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1、无线电调幅图象研究高中物理教科书在“电磁场和电磁波”一章“无线电波的发射和接收”一节中，有关无线电调幅的知识有“在电磁波发射技术中，使电磁波随各种信号而改变叫调制。使高频震荡的振幅随信号而改变叫做调幅，调幅广播（AM）一般使用中波和短波波段。”的内容。（见人民教育出版社物理室编著 全日制普通中学教科书（必修加选修）物理第二册第245页）。以前，对这个内容不容易说清楚，现在，可以借助电子计算机的Exel把它讲明白。1 等幅高频振荡实际的高频振荡（例如中波段）为535-1605kHz，短波段的频率更高。频率太高，在图象中看不出来，为说明问题，我们把三角函数设为y=sin16x，以区别于声音信号（低
2、频信号）。而声音信号设为y=sin2x。在-到2的范围内设定自变量x, 为求图象的清晰，间隔设为0.01，求出对应的y=sin16x的值，在求值过程中注意把x的数值转化为弧度。表1和图1分别为数据表和图象。xcos16x-11-0.990.876307-0.980.535827-0.970.062791-0.96-0.42578-0.95-0.80902-0.94-0.99211-0.93-0.92978-0.92-0.63742-0.91-0.18738-0.90.309017-0.890.728969-0.880.968583-0.870.968583-0.860.728969-0.850
3、.309017-0.84-0.18738-0.83-0.63742-0.82-0.92978-0.81-0.99211-0.8-0.80902-0.79-0.42578-0.780.062791-0.770.535827-0.760.876307-0.751-0.740.876307-0.730.535827-0.720.062791-0.71-0.42578-0.7-0.80902-0.69-0.99211-0.68-0.92978-0.67-0.63742-0.66-0.18738-0.650.309017-0.640.728969-0.630.968583-0.620.968583-0.
4、610.728969-0.60.309017-0.59-0.18738-0.58-0.63742-0.57-0.92978-0.56-0.99211-0.55-0.80902-0.54-0.42578-0.530.062791-0.520.535827-0.510.876307-0.51-0.490.876307-0.480.535827-0.470.062791-0.46-0.42578-0.45-0.80902-0.44-0.99211-0.43-0.92978-0.42-0.63742-0.41-0.18738-0.40.309017-0.390.728969-0.380.968583-
5、0.370.968583-0.360.728969-0.350.309017-0.34-0.18738-0.33-0.63742-0.32-0.92978-0.31-0.99211-0.3-0.80902-0.29-0.42578-0.280.062791-0.270.535827-0.260.876307-0.251-0.240.876307-0.230.535827-0.220.062791-0.21-0.42578-0.2-0.80902-0.19-0.99211-0.18-0.92978-0.17-0.63742-0.16-0.18738-0.150.309017-0.140.7289
6、69-0.130.968583-0.120.968583-0.110.728969-0.10.309017-0.09-0.18738-0.08-0.63742-0.07-0.92978-0.06-0.99211-0.05-0.80902-0.04-0.42578-0.030.062791-0.020.535827-0.010.876307010.010.8763070.020.5358270.030.0627910.04-0.425780.05-0.809020.06-0.992110.07-0.929780.08-0.637420.09-0.187380.10.3090170.110.728
7、9690.120.9685830.130.9685830.140.7289690.150.3090170.16-0.187380.17-0.637420.18-0.929780.19-0.992110.2-0.809020.21-0.425780.220.0627910.230.5358270.240.8763070.2510.260.8763070.270.5358270.280.0627910.29-0.425780.3-0.809020.31-0.992110.32-0.929780.33-0.637420.34-0.187380.350.3090170.360.7289690.370.
8、9685830.380.9685830.390.7289690.40.3090170.41-0.187380.42-0.637420.43-0.929780.44-0.992110.45-0.809020.46-0.425780.470.0627910.480.5358270.490.8763070.510.510.8763070.520.5358270.530.0627910.54-0.425780.55-0.809020.56-0.992110.57-0.929780.58-0.637420.59-0.187380.60.3090170.610.7289690.620.9685830.63
9、0.9685830.640.7289690.650.3090170.66-0.187380.67-0.637420.68-0.929780.69-0.992110.7-0.809020.71-0.425780.720.0627910.730.5358270.740.8763070.7510.760.8763070.770.5358270.780.0627910.79-0.425780.8-0.809020.81-0.992110.82-0.929780.83-0.637420.84-0.187380.850.3090170.860.7289690.870.9685830.880.9685830
10、.890.7289690.90.3090170.91-0.187380.92-0.637420.93-0.929780.94-0.992110.95-0.809020.96-0.425780.970.0627910.980.5358270.990.876307111.010.8763071.020.5358271.030.0627911.04-0.425781.05-0.809021.06-0.992111.07-0.929781.08-0.637421.09-0.187381.10.3090171.110.7289691.120.9685831.130.9685831.140.7289691
11、.150.3090171.16-0.187381.17-0.637421.18-0.929781.19-0.992111.2-0.809021.21-0.425781.220.0627911.230.5358271.240.8763071.2511.260.8763071.270.5358271.280.0627911.29-0.425781.3-0.809021.31-0.992111.32-0.929781.33-0.637421.34-0.187381.350.3090171.360.7289691.370.9685831.380.9685831.390.7289691.40.30901
12、71.41-0.187381.42-0.637421.43-0.929781.44-0.992111.45-0.809021.46-0.425781.470.0627911.480.5358271.490.8763071.51表1 x与cos16x数据表图1 y=cos16x图象2 低频声音信号在-到2的范围内设定自变量x,，间隔同样设为0.01，求出对应的y=sin2x的值，然后画出图象。表2和图2分别为数据表和图象。x cos2x-11-0.990.998027-0.980.992115-0.970.982287-0.960.968583-0.950.951057-0.940.929776-0.930.904827-0.920.876307-0.910.844328-0.90.809017-0.890.770513-0.880.728969-0.870.684547-0.860.637424-0.850.587785-0.840.535827-0.830.481754-0.820.425779-0.810.368125-0.80.309017-0.790.24869-0.780.187381-0.770.125333-0.760.062791-0.75-1.8E-16-0.74-0.0627
