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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-11-0.990.876307-0.98待添加的隐藏文字内容20.535827-0.970.062791-0.96-0.42578-0.95-0.80902-0.94-0.99211-0.93-0.92978-0.92-0.63742-0.91-0.18738-0.90.309017-0.890.728969-0.880.968583-0.870.968583-0.860.7
3、28969-0.850.309017-0.84-0.18738-0.83-0.63742-0.82-0.92978-0.81-0.99211-0.8-0.80902-0.79-0.42578-0.780.062791-0.770.535827-0.760.876307-0.751-0.740.876307-0.730.535827-0.720.062791-0.71-0.42578-0.7-0.80902-0.69-0.99211-0.68-0.92978-0.67-0.63742-0.66-0.18738-0.650.309017-0.640.728969-0.630.968583-0.62
4、0.968583-0.610.728969-0.60.309017-0.59-0.18738-0.58-0.63742-0.57-0.92978-0.56-0.99211-0.55-0.80902-0.54-0.42578-0.530.062791-0.520.535827-0.510.876307-0.51-0.490.876307-0.480.535827-0.470.062791-0.46-0.42578-0.45-0.80902-0.44-0.99211-0.43-0.92978-0.42-0.63742-0.41-0.18738-0.40.309017-0.390.728969-0.
5、380.968583-0.370.968583-0.360.728969-0.350.309017-0.34-0.18738-0.33-0.63742-0.32-0.92978-0.31-0.99211-0.3-0.80902-0.29-0.42578-0.280.062791-0.270.535827-0.260.876307-0.251-0.240.876307-0.230.535827-0.220.062791-0.21-0.42578-0.2-0.80902-0.19-0.99211-0.18-0.92978-0.17-0.63742-0.16-0.18738-0.150.309017
6、-0.140.728969-0.130.968583-0.120.968583-0.110.728969-0.10.309017-0.09-0.18738-0.08-0.63742-0.07-0.92978-0.06-0.99211-0.05-0.80902-0.04-0.42578-0.030.062791-0.020.535827-0.010.876307010.010.8763070.020.5358270.030.0627910.04-0.425780.05-0.809020.06-0.992110.07-0.929780.08-0.637420.09-0.187380.10.3090
7、170.110.7289690.120.9685830.130.9685830.140.7289690.150.3090170.16-0.187380.17-0.637420.18-0.929780.19-0.992110.2-0.809020.21-0.425780.220.0627910.230.5358270.240.8763070.2510.260.8763070.270.5358270.280.0627910.29-0.425780.3-0.809020.31-0.992110.32-0.929780.33-0.637420.34-0.187380.350.3090170.360.7
8、289690.370.9685830.380.9685830.390.7289690.40.3090170.41-0.187380.42-0.637420.43-0.929780.44-0.992110.45-0.809020.46-0.425780.470.0627910.480.5358270.490.8763070.510.510.8763070.520.5358270.530.0627910.54-0.425780.55-0.809020.56-0.992110.57-0.929780.58-0.637420.59-0.187380.60.3090170.610.7289690.620
9、.9685830.630.9685830.640.7289690.650.3090170.66-0.187380.67-0.637420.68-0.929780.69-0.992110.7-0.809020.71-0.425780.720.0627910.730.5358270.740.8763070.7510.760.8763070.770.5358270.780.0627910.79-0.425780.8-0.809020.81-0.992110.82-0.929780.83-0.637420.84-0.187380.850.3090170.860.7289690.870.9685830.
10、880.9685830.890.7289690.90.3090170.91-0.187380.92-0.637420.93-0.929780.94-0.992110.95-0.809020.96-0.425780.970.0627910.980.5358270.990.876307111.010.8763071.020.5358271.030.0627911.04-0.425781.05-0.809021.06-0.992111.07-0.929781.08-0.637421.09-0.187381.10.3090171.110.7289691.120.9685831.130.9685831.
11、140.7289691.150.3090171.16-0.187381.17-0.637421.18-0.929781.19-0.992111.2-0.809021.21-0.425781.220.0627911.230.5358271.240.8763071.2511.260.8763071.270.5358271.280.0627911.29-0.425781.3-0.809021.31-0.992111.32-0.929781.33-0.637421.34-0.187381.350.3090171.360.7289691.370.9685831.380.9685831.390.72896
12、91.40.3090171.41-0.187381.42-0.637421.43-0.929781.44-0.992111.45-0.809021.46-0.425781.470.0627911.480.5358271.490.8763071.51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
13、.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-16-0.74-0.06279-0.73-0.12533-0.72-0.18738-0.71-
14、0.24869-0.7-0.30902-0.69-0.36812-0.68-0.42578-0.67-0.48175-0.66-0.53583-0.65-0.58779-0.64-0.63742-0.63-0.68455-0.62-0.72897-0.61-0.77051-0.6-0.80902-0.59-0.84433-0.58-0.87631-0.57-0.90483-0.56-0.92978-0.55-0.95106-0.54-0.96858-0.53-0.98229-0.52-0.99211-0.51-0.99803-0.5-1-0.49-0.99803-0.48-0.99211-0.
15、47-0.98229-0.46-0.96858-0.45-0.95106-0.44-0.92978-0.43-0.90483-0.42-0.87631-0.41-0.84433-0.4-0.80902-0.39-0.77051-0.38-0.72897-0.37-0.68455-0.36-0.63742-0.35-0.58779-0.34-0.53583-0.33-0.48175-0.32-0.42578-0.31-0.36812-0.3-0.30902-0.29-0.24869-0.28-0.18738-0.27-0.12533-0.26-0.06279-0.256.28E-15-0.240
16、.062791-0.230.125333-0.220.187381-0.210.24869-0.20.309017-0.190.368125-0.180.425779-0.170.481754-0.160.535827-0.150.587785-0.140.637424-0.130.684547-0.120.728969-0.110.770513-0.10.809017-0.090.844328-0.080.876307-0.070.904827-0.060.929776-0.050.951057-0.040.968583-0.030.982287-0.020.992115-0.010.998
17、027010.010.9980270.020.9921150.030.9822870.040.9685830.050.9510570.060.9297760.070.9048270.080.8763070.090.8443280.10.8090170.110.7705130.120.7289690.130.6845470.140.6374240.150.5877850.160.5358270.170.4817540.180.4257790.190.3681250.20.3090170.210.248690.220.1873810.230.1253330.240.0627910.256.13E-
18、170.26-0.062790.27-0.125330.28-0.187380.29-0.248690.3-0.309020.31-0.368120.32-0.425780.33-0.481750.34-0.535830.35-0.587790.36-0.637420.37-0.684550.38-0.728970.39-0.770510.4-0.809020.41-0.844330.42-0.876310.43-0.904830.44-0.929780.45-0.951060.46-0.968580.47-0.982290.48-0.992110.49-0.998030.5-10.51-0.
19、998030.52-0.992110.53-0.982290.54-0.968580.55-0.951060.56-0.929780.57-0.904830.58-0.876310.59-0.844330.6-0.809020.61-0.770510.62-0.728970.63-0.684550.64-0.637420.65-0.587790.66-0.535830.67-0.481750.68-0.425780.69-0.368120.7-0.309020.71-0.248690.72-0.187380.73-0.125330.74-0.062790.75-1.8E-160.760.062
20、7910.770.1253330.780.1873810.790.248690.80.3090170.810.3681250.820.4257790.830.4817540.840.5358270.850.5877850.860.6374240.870.6845470.880.7289690.890.7705130.90.8090170.910.8443280.920.8763070.930.9048270.940.9297760.950.9510570.960.9685830.970.9822870.980.9921150.990.998027111.010.9980271.020.9921
21、151.030.9822871.040.9685831.050.9510571.060.9297761.070.9048271.080.8763071.090.8443281.10.8090171.110.7705131.120.7289691.130.6845471.140.6374241.150.5877851.160.5358271.170.4817541.180.4257791.190.3681251.20.3090171.210.248691.220.1873811.230.1253331.240.0627911.253.06E-161.26-0.062791.27-0.125331
22、.28-0.187381.29-0.248691.3-0.309021.31-0.368121.32-0.425781.33-0.481751.34-0.535831.35-0.587791.36-0.637421.37-0.684551.38-0.728971.39-0.770511.4-0.809021.41-0.844331.42-0.876311.43-0.904831.44-0.929781.45-0.951061.46-0.968581.47-0.982291.48-0.992111.49-0.998031.5-1图2 y=cos2x的图象3 调幅在同一幅图中画出y1=cos2x,
23、 y2=-cos2x, y3=cos2xcos16x的图象，数据表和图象分别如表3和图3所示。xcos2x-cos2xcos2xcos16x-11-11-0.990.998027-0.998030.874577-0.980.992115-0.992110.531602-0.970.982287-0.982290.061678-0.960.968583-0.96858-0.4124-0.950.951057-0.95106-0.76942-0.940.929776-0.92978-0.92244-0.930.904827-0.90483-0.84129-0.920.876307-0.87631-
24、0.55858-0.910.844328-0.84433-0.15821-0.90.809017-0.809020.25-0.890.770513-0.770510.56168-0.880.728969-0.728970.706067-0.870.684547-0.684550.663041-0.860.637424-0.637420.464662-0.850.587785-0.587790.181636-0.840.535827-0.53583-0.1004-0.830.481754-0.48175-0.30708-0.820.425779-0.42578-0.39588-0.810.368
25、125-0.36812-0.36522-0.80.309017-0.30902-0.25-0.790.24869-0.24869-0.10589-0.780.187381-0.187380.011766-0.770.125333-0.125330.067157-0.760.062791-0.062790.055024-0.75-1.8E-161.84E-16-1.8E-16-0.74-0.062790.062791-0.05502-0.73-0.125330.125333-0.06716-0.72-0.187380.187381-0.01177-0.71-0.248690.248690.105
26、887-0.7-0.309020.3090170.25-0.69-0.368120.3681250.365222-0.68-0.425780.4257790.39588-0.67-0.481750.4817540.307081-0.66-0.535830.5358270.100404-0.65-0.587790.587785-0.18164-0.64-0.637420.637424-0.46466-0.63-0.684550.684547-0.66304-0.62-0.728970.728969-0.70607-0.61-0.770510.770513-0.56168-0.6-0.809020
27、.809017-0.25-0.59-0.844330.8443280.158211-0.58-0.876310.8763070.558579-0.57-0.904830.9048270.841287-0.56-0.929780.9297760.922445-0.55-0.951060.9510570.769421-0.54-0.968580.9685830.412403-0.53-0.982290.982287-0.06168-0.52-0.992110.992115-0.5316-0.51-0.998030.998027-0.87458-0.5-11-1-0.49-0.998030.9980
28、27-0.87458-0.48-0.992110.992115-0.5316-0.47-0.982290.982287-0.06168-0.46-0.968580.9685830.412403-0.45-0.951060.9510570.769421-0.44-0.929780.9297760.922445-0.43-0.904830.9048270.841287-0.42-0.876310.8763070.558579-0.41-0.844330.8443280.158211-0.4-0.809020.809017-0.25-0.39-0.770510.770513-0.56168-0.38
29、-0.728970.728969-0.70607-0.37-0.684550.684547-0.66304-0.36-0.637420.637424-0.46466-0.35-0.587790.587785-0.18164-0.34-0.535830.5358270.100404-0.33-0.481750.4817540.307081-0.32-0.425780.4257790.39588-0.31-0.368120.3681250.365222-0.3-0.309020.3090170.25-0.29-0.248690.248690.105887-0.28-0.187380.187381-
30、0.01177-0.27-0.125330.125333-0.06716-0.26-0.062790.062791-0.05502-0.256.28E-15-6.3E-156.28E-15-0.240.062791-0.062790.055024-0.230.125333-0.125330.067157-0.220.187381-0.187380.011766-0.210.24869-0.24869-0.10589-0.20.309017-0.30902-0.25-0.190.368125-0.36812-0.36522-0.180.425779-0.42578-0.39588-0.170.4
31、81754-0.48175-0.30708-0.160.535827-0.53583-0.1004-0.150.587785-0.587790.181636-0.140.637424-0.637420.464662-0.130.684547-0.684550.663041-0.120.728969-0.728970.706067-0.110.770513-0.770510.56168-0.10.809017-0.809020.25-0.090.844328-0.84433-0.15821-0.080.876307-0.87631-0.55858-0.070.904827-0.90483-0.8
32、4129-0.060.929776-0.92978-0.92244-0.050.951057-0.95106-0.76942-0.040.968583-0.96858-0.4124-0.030.982287-0.982290.061678-0.020.992115-0.992110.531602-0.010.998027-0.998030.87457701-110.010.998027-0.998030.8745770.020.992115-0.992110.5316020.030.982287-0.982290.0616780.040.968583-0.96858-0.41240.050.9
33、51057-0.95106-0.769420.060.929776-0.92978-0.922440.070.904827-0.90483-0.841290.080.876307-0.87631-0.558580.090.844328-0.84433-0.158210.10.809017-0.809020.250.110.770513-0.770510.561680.120.728969-0.728970.7060670.130.684547-0.684550.6630410.140.637424-0.637420.4646620.150.587785-0.587790.1816360.160
34、.535827-0.53583-0.10040.170.481754-0.48175-0.307080.180.425779-0.42578-0.395880.190.368125-0.36812-0.365220.20.309017-0.30902-0.250.210.24869-0.24869-0.105890.220.187381-0.187380.0117660.230.125333-0.125330.0671570.240.062791-0.062790.0550240.256.13E-17-6.1E-176.13E-170.26-0.062790.062791-0.055020.2
35、7-0.125330.125333-0.067160.28-0.187380.187381-0.011770.29-0.248690.248690.1058870.3-0.309020.3090170.250.31-0.368120.3681250.3652220.32-0.425780.4257790.395880.33-0.481750.4817540.3070810.34-0.535830.5358270.1004040.35-0.587790.587785-0.181640.36-0.637420.637424-0.464660.37-0.684550.684547-0.663040.
36、38-0.728970.728969-0.706070.39-0.770510.770513-0.561680.4-0.809020.809017-0.250.41-0.844330.8443280.1582110.42-0.876310.8763070.5585790.43-0.904830.9048270.8412870.44-0.929780.9297760.9224450.45-0.951060.9510570.7694210.46-0.968580.9685830.4124030.47-0.982290.982287-0.061680.48-0.992110.992115-0.531
37、60.49-0.998030.998027-0.874580.5-11-10.51-0.998030.998027-0.874580.52-0.992110.992115-0.53160.53-0.982290.982287-0.061680.54-0.968580.9685830.4124030.55-0.951060.9510570.7694210.56-0.929780.9297760.9224450.57-0.904830.9048270.8412870.58-0.876310.8763070.5585790.59-0.844330.8443280.1582110.6-0.809020
38、.809017-0.250.61-0.770510.770513-0.561680.62-0.728970.728969-0.706070.63-0.684550.684547-0.663040.64-0.637420.637424-0.464660.65-0.587790.587785-0.181640.66-0.535830.5358270.1004040.67-0.481750.4817540.3070810.68-0.425780.4257790.395880.69-0.368120.3681250.3652220.7-0.309020.3090170.250.71-0.248690.248690.1058870.72-0.187380.187381-0.011770.73-0.125330.125333-0.067160.74-0.062790.062791-0.055020.75-1.8E-161.84E-16-1.8E-16