Oscilloscope

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.

Very High Frequency VHF

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.

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.

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.

Photodiode

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.

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.

Magnet

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.

Loudspeaker

Loudspeakers name suggests is the sound amplification, spread farther mean relatively speaker, microphone sound more penetrating.
Loudspeaker according to its size, usage and purpose can be divided into various types, each with their use advantage. Due to the shape and size of portable loudspeakers, speakers’ constraints, general power is only 3--8W. The wireless microphone wired microphone and volume sizes are various different purposes, and smaller size for teachers, tour guides used to hang at the waist, both hands to play more freely, its power is generally also 3W-8W. Bulky for outdoor activities, summer camps, extracurricular lectures and other high traffic areas, the power at 35W --- 95W. Lithium battery according to the type of loudspeaker is made using a classification. It solves the problem of pollution on the environment of traditional batteries, which is used mainly in the mobile phone supply lithium-ion technology to the loudspeaker.

Traditional loudspeakers, through universal, homogeneous competition in recent years, have brought the market price shopping, so that companies are increasingly emphasis on cost rather than quality. Blind pursuit of cost, not only contribute to sound quality cannot be improved, but also makes noise noise increases, to bring a certain degree of physical and mental damage to the user.

Poor sound quality, cannot meet the standard of living has been increasing gradually increasing consumer demand, the market needs to product upgrades. The new "sub-spreader" because the use of crossover broadcast technology to effectively solve the traditional loudspeaker sound rushed, fried, thick, shortcomings. You can enhance the soft and delicate, reduce noise, so sound quality is more stress. The audience does not cause dizziness, irritability, rapid heartbeat, high blood pressure, and entertainment at the same time to feel more pleasure, more physical and mental health. Sub-spreader enables high bass harmony echo, microphone input sound, but also can play a more realistic sound, so seize the audience, enhance the sense of affinity.

Hybrid integrated circuits

Hybrid integrated circuits are then integrated semiconductor integrated circuit external components, or said secondary integration. It is composed of a semiconductor integrated process and thick (thin) film technology combined and integrated circuits made of semiconductor integrated circuits, it is also one of the miniaturization of electronic equipment, the main way to achieve.

Hybrid integrated circuits including the thick-film, hybrid integrated circuits and thin film, thick-film hybrid integrated circuits. Thick-film hybrid integrated circuits is an insulating substrate (typically ceramic) as the substrate of the circuit, and the first conductor network resistance, capacitance and other components using serigraphy, plasma spraying and other craft printed on the substrate surface, then use the WB, TAB , FCB and reflow soldering and other processes, the other components (such as integrated circuits, sensors, other functional elements, etc.) assembled on a ceramic substrate, and then connect the output pin, and finally as a whole package, the formation of a fully functional circuit products. Known as a thick film integrated circuit or directly called thick.

Film hybrid integrated circuit is the use of thin-film vacuum deposition techniques, sputtering, photolithography and other basic process, the electronic components of the circuit in the form of film products in the production of circuits formed on an insulating substrate.

Programmable DC Electronic Load

Programmable DC Electronic Load is the principle of the flux guide or the control of the power MOSFET transistors (duty ratio of the size of the volume), the power dissipated by the power consumption of the power tube apparatus which can accurately detect the load voltage, load current precise adjustment, while analog load short-circuit, an analog resistive and inductive load is capacitive, capacitive load current rise time. Debugging detect general switching power supply is indispensable.

Programmable DC electronic load can simulate real-world loads (appliances). It has a constant current, constant resistance, constant voltage and constant power capabilities, as well as short circuit, over current, dynamic, etc., it should be said that all power manufacturers will be useful, but also must have. Electronic load into DC electronic load and AC electronic load, electronic load due to the application surface problem, this paper introduces the DC electronic loads.

1. Voltage, current and power of choice

According to the output characteristics of the device under test to select electronic load: voltage, current, power and accuracy of the testing requirements. Programmable DC Electronic Load Module can only work when tested alone or parallel operation, the series for the module is very dangerous. So ideal state is that all requirements are within the range single group, followed by multiple modules connected in parallel to achieve the selection. That is, when the voltage of the selected module must meet the test requirements. Individual modules or the full sum of the current and power box is installed to meet the testing requirements.

2. Accuracy and resolution choices

Accuracy and resolution is an important parameter index electronic load. Meaning accuracy of different representations of programmable DC electronic load.

Capacitors

Capacitor referred capacitors; it is also a major element of the electronic circuit components. It can store electrical energy, with the charge, discharge and through the exchange, DC-blocking properties. In a sense, a bit like a capacitor battery. Although both work in very different ways, but they can store energy.

Battery has two electrodes inside the battery, so that a chemical reaction to produce electron electrode, the other electrode of the electron absorption. The capacitor will have a much simpler, it does not produce electron - it just to store electrons. It is one of the indispensable basic elements of the extensive use of various types of electronic equipment. Various capacitors in the circuit can play different roles, such as coupling and DC blocking, bypass, rectifier filter, high-frequency filter, tuning, storage and division and so on. The capacitor should be selected according to the circuit voltage, frequency, waveform, AC and DC components of temperature and humidity conditions.
Capacitor, typically referred to its ability to hold a charge capacitance, denoted by the letter C.   Capacitors, by definition, is 'loaded container electricity', it is a device receiving the charge. English name: capacitor. Capacitor is one of a large number of electronic components used in electronic equipment; it is widely used in the circuit compartment straight cross-connection, coupling, bypass, filtering, tuning circuits, energy conversion and control.

The capacitance of the capacitor is different. Capacitance basic physical quantities, the symbol C, the unit is F (farad).

General formula C = Q / U parallel plate capacitor special formula: electric field strength between the plates E = U / d, the capacitor capacitance of the formula C = εS / 4πkd.

Amplitude modulation

Amplitude modulation (AM) also referred to as amplitude, by varying the amplitude of the output signal, to achieve the purpose of transmitting information. General changes in the amplitude modulation of the high-frequency end of the output signal and the original signal into a certain function, demodulation end demodulates and outputs the original signal.

In fact, a function is generally proportional relationship. The greatest benefit of this modulation is the modulation and demodulation is very simple, just a diode and a capacitor can, of course, the biggest drawback is the relatively large distortion, while more sensitive to interference, relatively speaking, is a relatively old technology. But technology does not mean that the old applications are not widespread, there are still many areas of application, such as a radio (AM radio) and Aeronautical Radio, Especially in the field of aviation radio, the traveling speed of the aircraft very quickly, quicker fighter, for FM, the Doppler effect is too big, it will affect communications, and AM is not affected by the Doppler effect, it can not be replaced. At the same time there are some improvements AM techniques, such as single sideband modulation (also known as single sideband), residual sideband modulation (Vestigial Side Band, VSB), and amplitude modulation multiple variants such as the current amplitude is widely used in a mobile communication digital modulation.

Dipole antenna

Dipole antenna used to transmit and receive signals of fixed frequency. Although the usual measurements are used in wideband antenna, but the venue and the measurement antenna attenuation coefficients are required to use a dipole antenna. Dipole antenna in the frequency range 30MHz ~ 4GHz. Which is a set of precise VHAP and UHAP dipole antenna is especially suitable for measuring site attenuation and antenna factor. Meanwhile, the antenna for the Japanese VCCI standards organizations designated only dedicated antenna anechoic chambers and open-field site attenuation measurement and the like. The antenna is used by many laboratories, as antenna standard laboratories.

Vertical antenna is actually a dipole antenna. Dipole antenna consists of two conductors, each 1/4 wavelength, i.e., the total length of a half wavelength of the antenna. So dipole antenna, also called half-wave dipole. The transducer can be a dipole antenna horizontal position, vertical position may be. Its pattern to the feeding point of symmetry. Feed point in the center of the half-wave vibrator. Feed point impedance is purely resistive, approximate 75Ω (approximately 73Ω). If the two 1/4 wavelength resonator extended and then folded back to the center, and joined together, then it became a folded dipole antenna, referred to as folded vibrator.

Folded dipole antenna impedance is purely resistive approximate 300Ω (about 290Ω), shows a high input impedance, high impedance transmission antenna feeder parallel constitute use in many occasions. The dipole antenna straight up, perpendicular to the ground, then a vertical antenna. If the "remove" the lower part of the 1 / 4λ oscillator, the asymmetrically vertical antenna. Common vertical antenna are asymmetric antenna, isotropic in the horizontal direction.
A special.This antenna has a special name called Marconi antenna. R7000 receiver and other antenna configurations belong to this antenna.

Battery

Battery, defined in a narrow sense is itself generally stored chemical energy into electrical energy device, broadly defined as pre-stored energy from the device into external power available. So, like solar conversion without storage function only means not a battery. Other names have batteries, batteries, and Chinese have storage tanks and bottles intended effect.
Historical battery can be traced back two thousand years ago in ancient Iraq era. In the capital Baghdad found unglazed clay pots. It is a copper and iron battery.
Type of Batteries

Chemical batteries, electrochemical cell means by an oxidation-reduction reaction, the positive electrode, a negative electrode active material of chemical energy, into electrical energy for a class of devices. Common redox reaction with different oxidation and reduction reactions that are carried out separately, the oxidation of the negative electrode, the reduction in the positive electrode, and the electron gains and losses is carried out by an external circuit, thus forming a current.

Dry and liquid batteries distinguish battery is limited to that period of early development. The first battery of a glass container filled with an electrolyte and two electrodes. Later we introduced to paste electrolyte-based batteries, also known as dry batteries.

Disposable batteries (Primary Battery), commonly known as "disposable" cell, because after their power runs out, can not be recharged using only discarded. Common disposable batteries include:
Manganese battery - voltage of about 1.5V, the battery capacity is low, the battery can output low, almost alkaline manganese batteries are replaced, except after long-term storage is not leaking harmful corrosive liquids, so still in use in low electricity requires long-term use of devices simultaneously, such as clock, infrared remote control and so on.
Alkaline manganese battery - voltage of about 1.5V, battery capacity and output of the battery than the zinc-manganese batteries is high, but less than nickel-metal hydride battery, after long-term storage of hazardous leaking corrosive liquids.

Other disposable batteries include zinc batteries, zinc-air battery, zinc-mercury batteries, mercury batteries, battery and magnesium hydroxide, manganese batteries.
Rechargeable batteries, also known as the secondary battery (Secondary battery), batteries. Rechargeable battery according to different production materials and workmanship, the advantage can be reused many times after it is charged, they can be full charged and discharged more than two times or even up to 2500, the rechargeable battery output current (load force) than large part disposable batteries is high. Common types are:

Lead-acid battery - voltage of about 12V, low capacity, but can output more power, battery, often used in automobiles for starting the engine to use, or for uninterruptible power system (UPS), radios, communications machine.

Avalanche diode

Avalanche diode negative resistance is generated solid microwave devices using semiconductor structure carrier impact ionization and the transit time of two physical effects.

PN junction one-way conductivity, resistivity is small, a large reverse resistance.

When the reverse voltage is increased to a certain value, reverse current suddenly increases. It is the reverse electrical breakdown. It points avalanche and Zener breakdown.

Avalanche breakdown PN junction reverse voltage is increased to a value, like an avalanche multiplication of carriers, as far and fast increase.

Take advantage of this feature is to make the crystal diode avalanche diode
Major domestic manufacturers have Haiou light OTRON brand.

Avalanche breakdown in the electric field, the carrier energy increases constantly collide with atoms in the crystal, so that a covalent bond is formed in the electron excitation of free electron - hole pairs. New carriers generated by the collision and free electron - hole pairs, which is a multiplier effect. 1 Health 2,2 Alive 4, the same increase as the avalanche of carriers.

Zener breakdown is completely different, at high reverse voltage, there is a strong electric field PN junction, which can directly destroy covalently bound electrons will be separated to form an electron - hole pair formed a large reverse current. Zener breakdown electric field strength required great!

Only in impurity concentration particularly large PN junction to do the job.
It is in the applied voltage can produce high-frequency oscillation of transistors. High-frequency oscillations generated works: the use of avalanche breakdown of the crystal injected carriers, because the wafer carrier transit will take some time, so its current lags the voltage, It is often used in the field of microwave oscillation circuit.

Ampere

Ampere, referred to security, is the International System of Units in the current strength of the unit, the symbol is A. at the same time it is also one of the seven basic units of the International System of Units . Ampere is the French mathematician and physicist Andre - Marie Ampere named, in honor of his contribution in terms of classical electromagnetism.

The actual situation, ampere is a unit of time cross-sectional measure the amount of charge through a conductor. Within one second by the cross section of 1 coulomb charge (6.241 × 1018 electrons in the charge), the current size of 1 amp
small current can be expressed in mA, microamps and other units.

1 Amp (A) = 1000  (mA)

1 milliamperes (mA) = 1000 microamps (μA)

Ampere force law of proof in a parallel existence of two straight power-attraction or repulsion between wires. This force is used to formally defined amps:
Vacuum, in two parallel infinitely long straight conductor cross-section can be ignored, and the distance of one meter. Through the same size, the same constant current direction in the two wires, when the wire is attractive per meter by 2 × 10-7 Newton, the two wires of the current of one ampere.

Ampere was originally defined as a centimeter - tenth - second current unit abampere - grams. Its size is so determined to ensure the international system of units derived from other units ampere value obtained is appropriate.

"International ampere" is an older unit of electric current, defined as the silver nitrate solution to precipitate the current 0.001118000 grams of silver per second. After a more accurate measure found that the current is 0.99985 A.
This unit Ampere and Watt balance and Ohm's law in the unit volts, ohms linked.

Sound System measurements

First, the human ear any subjective feelings are "absolutely" objective measurements may be used to represent data, otherwise all the knowledge of cognitive psychology and the psychology of perception on all the deceptive; please do not doubt, even religion and love so complex ideas can be objectively measured, under relatively sound sense of hearing is so simple! But we may not know how the existing capacity measure, or someone else had found and we did not know.
The second, but not a simple physical phenomenon "objective measurement data," mostly psychological phenomenon. This is why the measurement data clearly incorrect, but the listener can feel good to hear, because of the psychological feelings and physical stimulation is not a linear relationship.

To take a simple example: Please find a white paper, starting from the middle of a half will completely blacked out. ok, then you will say, external physical stimuli is not just black and white two properties, what else? It really wrong ...... physiological phenomenon of human vision, through the so-called ZERO CROSSING conversion, you'll find close to the middle boundary, white, more white, black and more black; this is certainly no humans there will be a normal physiological and psychological phenomenon.

Therefore, if we only care about the qualitative and quantitative external physical stimuli, will never forgive restricted to physical stimuli only black and white, do not know the human psychological phenomenon is real, "especially from black to white and black to white and then to special"; Just watch see "only physical stimulation from outside" view of human senses, it is not limited and lost a lot of rich message.

Many people see here say: Behold! Objective measurements useless ...... The more outrageous mistake. Because, objectively measured "absolutely" helpful; you then can not see how there is absolutely subjective, "especially from black to white and black to white and then to special" feeling in a black paper; this feeling, though not on the physical stimulation, but it is absolutely linked to a specific physical stimulus. So the first point I would emphasize: "All the subjective feeling" absolutely "objective measurement data can be used to represent" the only question is: even if we find the correct physical measurement data, how do we "explain" to get corresponding psychological feelings.

Because of the psychological feelings and physical stimulation is not a linear relationship, so for the "physical measurement data" "correct interpretation" even more important than the "right measure." Any physical data are not directly correspond to any sense of hearing, all we need to "correct interpretation"; and this explanation is necessary is an objective, because everyone should all have similar physiological and psychological phenomenon. So, at first glance subjective psychological feelings, still reflects a variety of objective material or social factors, it will never be cool enough to hear so simple.

Thirdly, I hereby personally think: with objective physical measurement is the "basic", is "starting from scratch", is "self-growth start." Even if I did not play a sound people listen to music, I listen to music when I found into a bottleneck and intend to re-start, what to do? Return to the starting point, increasing the "voice" of the objective of the physical message from the start; so he began to desperately play sound.

Cassegrain antenna

Cassegrain antenna is another commonly used in microwave communication antennas, which evolved from a parabola. Cassegrain antenna consists of three parts, namely the main reflector, sub-reflector and the radiation source. In which a rotating parabolic main reflector, sub-reflector surface of the rotational hyperboloid. Structurally, the focus of a hyperbolic paraboloid focus coincides hyperboloid focal axis coincides with the axis paraboloid focus, and the focus of the radiation source is located on another double curved, as shown below. It was a reflection of the electromagnetic radiation emitted subreflector carried out, the electromagnetic wave reflection to the main reflector, and then after the main reflector reflected plane wave beam obtain directions to achieve directional transmission. Cassegrain antenna works as follows.

When the radiator located hyperboloid of revolution real focal point F1, the rays emitted from F1 after the reflected rays hyperboloid, the equivalent of the virtual focus hyperboloid emitted directly out of the rays. So as long as the focus of the hyperboloid virtual focus coincides with the paraboloid, the sub-reflecting surface can be the main ray reflecting surface is parabolic reflector in a plane wave radiated.

Cassegrain antenna with respect to a parabolic antenna is concerned, it will feed the radiation pattern from the feedforward parabolic manner changed after the feeding mode, which makes the structure of the antenna is more compact, making it more convenient. Also Cassegrain antenna is equivalent to a parabolic antenna with a long focal length, and this can be a long focal length to the distance from the antenna from the focal point of each aperture is nearly constant, thus space radiation attenuation effect on the feeder to be smaller so Cassegrain antenna efficiency is higher than the standard parabolic antenna.

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.