Directional antenna

Directional antenna refers to the transmitting and receiving electromagnetic waves is particularly strong on one or a few specific direction, while transmitting and receiving electromagnetic waves is zero or a minimum of an antenna in the other direction. Directional transmitting antenna is intended to increase the effective radiated power utilization, increase confidentiality; the main purpose of the use of directional receiving antenna to increase signal strength is enhanced anti-jamming capability.

Directional antenna used to cover a long street, and has the following advantages:

1, has a large forward gain

2, the signal, when the cell behind the cell it would potentially interfere with this feature is useful to inhibit later.

Also worth mentioning is the directional antenna can improve indoor coverage within the micro-cellular coverage in some buildings.
Directional antenna in the horizontal direction in Fig showed a range of angles of radiation, which is usually referred to directional. Like with omnidirectional antenna, beam width is smaller, the greater the gain. Directional antenna in a communication system generally used in communication distance, small-coverage, high target density, high frequency utilization environment.

We may also like this to think about the relationship between omnidirectional antennas and directional antennas: All will transmit a signal to the antenna in all directions around, you can receive the signals, directional antenna like antenna mask after a bowl-shaped reflective surface, signals can only be transmitted to the front, towards the back of the signal is blocked by the reflective surface and is reflected to the front, reinforced front signal strength.

Ohmmeter

Ohm meter (ohmmeter), also known as resistance table, is a specialized instrument for measuring electrical resistance. Electromechanical components impede the flow of current nature, called the resistance in ohms. Milliohm meter special measuring small resistance; and megohms meter, also known as Megaohmmeter, or high table, the special measure very great resistance.

Ohmmeter original design, with a small battery voltage is applied to the resistor, and, with a modified galvanometer (galvanometer) to measure the current flowing through the resistor. Galvanometer scale marked change in ohms. Due to the constant voltage applied to the battery to ensure that the current will be inversely proportional to the resistance. So, know the current, you can get resistance.

As shown right ohmmeter scale representation from zero to infinity. When in contact with the two probes, the resistance is zero; when separated, the resistance is infinite. The majority of the number of domains between the two numbers to a logarithmic scale mode of expression. So, assuming the battery of emf 6 \ volt \, \!, You want to set current 4 \ mA \, \!, The internal resistance must be adjusted to 1.5 \ k \ Omega \, \!. When two probe together, the total resistance is 1.5 \ k \ Omega \, \!, Current is 4 \ mA \, \!, Ohm meter display shows the resistance to needle 0 \ k \ Omega \, \! .

When displaying the needle in the middle of zero and infinity, the current is 2 \ mA \, \!. So, the total resistance is 3 \ k \ Omega \, \!, The measured resistance is 1.5 \ k \ Omega \, \!.
When displaying the needle in the middle between zero and 1.5 \ k \ Omega \, \! When current is 3 \ mA \, \!. So, the total resistance is 2 \ k \ Omega \, \!, The measured resistance is 500 \ \ Omega \, \!.
When the display needle 1.5 \ k \ Omega \, \! In the middle with the infinite, the current is 1 \ mA \, \!. So, the total resistance is 6 \ k \ Omega \, \!, The measured resistance is 4.5 \ k \ Omega \, \!.

This ohmmeter has an important drawback is that it requires a very stable battery voltage. After a period of use, the voltage will gradually decrease. This will make ohm meter lose accuracy. When in contact with the two probes, the display no longer needle will point 0 \ k \ Omega \, \!, And will point to the growing resistance.

Diode

Diode is a kind of asymmetrical double electrode conductance electronic components. Ideal diode in the forward conductive between its two electrodes (anode and cathode) have infinitely small resistance, and the reverse when there are infinite resistance, ie, the current is allowed to flow from a single direction only through the diode.

Diode having an anode and a cathode two terminals, current can only flow to a single direction. That is, the cathode current may flow from the anode, and not from the cathode to the anode. To diode possess one-way nature of such applications, often called "rectification" function. In the vacuum tube, with a voltage applied between the electrodes so that hot electrons can reach the anode from the cathode, thus rectifying effect. The alternating current into direct current, comprising a radio receiver for a radio signal modulation, are accomplished by the rectifier.

Reverse circulation because of its forward blocking characteristics, diode can be thought of as an electronic version of a check valve. However, in practice, diodes and do not exhibit such a perfect switch resistance, but showing a more complex non-linear electrical characteristics - which are determined by the specific type of diode technology. In general, only in the forward reaches the threshold voltage, the diode will start to work (this state is called forward bias) A change in the voltage drop across the diode is forward biased only to do with current, and is a function of temperature. Therefore, this feature can be used to the temperature sensor or reference voltage.
Semiconductor diode non-linear current - voltage characteristics, thereby forming an impurity may be different depending on the selected semiconductor material and a semiconductor doped with different impurities to alter.

Diode characteristics after the change in the use of switches used in addition to the way, there are many other features, such as: used to adjust the voltage (Zener diode), thereby limiting the high-voltage protection circuit (APD), radio tuner (varactor), generating a radio frequency oscillation (tunnel diode, Gunn diode, IMPATT diode) and generate light (light emitting diode).

Semiconductor diode, there is the use of P-type and N-type joints PN junction of two semiconductor effect, but also the type of Schottky rectifying action to achieve the effect produced by the use of a metal-semiconductor bonding. If the PN junction type diode, the P-type anode side is, N-type side is a cathode.

Power Supply

Power Supply  usually it refers to the source of electricity. It could be a system or device for supplying electric power, or other device capable of providing energy to the load output of the power supply.

Power supply to other forms of energy into electrical energy device called a power supply.
Generator can convert mechanical energy into electrical energy, batteries can convert chemical energy into electrical energy generator battery itself is not charged, its positive and negative charges respectively poles, positive and negative charge generated by the voltage (current voltage is under the effect of the charge directional movement formed), there would have been in charge of the conductor to produce current only voltage can, when the battery is connected to the conductor to generate electricity poles and the release of positive and negative charge out, when the charge is dissipated, also do you charge flow (pressure) disappeared. batteries and other known power supply. Through the transformer and rectifier, the alternating current into direct current power supply device called a rectifier power. To provide an electronic device called a signal source. Transistor can be amplified signal sent, again amplified signal is transmitted to the back of the circuit to go. Transistor on the back of the circuit can also be seen as a signal source. Rectifier power supply, sometimes called the power supply source.

LED and LCD TV

LED-backlit LCD TV is the use of light-emitting diodes (LED) as a liquid crystal display backlight TV. this does not mean that television use light-emitting diodes for image display With the light-emitting diode TVs increasingly competitive market, coupled with the light emitting diode applications matures, various TV manufacturers have actively into the light-emitting diode-backlit LCD TV, an attempt at a home television on the occasion of regime change can come out on top.

Types of light-emitting diode backlight technology;

LED back-light technology can be divided into direct type (direct back-lit or full LED array back-lit) and side-illuminated (edge LED back-lit) are two, and light-emitting diodes which are used in direct-divided into white light diode and red, green and blue light-emitting diode two kinds.

1-Direct type light-emitting diode backlight technology;

Direct type LED back-light technology is the more pieces of light-emitting diodes arranged in an array, placed behind the LCD diffuser and directly illuminated LCD. Thus, the direct type can comply with different parts of the screen brightness changes quickly fine-tune the brightness of the light-emitting diode, greatly improve the level of dynamic contrast ratio to the plasma display. The disadvantage is the need to use a large number of light-emitting diodes, and higher prices.
Had a direct type LED back-light use white LED, also used red, green and blue color LEDs (RGB LED) using RGB LED can have a wider spectrum of light, that have a wider color field.

2-Side-light emitting diode backlight technology;

Side-light emitting diode backlight technology is to white light emitting diodes on four sides of the LCD, LCD size with the LCD after a close reflective film, light emitting diodes LCD with photos from the gap between the reflective film inside, reflective film on a specially designed micro LED lighting pattern can come back after the LCD according to the light for 90 ° reflection. These reflective sheet was fine in the case without astigmatism sheet also enables the average light-emitting diode light distribution to shine LCD back.

Conventional side-illuminated light-emitting diode backlight brightness compliance can not quickly adjust brightness change different parts of the screen, but recent changes in vendor compliance screen success with the side illuminated LED technology limited quickly adjust brightness.

LED or light emitting diode

LED is a light emitting diode (Light Emitting Diode, LED) for short, also known as light-emitting diodes, the semiconductor component is generally used as the indicator, a display panel, which not only can efficiently direct contact Mitutoyo photovoltaic electrical energy into light energy, while the operating voltage is low (some only a little over volts).

And have the most up to tens of thousands of hours to 100,000 hours of life, but have not as conventional bulbs fragile, and the advantages of energy saving.

It is a semiconductor diode that can put energy into light energy; often abbreviated is an LED. Like ordinary diode emitting diode is a PN junction composed, also with unidirectional conductivity. When coupled to the light emitting diode forward voltage, injected into the holes from the P region and the N zone area by the N electrons injected into the P region, near the PN junction within a few microns were empty and Electronics and P region of the N region Point complex, resulting in the spontaneous emission of fluorescence. Energy states of electrons and holes which are different in different semiconductor materials. When an electron and hole recombination energy released somewhat different, more energy released, the shorter the wavelength of light is emitted. Commonly used hair red, green or yellow light diode.

Liquid crystal display LCD

Liquid Crystal Display, abbreviations: LCD flat thin display device, by a number of color or monochrome pixel composition, placed in front of the light source or reflector side. Low-power liquid crystal display, so much favored by engineers, for battery of electronic equipment.

Each pixel of the liquid crystal display consists of the following parts: two layers of liquid crystal molecules suspended in a transparent electrode (indium tin oxide) between a columns outside on both sides with two mutually perpendicular polarization directions of the polarizing filters. If there is no liquid crystal between the electrodes, wherein the light through a polarizing filter whose polarization direction of the sheet, and the second polarizer perfectly vertical, and therefore is completely blocked. However, if the polarization direction of light through a polarizing filter sheet is rotating LCD, then it can be filtered through another polarizing sheet. Liquid crystal rotates the polarization direction of the light can be controlled by an electrostatic field, in order to achieve light control.

Liquid crystal molecules are easily affected by the induced charge arising from the applied electric field. A small amount of electric charge is applied to the transparent electrode of each pixel or sub-pixel to produce an electrostatic field, the liquid crystal molecules are induced by the electrostatic field induced charge and static torque, leaving the liquid crystal molecules are originally aligned to produce a rotating change, so also changed by rotating the amplitude of light. Changing the certain angle, it is possible through the polarization filters.

Before the charge applied to the transparent electrodes, the liquid crystal molecules are arranged to determine the alignment of the electrode surface, chemical surface electrode may be used as seed crystals. In the most common TN liquid crystal, the liquid crystal vertically aligned upper and lower electrodes. Liquid crystal molecules are spirally arranged, through a polarization filters rotated polarization direction of the light after passing through the LC panel, thereby through another polarizer. In this process, a small portion of the light blocked by the polarizer from the outside appears to be gray. After the charge is applied to the transparent electrodes, the liquid crystal molecules almost completely along the field direction are arranged in parallel, and therefore the direction of polarization of light through a polarizing filter sheet is not rotating, and therefore the light is completely blocked.