FM遥测解调自动极性纠反功能的改进设计

An Improved Design for Auto Polarity Revising of FM Telemetry Demodulation

针对FM遥测解调在高误码条件下出现的极性误反转问题,从传输信道不同的高低差变频方式会导致频谱反转进而导致解调极性反转出发,引出了自动极性纠反功能的设计背景。通过详述帧极性检测标识在搜索和校核、锁定两种不同状态下的判决逻辑,分析了原自动极性纠反功能的设计原理,结合模拟验证试验,揭示了原判决逻辑在帧极性检测标识第二次判1过程中不够严格,未考虑到高误码也可造成反码出现后帧极性检测标识被误判1的设计缺陷。将帧极性检测标识第二次判1逻辑改进为异或累加结果超过帧同步码组长的一半而非滑动相关峰值,解决了缺陷问题又兼顾了检测的快速性,通过改进后的验证试验证明了改进设计的正确性和有效性。

This paper proposes the background of automatic polarity correction function of telemetry demodulation unit from the false polarity revising by high error code under the different channel frequency conversion mode. Then it analyzes the principle of automatic polarity correction design by two kinds of judge logic of identifying the frame polarity under the searching state and the chechout/lock state. With the evidence of the simulating test the bug has been found that high error code can result in error on the second identifying wheather the frame polarity equals 1 after the frame polarity synchronization reverse code emerges. Finally, the bug is removed by adopting the modification of identifying the frame polarity as 1 just by whether difference probability accumulation exceeds half length of frame synchronization code. By such modification it not only removes the bug but also assm＇es the identifying＇s speediness. As a result of the test after the modification, the new design has been approved to be correct and effective.