouped a certain classification (spketrum) characteristics that underlie some forms of energy. In light of this division are known as Spectrum Light. These spectra are grouped according to certain akrakteristik in different light.
In the light has a wavelength (350nm-680nm) can be used in several applications in the field of science. Some of them, the use of LASER beams to detect diseases that will be used in a lighting show, then began using optical fiber as a medium for the transmission distance by changing the role of telecommunications cable. Emiited Light Diode (LED) can be used in trasnmisi media, telecommunications context. This media has a relatively small wavelength (± 700 nm), but this medium has an intensity of energy (± 20 mW / A). To note that, the characteristics of LED.
Dioe emitted light (LED)
light emitted diode (LED) is a tool that applies a monochromatic light. How it works by altering the electrons into photons. Electrons are fed by voltage source (forward bias) will experience an electromagnetic field to generate electrical current. electric current is then going to "live" right-diode (LED) until the LED will emit a photon energy in the form of LED lights (Lizuka, 2008). Next image LED working principle.
In LEDs, can be viewed as a crystal. These crystals consist of a hole (holes) and electrons (ions), electrons will fill each empty hole in recombination caused by the delivery of electrical current from the source voltage (forward bias). When the electrons recombine with holes already, regardless of cause electron binding energy. This recombination resulted regardless of electron energy. The energy released is used to emit photons (radiaktif recombination), the other part is used to heat the crystal particles (non-radiaktif recombination). Emitted light is an LED light.
Some characteristics of Light Emitting Diode (LED), among others:
* The color (wavelength) is determined by the band-gap
* Light intensity is comparable with existing results
* Non-linearity appears at low and high flow
Self-heating (self heating) decrease in efficiency at high currents.
Signals can not move themselves. For that we need tools to signal to move, give the tool is intended to simplify the signal before moving from one source to another. Tools (tools) that typically use modulation techniques.
Modulation technique can be interpreted in the telecommunications with the laying of a signal to the original signal. Signals from here can be translated as the original signal that carries information messages (data), also described as a data signal. combination signal is then known as signal modulation, while the data signal is modulated signal is known. Pemodualsi frequency signals must have a value higher than the initial signal, it is because if pemodualsi signal has no frequencies higher then modualsi produced is not perfect. In modulation, a technique widely used in the transmission of data signals to a distance or near, the use of techniques based on signal processing will kemudahah in dimoulasi by the modulation and the process can be observed directly. In communication systems there are some great benefits that come from modulation techniques include:
1. Allows sending a weak signal with a "free ride" a wave of high-powered carrier.
2. Can reduce the size of the antenna for transmitting signals through a carrier wave which has a high frequency (short?).
3. Allows setting and allocation of separate frequencies for the distribution of multiple signals simultaneously through the same media.
4. Allows the frequency shift signal to the frequency area is more easily processed by the equipment available.
Carrier wave signals from superimposed signals. Putting on the wave, because the wave can move over long distances. For example, light waves. If the intensity of the light source is converted into a place to eat widely accepted. In signal transmission, no interference (noise), this disorder which then affect the effectiveness of the LED. At the light, the relative interference from external factors, such as outside light. Transmission distance can be a factor of disturbance, light waves, changes in light will produce light intensity can be reduced.
The reconstruction technique is to re-demodulate the signal modulated into a form. This process is the reverse of the modulation technique. In demodulate modulated signal will be received by the receiver, called a detector. Detectors are then responsible for detecting the transmitted signal (modulated) to the next in frequency. Demodulation process carried out must be the same modulation is used, such as if the signal is modulated signal with the FM technique, demodulation using FM demodulation. After the demodulation process performed, then the information is superimposed by a carrier wave signal will be received.
The use of detectors, which use light waves to detect the presence of the light wave signal transmitted by the transmitter (transmitter), a detector which is used in light wave is LDR and PD (photo diode). Both detector suitable for use in mechanics bersifar demodulation. Photodiode used in this study, because the detector is more sensitive to light sources that came to him and with a relatively good conductor temperature, so the use of diodes is considered suitable. The working principle of this diode is the reverse of how the LED, when light source captured by the photodiode, the light source in the form of light photons converted into electrons which then will become an electric current due to electromagnetic. So the number of modulated signal will be read in units of volts time domain.