卫星通信第7章改.ppt

  1. 1、本文档共27页,可阅读全部内容。
  2. 2、有哪些信誉好的足球投注网站(book118)网站文档一经付费(服务费),不意味着购买了该文档的版权,仅供个人/单位学习、研究之用,不得用于商业用途,未经授权,严禁复制、发行、汇编、翻译或者网络传播等,侵权必究。
  3. 3、本站所有内容均由合作方或网友上传,本站不对文档的完整性、权威性及其观点立场正确性做任何保证或承诺!文档内容仅供研究参考,付费前请自行鉴别。如您付费,意味着您自己接受本站规则且自行承担风险,本站不退款、不进行额外附加服务;查看《如何避免下载的几个坑》。如果您已付费下载过本站文档,您可以点击 这里二次下载
  4. 4、如文档侵犯商业秘密、侵犯著作权、侵犯人身权等,请点击“版权申诉”(推荐),也可以打举报电话:400-050-0827(电话支持时间:9:00-18:30)。
查看更多
卫星通信第7章改

* * Chapter 7 The Space Segment 7.7 Transponder The advantage of the TWT over other types of tube amplifiers is that it can provide amplification over a very wide bandwidth. Input levels to the TWT must be carefully controlled, however, to minimize the effects of certain forms of distortion. * * Chapter 7 The Space Segment 7.7 Transponder At low input powers, the output-input power relationship is linear. The point of maximum power output being known as the saturation point. The saturation point is a very convenient reference point. The linear region of the TWT is defined as the region bound by the thermal noise limit at the low end and by what is termed the 1-dB compression point at the upper end. The absolute time delay between input and output signals at a fixed input level is generally not significant. At higher input levels, where more of the beam energy is converted to output power, the average beam velocity is reduced, and therefore, the delay time is increased. This results in a phase shift which varies with input level. Denoting the phase shift at saturation by θs and in general by θ, the phase difference relative to saturation is θ - θs. This is plotted in Fig. as a function of input power. Thus, this is termed AM/PM conversion. * * Chapter 7 The Space Segment 7.7 Transponder * * Chapter 7 The Space Segment 7.7 Transponder Frequency modulation (FM) is usually employed in analog satellite communications circuits. However, unwanted amplitude modulation (AM) can occur from the filtering which takes place prior to the TWT input. * * Chapter 7 The Space Segment 7.7 Transponder A TWT also may be called on to amplify two or more carriers simultaneously, this being referred to as multicarrier operation. The nonlinear transfer characteristic introduces a more serious form of distortion known as intermodulation distortion.Usually only the third-order contribution is hard limiter. At frequencies f1 and f2, these will give rise to frequencies 2f2 -fl and 2

文档评论(0)

dajuhyy + 关注
实名认证
内容提供者

该用户很懒,什么也没介绍

1亿VIP精品文档

相关文档