Friday, 25 September 2015



The oscilloscope is a remarkably wide range of electronic measuring instruments. It can invisible electrical signal is converted into a visible image, the change process easier for people to study a variety of electrical phenomena. Oscilloscope use a narrow, high-speed electrons from the electron beam hitting phosphor coated screen surface, can produce tiny points of light (which is the traditional analog oscilloscope works.

Under the influence of the measured signal, the electron beam is like the tip of a pen, can depict the change in the instantaneous value of the measured signal curve in the screen surface. Oscilloscope can observe a variety of different signal amplitude versus time waveform graph, you can also use it to test a variety of power, such as voltage, current, frequency, phase, amplitude modulation, and so on.
The instrument used to measure the shape of the wave alternating current or pulsed current, the tube amplifier, sweep oscillator, a cathode ray tube and other components. In addition to observing current waveform, but can also be measured frequency, voltage strength. Where can become electrical effects of periodic physical processes can be observed with an oscilloscope

Analog oscilloscope uses an analog circuit (CRT, which is based on the electron gun) the electron gun to the screen emit electrons, emitted electrons formed by electron beam focusing, and hit the screen. The inner surface of the screen is coated with a fluorescent material, so that the electron beam hit the spot will shine.

Digital oscilloscope is a series of technical data collection, A / D conversion, software programming and other manufactured high-performance oscilloscope. Digital oscilloscope works by analog converter (ADC) to the measured voltage is converted to digital information. Digital oscilloscope captured waveform is a series of samples, and the samples are stored, the storage limit is determined whether the accumulated waveform sample value can be depicted so far, then, digital oscilloscope waveform reconstruction. Digital oscilloscopes can be divided into digital storage oscilloscope (DSO), digital phosphor oscilloscope (DPO) and sampling oscilloscopes.

Friday, 18 September 2015

Very High Frequency VHF

Very High Frequency

VHF Very high frequency (VHF) refers to the 30Mhz to 300MHz band radio waves. Lower than the VHF radio frequency is a high frequency (HF), higher than the VHF radio frequency is UHF (UHF).
Most are used as a VHF radio and television broadcasting, but it is also the aviation and maritime communication channels.

VHF primarily for relatively short-distance transmission, and high-frequency (HF) is different, usually not reflected VHF signal ionosphere, and VHF often affected by environmental factors (such as: topography) on its signal.

VHF omnidirectional range

VHF omnidirectional range (VHF Omni-directional Range, hereinafter referred to as VOR), is a method for aeronautical radio navigation system. Its operating band for the 108.00 MHz -117.95 MHz band is very high, so named. VOR signal transmitted by the transmitter has two: one is fixed phase reference signal; another signal phase angle around the circumference with the beacon is continuously changing, that phase of the signal emitted by each angle is different a. To 360 degrees (pointing to magnetic north) and the reference signal is transmitted in phase (phase difference is 0), and to 180 degrees (pointing to magnetic south pole) transmitted signal with a reference signal phase difference of 180 degrees. VOR receiver on the aircraft according to the phase difference between two signals received can be calculated in the signal itself beacon to which one angle emission. VOR usually rangefinder (DME) with the installation site, in the direction of information supplied to the aircraft, while also providing distance information to aircraft navigation station, the location of such aircraft can be determined only down.

Thursday, 10 September 2015

Ultra High Frequency UHF


 The UHF bandwidth, signal transmitted from the transmitter out of the ground and did not return by the ionosphere to the ground; they are always sent to the universe. Instead, the signal transmitted from the universe always penetrate the ionosphere to reach the ground. Lower frequency users are more familiar with the global "shortwave" UHF spread in not being understood. UHF troposphere can cause bending, pipes, and diffusion, will significantly expand the communication range of the visible range. Aurora, atmospheric scattering, and EME propagation can sometimes be observed, but these models cannot provide reliable communications, they are only interested in amateur radio enthusiasts only. In the upper part of the bandwidth, the wave can focus and calibration by suitably sized dish antenna.

UHF bandwidth can be widely used in satellite communications and broadcasting, cellular telephone and paging systems, as well as third-generation wireless range. Because of the high frequency and wide bandwidths (from low to high have 2.7GHz span), the broadband frequency modulation and spread very practical, channel and sub-band wireless-band super high frequency portion through the International Telecommunication Union (ITU) for distribution.

UHF therapy is the use of the human body without side effects of ultra-high-frequency current, directly on the skin lesions organizations, finely layered and produce complete gasification, an intuitive lesions can be removed. As the instrument precision coupled with the unique operator tactics and operational skills, which greatly reduces the damage to normal tissue, can inhibit scarring UHF mast cells and collagen fibers, and has a bactericidal, veridical, homeostasis anti-inflammatory effect, so to maintain normal tissue wound healing smooth, easy to produce scars.

UHF ultra heat treatment is the lesion tissue by vaporization, lesions in the skin requires what level to what level, so after treatment scab scab off a wound, in the meantime pay attention to the protection of the wound, not wet and a collision. After the scab off the tender skin to prevent ultraviolet radiation, skin care more appropriate diet containing foods rich in vitamins. Dermis lesions recovery needs with few physical scars scar prevention treatment.
As for efficacy, UHF technology overcomes high-frequency electric, laser, freezing, corrosion and other traditional methods of drug recur shortcomings scars, making the treatment of the skin lesion reaches perfection.

Friday, 4 September 2015

CCTV Cameras

CCTV Cameras

Closed Circuit Television (CCTV) an image communication systems. Its signal from the source is transmitted only to pre-arranged point in communication with the source of a particular television. Widely used in a number of different types of monitoring work, education, videoconferencing.

Working principle

CCTV is open television broadcasting stations relative. Broadcast radio and cable broadcasting sub-two, open broadcast television equivalent of radio broadcasting (users get the TV signal from the antenna), it is equivalent to a wired CCTV broadcast (TV mode: TV signal from a satellite transmission side transmitted via cable specify the user). It is the transmission of television signals through wires. It is mainly converts audio and video signals into a radio frequency signal (i.e., a channel), so as to transfer the CCTV system.
CCTV generally refers to television for other than broadcasting, such as television industry, military television, medical TV, underwater television.

Surveillance system

CCTV extremely wide range of applications, and are growing at an unprecedented rate, we can say in all sectors of the national economy, the use of modern technology where all are inseparable from CCTV.

CCTV security technology to prevent the system is an important component is an advanced, highly integrated system of prevention capabilities, it can by remote control cameras and auxiliary equipment (lenses, pan, etc.) is monitored directly Watch place all the circumstances, but also can be linked with other security technology to guard against running anti-theft alarm system and other systems to prevent the ability to be more powerful. Technical requirements CCTV systems are mainly: the camera's resolution, the transmission bandwidth of the system, the video signal to noise ratio, standard TV signals and cameras.

Saturday, 29 August 2015


Photodiode is a way to light according to use, into a current or voltage signal light detector.  Common conventional solar cells are through a large area of the photodiode to produce electricity.
Photodiode with the conventional semiconductor diodes are similar, but the photodiode can be directly exposed in the vicinity of the light source or through a transparent small window, optical fiber package, to allow light to reach the light-sensitive area of this device to detect light signals. Many used to design a photodiode using a PIN diode junction, rather than the general PN junction, to increase the response speed of the device on the signal. Photodiodes are often designed to operate in a reverse bias state.

Infrastructure is typically a photodiode PN junction or a PIN junction. When a photon with sufficient energy shock to the diode, it will excite an electron to produce free electrons and there is a positively charged holes. Such a mechanism is also known as photoconductivity. If the photon absorption occurs in the junction depletion layer, the internal electric field in the region will eliminate the barriers between them, so that the hole can move in the direction of the anode, cathode electrons toward the direction of motion, so the photocurrent arises. The actual dark current and photocurrent is integrated light generated current, and therefore the dark current must be minimized to improve device sensitivity to light.

Photovoltaic mode

When the current bias is 0:00 photodiode in photovoltaic mode, then out of the photodiode is suppressed ends a potential difference accumulated to a certain value. (Solar cell)

Photoconductive mode

When operating in this mode, the photodiode is reverse biased often dramatically reduces the response time, but the noise had to increase the cost. At the same time, the width of the depletion layer is increased, thereby reducing the junction capacitance, also makes it possible to reduce the response time. Reverse bias will cause small amounts of current (saturation current), the current and the photocurrent in the same direction. For specific spectral distribution between the photocurrent and the incident light is linearly proportional to the luminance.

Other operating modes

 Conventional of avalanche photodiode having a structure similar to a photodiode, but requires much higher reverse bias voltage. This will allow the carriers of light generated by the avalanche breakdown substantial increase, resulting in internal gain in the photodiode inside, thereby further improving the response rate of the device.

Thursday, 27 August 2015

Magnetic-core memory

Magnetic-core memory

Magnetic-core memory (English: Magnetic Core Memory) is an early form of computer memory. Magnetic-core memory using memory-magnetic material, its principle is: the magnetic ring (core) with magnetic or non-magnetic properties of the state, to represent the 1 or 0 bit, a long string of 1 or 0 on behalf of the combination of information to be stored.

Magnetic-core memory is a random access memory (Random Access Memory), the computer can assume the role of main memory. Compared to the vacuum tube, the magnetic-core memory power, nor life issues vacuum tube. When the computer into the semiconductor era, there is still a considerable period of time, magnetic-core memory continued role as the main memory. Also, because the magnetic-core memory is non-volatile memory (Non-volatile Memory), one of its features are: Even when the machine or power outage, as long as there are no errors write signal occurs, still can retain its contents.

For magnetic-core memory have an important contribution to the Dr. Wang An, who is also the founder of Wang Laboratories. He invented a reading that is written (write-after-read cycle), to solve one of the important issues on the core body application that will be read at the same time can not erase the memory retains data problems, and later made the relevant patent.
Although the semiconductor memory used today has been a long, but sometimes still use the traditional name, also known as Memory Core, one obvious example is the Core Dump: In the program crashes and abort to save main memory contents up to for debugging purposes.

Sunday, 23 August 2015



Magnet can attract iron and its outer magnetic field is generated objects. Magnet means narrow magnetite ore products, broadly refers to the use of magnets to generate a magnetic field of an object or device. As a magnetic dipole magnet that attracts ferromagnetic materials such as iron, nickel and cobalt and other metals.  Poles are judged by a thread hanging magnet, called the finger pointing to the North Pole or N-pole, pointing to the South Pole as a guide pole or S pole. (If you want to become a big magnet Earth is currently Earth's magnetic north pole is S pole, the geomagnetic South Pole is the N pole.) Magnet is different poles attract, with the exclusion pole. And refers to the Arctic polar attraction guide, guide pole and guide poles repel, repel finger Arctic and Arctic finger.

Permanent magnets and magnet divided into non-permanent magnets. Natural, also known as lodestone permanent magnet, a permanent magnet may be manufactured by hand (the strongest magnets are neodymium magnets). Only non-permanent magnets have magnetic properties under certain conditions, usually in the form of electromagnets to produce, that is, the use of electric current to strengthen its field.

Non-magnetized magnet inside the magnetic molecules (molecular magnets theory) is randomly arranged, arranged in the magnetization process after the magnetic molecules have rules. In this case, N pole and S pole magnetic molecules will be facing in the same direction so that the magnet has a magnetic and become magnets. At the same time, the presence of the opposite poles of the magnetic poles and an equal amount on the same magnet.