tailieunhanh - Improving Bit by Bit

To move signals of that frequency around efficiently within my transmitting station needed what can only be described as plumbing transmission lines made out of thin copper pipes and ceramic insulators—the alternative being expensive, specially constructed, but very high loss, coaxial cable. Yet here we are twenty years later happily shoving similar frequencies down twisted pairs without really thinking about the physics involved! Three factors about radio frequency signals are very important in understanding our problem:. | O KRONE. Improving Bit by Bit. AS DATA RATES ROSE many installers and customers are finding that physical networks designed installed and tested to the current Cat 5e or proposed Cat 6 standards simply won t work properly at 100 Megabit Fast Ethernet let alone at Gigabit speeds. Independent Management Consultant Philip Turtle explains some of the reasons why this is happening and how one manufacturer seems to have come up with the solution. There have been numerous reports during the latter half of 1999 about Cat 5e and proposed Cat 6 systems being installed and passing category testing. Yet when presented with real network traffic they have failed to pass data sensibly at all even though the link lights on the network interface cards NICs are on both on the PC and the hub or switch. The practical solution in many cases has been to switch the 100 Mb s NICs from Full Duplex to Half Duplex effectively halving the theoretical maximum bandwidth to 50 Mb s and in fact taking the practical bandwidth much lower. It s all about radio waves. As a teenager I was a keen ham radio practitioner and built a VHF radio station operating on the two meter band at frequencies around 144 MHz. Why do I tell you this Because Cat 5 systems use 100 MHz rated components and cable Cat 6 uses 200 MHz both very close to my radio station frequency. Figure 1 To move signals of that frequency around efficiently within my transmitting station needed what can only be described as plumbing transmission lines made out of thin copper pipes and ceramic insulators the alternative being expensive specially constructed but very high loss coaxial cable. Yet here we are twenty years later happily shoving similar frequencies down twisted pairs without really thinking about the physics involved Three factors about radio frequency signals are very important in understanding our problem 1. They become attenuated very rapidly in a transmission line system such as our twisted pair and the power loss increases .