【正文】 port loss exhibited by the star coupler was dB177。這種雙速能力在 1553B 的基礎(chǔ)上可以對(duì)現(xiàn)有的系統(tǒng)提供高速改造的能力，并且允許系統(tǒng)升級(jí)而變的更好。每當(dāng)總線控制要求傳輸從一個(gè)有著高速附加電路的 1553B 到到另外一個(gè)有著 相同配置的用戶時(shí)， 20Mb/s 的傳輸?shù)谋銜?huì)開始。 圖 3 雙冗余光纖 15638/20Mbit 的總線配置 光纖接口單元是直接連接到 1553B 的輸 入輸出端口的與用戶相關(guān)的設(shè)備，并提供了必要的三電平的 1553B 信號(hào)格式和雙層的光學(xué)格式的轉(zhuǎn)化。 圖 4 光纖總線配置展示的高速測(cè)試設(shè)備 示范系統(tǒng)光纖總線的硬件 示范系統(tǒng)光纖總線的結(jié)構(gòu)可用現(xiàn)成的光纖器件來實(shí)現(xiàn)。本系統(tǒng)的設(shè)計(jì)到較小的轉(zhuǎn)化版本如一個(gè)單一的SEME 模塊 是可行的。電纜包含 1001140微米的梯度折射率纖維，廣泛的應(yīng)用于生產(chǎn) AVS/B鷂 Ⅱ 戰(zhàn)斗機(jī) 。高速數(shù)據(jù)實(shí)際被遠(yuǎn)程終端及其相關(guān) 1553B 總線控制器所請(qǐng)求而發(fā)送。列在最后一欄的價(jià)值標(biāo)準(zhǔn)是對(duì)所采取的兩個(gè)通道的 13 個(gè)原型的單元的測(cè)量結(jié)果。圖 5 給出了消息序列在組成高速測(cè)試機(jī) 組的元件之間的傳輸。隨著航空電子設(shè)備的應(yīng)用包括在總線上演示系統(tǒng)的低速設(shè)備只與之關(guān)聯(lián)的 1553B總線 ,檢驗(yàn)員研制設(shè)計(jì)了高速的光纖接口單元。T，作為一個(gè)接近 34 毫瓦分貝（平均）的靈敏度 10 誤碼率（ BER），并采用簡(jiǎn)化的邊緣檢測(cè)算法。這些按在用戶外部家具設(shè)備上的單元已經(jīng)被證實(shí)了，并且可直接進(jìn)入 1553B 的連接器中。這就要求光纖總線接口直接可以和 任何 1553B 的 I/O 連接器連接，而且可以與任何合法的 1553B 接口電平相適應(yīng)。每一個(gè)星型耦合器的輸出被隨后連接回光纖接口單元的輸入。這樣做的目的是利用現(xiàn)有的技術(shù) ,因而減少開發(fā)時(shí)間和成本。 這種方法的描述，在這個(gè)方面提供了用單一的光纖總線為媒介，使總線節(jié)點(diǎn)在 1 Mb/s 和 24 Mb/s 并存運(yùn)行，每一個(gè) 1 Mb/s 的接口是在 1553B 總線上兼容的，并且可以利用現(xiàn)成的硬件和軟件，目前已經(jīng)證實(shí)， 1 Mb/s 的 1553B 總線兼容接口和 20Mb/s 的新操作 設(shè)備可以同時(shí)工作在單總線結(jié)構(gòu)上，這種設(shè)計(jì)為從目前 1 Mb/s 的設(shè)備過渡到一個(gè)合并了現(xiàn)存兼容的 1553B 總線和最新更高速度的一種統(tǒng)一的總線結(jié)構(gòu)提供了一種合理的，低風(fēng)險(xiǎn)的方法。ITL) logic chips and discrete ponents. Mounted on each of these boards was an optical transmitter and an optical receiver. Translation of this design to smaller versions such as a single SEME Module is feasible. The optical transmitter chosen for this application was a highradiance light emitting diode (LED).The diode was operated at less than full output, launching dBm (average) optical power into 100 micron core fiber. The dual speed optical receiver was packaged in a module measuring 3 for mounting onto the logic and levelshift board. This burstcapable device, developed by ATamp。T Fiber Optic 1553/MSDRT Data Bus provides an efficient means of improving the data handling capabilities of the 1553B data bus. Through the use of fiber optics and high speed digital multiplexing techniques, a single fiber optic bus can provide both 1 Mb/s and 20 Mb/s transmission capability when supported by 1553B bus hardware. The 20 Mb/s operation is based on the Multiple Speed Data Rate Transmission (MSDRT) concept, which involves multiplexing 20 Mb/s data with standard 1553B protocol in a manner which is invisible to 1 Mb/s users. This dualspeed capability provides retrofit highspeed capability to existing systems based on 1553B, and allows for graceful system growth in the event of system upgrades. A dual speed single fiber transmission bus was chosen over an approach using separate busses for 1 Mb/s transmission and for higher speed transmission because the single fiber bus approach is more reliable, less expensive, and lighter weight. The fiber optic bus is patible with 1553B hardware, application and protocol software, and error handling routines, resulting in reduced cost and schedule impact for future technology upgrades. In addition, the use of fiber optics offers inherent immunity to electromagic interference, RF interference, electromagic pulses