Comparison of twisted pair and coaxial cable

锛?鍚岃酱浼犺緭绾挎槸涓?浼樿川瀹藉甫灞忚斀浼犺緭绾?br />
[Quality]: transmission attenuation.

[Broadband]: Now the level of our products have achieved 0 ~ 20Gz; twisted pair coaxial transmission bandwidth is about 1 / 10;

[灞忚斀]锛氬畠鎶婁紶杈撲俊鍙风殑鐢电鍦哄叏閮ㄩ檺鍒跺湪灞忚斀灞傚唴閮紝涓嶅悜澶栬緪灏勶紝鏍规嵁鏀跺彂鍙?鍘熺悊锛屽鐣岀數纾佸満涔熶笉鑳界┛杩囧睆钄藉眰杩涘叆鍐呴儴銆?br />
The principle of coaxial interference produced is another matter, twisted pair is different, its signal transmission electromagnetic field theory is distributed in infinite space. Reversible under the principle of sending and receiving, the external electromagnetic field can also go directly to twisted pair. Twisted pair can not prevent external electromagnetic field to enter, but with a helical twist of the way, so that two lines of the received signal, "exactly the same as far as possible", and a balanced differential signal processing technology, the same as that of "common-mode signal "restrain out. The key here is the twisted pair of "balance" feature, "balance" when there are differences, interference can take advantage of the external object will also affect the balance. Project on "balance" is relative, not absolute, the circuit's "common mode rejection" has a range of performance. These two practical problems, determine the twisted pair of anti-interference ability is limited, the integration of network cabling in the Rules strong interference case, you must use shielded twisted pair, is the truth.

2. Coaxial and twisted pair transmission characteristics is provided by the national standard, can not change. Such as video signals on top band for the 6M, the 2000 meters transmission distance, SYWV-75-5 cable attenuation of 40db, the voltage decay 100 times, 1Vp-p video signal attenuation of 6M to 10mv, or 80db microvolts, in this level video resume, you can ensure high SNR. Experience with the cable system design engineers, is very clear; for unshielded twisted pair, 2km of 6M attenuation of 92db, attenuation of nearly 4 times higher than 75-5 coaxial large 52db (400 times);

3. Twisted pair 2km, 1Vp-p signal attenuation to 25 micro-volts, that level is 28db microvolts, and the circuit has the noise level can be close, only the end of the compensation signal to noise ratio will seriously deteriorate the way out can only enhance the front-end level.杩欏氨鏄洰鍓嶅弻缁炵嚎浼犺緭蹇呴』閲囩敤鐨勨?鍓嶆帹鍚庢媺鈥濇妧鏈柟妗堬紝瑕佹眰鍓嶅悗璁惧鐨勮ˉ鍋挎彁鍗囨?鑳藉姏蹇呴』澶т簬92db,瀹為檯搴旇鍋氬埌100db銆?Now I only see a manufacturer provides a 60db capacity building of the data, do not know is that the frequency data. Also to note, front-end large-signal amplification to enhance the inherent noise generated by the circuit itself, than the end of the small-signal circuit intrinsic noise generated by much larger, faster deterioration of the system signal to noise ratio, it was suggested that twisted pair transmission equipment relay relay series can do a lot (a lot more than the coaxial), which is entirely ignorant of the imagination, theory and practice are not justified;

Conclusion: Comparing the coaxial and twisted pair transmission system, two points must be seized: one more difference between transmission characteristics of two lines, the second is to look at the performance level and transmission equipment.







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Open-source framework for thinking about [2]

Although we have stressed the whole is greater than the sum of the individual, but how a single "individual" right to play a greater effect of the combination into the "whole" is not easy. Because these single framework developed by different teams, the framework and the framework of the impedance between the natural, between this framework and the framework of the "generation gap" requires additional configuration and coding to close.

Each frame has its own configuration file, the framework of the integration of disaster often brings configurations, such as the Spring and Struts integration, not only a Struts configuration file itself, not less, in Spring Action also needs to provide configuration information for each, and both need to comply with certain contract.

Framework and the framework with each other often occur between similar or duplicate functions, how to choose, how to use the often difficult for developers. Such as Spring AOP method itself provides a cache function to return the results, and Hibernate itself to provide two cache, whether both use it, or choose one from? The middle will often lead to much debate.

Framework integration problems have become increasingly prominent, we can find the open source community a large number of forums or discussion topics.

Currently there have been some attempts to solve the framework of the integration of open source projects, such as foreign AppFuse, domestic SpringSide, the integration of the framework to provide professional guidance. But there is no good solution to the actual needs of real development. The integrated framework in order to increase interoperability, network are spread too wide, leading to integration of the framework itself like a giant, daunting, and dexterity of the custom there, and reduce their utility, these integrated open source projects are often reduced to an instance of guiding.

Upgrade troubles

Active in the framework of the daily upgrade, feature-rich. Second, because of open source frameworks exist to some extent arbitrary, often leads to the actual use of the framework, we found lot of hidden Bug, it sometimes becomes inevitable upgrade to a frame. Open-source framework for formal specification than the Sun have a more flexible upgrade path, high and low version compatibility issues have become a common occurrence. Such as the famous Hibernate, the 3.0 version and 2.0 versions of the package names have undergone radical changes, just-released versions of Acegi and low very different, incompatible.

An integrated framework consists of a number of different team from the framework of the composition, integration framework in the framework of these combinations on high, the upgrade changes the underlying framework of the portfolio has caused a corresponding rise in the framework of the situation, the fragile stability of the integration framework is easily break.

The upgrade also has a direct combination of the framework development team brings the pressure of learning, in order to familiar with the framework of the new features and improvements in the development of spare time, they had to squeeze their spare time to learn continuously charge. Always a framework for learning the new features not yet been completed, another new version of the framework of another burst of cheers in the debut, allow developers to find all his efforts to just a horse ride a cow chasing the game.

3, the developer how to get out puzzle

Framework of explosive growth and the rapid pace of technological change, so just from traditional J2EE puzzle to get out of developers fall into a new dilemma. There are many personal experience of the developers a large fall in the line of grievances, and even many voices crying out, hope to return to JSP + JavaBean + JDBC to that era of innocence.

Framework of software development were also present to the world a fresh and happy, do not want to look forward to healthy individuals of the chaos into a holistic dispute. In the complicated puzzle out how the open source world and the plight of the ship to grasp the direction of their technology, is a meditative reverie every developers to do.

Focus on learning by analogy

Everyone's time is limited, for the periodic tight schedule anxious to work overtime and more so for the developers to make the developer could not "know the word all over the world to read the book to make world" learning-by-frame. Select good for themselves, for the project framework is particularly important focus of study. Not only master the technical details, but also to understand the framework of the principles and ideas, so that when in contact with the relevant framework, we can comprehend by analogy, identify what is true.

If you are in-depth understanding of the Struts MVC framework of principles and ideas, in contact with Tapestry, Spring MVC and other framework, you will find the difference between the two is metaphysical, rather than qualitative differences, even if the actual need for the framework really want to convert When you can easily smooth transition.







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Comparison Reference Tools

Characteristics of GIS

1. Spatial visualization (Spatial Visualizaiton)

a. profile feature space visualization of surface features

Information System is a computer simulation of the real world, and a geographical information system was highlighted its space on the relation between the real world. Use our space for all things in the state has a very intuitive feel. No matter that the screen can display a stepless zoom the map and information inquiries, or show a three-dimensional terrain model is bringing us right Xianshi spatial relationship of Renshi world more intuitive and specific. Perhaps we can use computer science in the popular "WYSIWYG" word to explain this.

b. the characteristics of surface features with spatial reference attribute information visualization feature

GIS spatial visualization of features include the right features on spatial distribution of attribute information Patterns Visualization This is a geographic information system is an important feature to ensure, that GIS 瀹炵幇 spatial information and attribute information integrated management, and to well established links between the two. For example, the use of one of China's administrative division map, we can extract the geographic information system database provinces, municipalities and autonomous regions in 1994 census data to calculate population density, population density, according to the classification index to specify a different color and fill displayed by the corresponding administrative polygons (this implementation is a space from the property to the association process), this property features room for thematic surface features can be achieved through the geographic information system tools for spatial visualization of reference information.

2. Spatial orientation (Spatial Navigation)

The use of geographical information systems, we can not only global overview of the study area, but also can zoom and roaming and other basic functions of GIS provides more depth to our area of interest to study.

A complete geographic information system provides a spatial database capabilities, we can use a small scale view of the overall and partial view of scale to large scale view details. Growing at the same time scale to show the spatial information content to the user will be constantly updated. For example, an administrative province in view the overall situation, only need to display large rivers, provincial, and municipal and county roads, railways and administrative district polygons and other global information, and, with the continuous increase of scale, we need to show that cases of land, buildings, park space for specific surface features. These and Cartography emphasized the concept of integrated graphics is similar.

GIS spatial orientation features can be reflected in spatial query functions. Cases using a provincial-level land use maps, we can query to find space "in the city park," and immediately zoom the map display range to all the "park" within the spatial distribution, such as the embodiment of space-oriented role .

3. Spatial thinking (Spatial Thinking)

GIS spatial database in the storage space around the object descriptions, it is also storing the spatial relationships between surface features, this feature is to provide a foundation for spatial analysis.

GIS spatial thinking is to use GIS database has stored the information, through GIS tools (such as buffer analysis, overlay analysis), generated in the GIS spatial database and information storage requirements.

Geographic information system will integrate a number of spatial analysis tools, and provide secondary development tools. Conducting spatial analysis, the user will be a variety of tools to research by the professional model organized into a program (ie the computer can identify and operation of thought), by 鍦扮悊 information system was completed, provided at the end results of the analysis of spatial visualization .

GIS spatial thinking allows us to reveal the spatial relationship, spatial distribution patterns and spatial trends, and other types of information systems can not complete the task.

Urban and Regional Planning is the geographic information system technology embodies the characteristics of spatial thinking, the most typical applications.






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Another pair of eyes CMMI [2]

I am confident has been understood for more in-depth 6sigma; However, when I more in-depth understanding of CMMI, the more I believe it is a good way to research and development. But why do we in R & D process improvement or progress slowly? I think there are two reasons: First, all alone in the face of a variety of ideas and effective work, the capacity will be neither effective combination, so that effective progress of the work, did not dare give up a number of decisions to adhere to a number. Second, even in the decision-making, the organization's execution can not keep up. Improvements to our current terms, and finally a clear improvement in the development process in order to CMMI-based, this is a clear idea of work; in practice, in accordance with CMMI project management specifications for each stage targeted, clear responsibility , track time, so the results highlighted. If he continues, I have no doubt that to achieve the set goals.

Some people may soon have to ask: do you not 6sigma the Black Belt? If so, should 6sigma doing here? I am a black belt, but I do not exist in order to make 6sigma I EPG positions in order to complete the requirements to work: research and development process improvement. Either way then, can organizations achieve their goals as long as like. And, as mentioned above, CMMI can do the planning and implementation, 6sigma can do, just similar to it. However, in order to organize specific ideas, consistency, a party of some necessary concessions. It is "a gentleman doing something not done," clearly the work of leading ideas, the need 6sigma do certain things. In addition, 6sigma still more details in place, add help for the development of process improvement. If a variety of tools to enhance thinking and decision-making logic, as far as possible data for decision-making will also promote the organization and improve the measurement of interest; and CMMI process improvement in the measure of the lack of financial returns, but also 6sigma exposed in front of it also promote the organization to improve in this area. Not only these, 6sigma desire for perfection, customer focus, team communication, and dissemination of knowledge and concepts of regular training, are subtly changing the atmosphere of the organization to improve the quality of members. All this is quietly driving the development process improvements, and results must be organized in the CMMI maturity level assessment, the farther high.







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