In 1596 , english navigator sir francis drake died off the coast of panama ; he was buried at sea off puerto bello , panama , in a lead coffin 1596年，英国航海家法兰西斯德雷克，于巴拿马外海航行时过世；遗体置于铅棺而海葬于巴拿马波多贝约。 （德雷克为第一个环球航行的英国船长，曾击败西班牙无敌舰队。 ）
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Rtce is based on forecasting the inherent vulnerabilities to propagation of hf time - varying channel , including multipath delay , doppler spread , selective fading , interference , so this paper also introduces characteristics of hf channel in the beginning . familiar rtce systems all adopt envelope method that bello brought forward 实时选频技术是基于对短波电离层时变信道固有的不利于电波传播的各种因素，包括信道的多径展宽、多普勒展宽、选择性衰落、噪声干扰等的预测的基础上实现的，所以在开篇对短波信道的特点进行了详细的介绍。
