| 词条 | Multi-frequency receiver |
| 释义 |
Multi-Frequency signalling, (MF), is similar to the European version, CCITT Signaling System 5, (SS5). The original format was five tones used in pairs. This later evolved to six tones. Because its six tones are used only in pairs, this signaling format is sometimes referred to as "two-out-of-five code" or "two of six." Multi-Frequency receivers have been present in US telephony at least since the late 1940s. In 1940s technology, receivers in 4XB and similar equipment used vacuum tubes. Later ones used RC filters and transistors. Digital filters became commonplace in electronic switching systems of the 1980s. For example, in 5ESS switch such jobs were done by DSPs in the Global Digital Services Unit (GDSU). References
2 : Telephony signals|Telephony equipment |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。