T 7.2.1.3 Amplitude Modulation

TPS 7.2.1.3
Contents
Contents
Equipment overview ..............................................................................................................7
Symbols and abbreviations .................................................................................................... 8
Schrifttum .............................................................................................................................. 8
1 Introduction ......................................................................................................................... 9
Signals9
Time and spectral domain...................................................................................................... 10
Modulation ............................................................................................................................ 10
The communications system according to Shannon.............................................................. 12
2 Measuring instruments ..................................................................................................... 13
2.1 Oscilloscope and spectrum analyzer .......................................................................... 13
2.2 Equipment descriptions .............................................................................................. 16
726 94 Spectrum analyzer .......................................................................................... 16
726 961 Function generator 200kHz .......................................................................... 17
726 99 Frequency counter 0..10 MHz ...................................................................... 18
736 201 CF transmitter 20 kHz .................................................................................. 18
736 221 CF receiver 20 kHz ...................................................................................... 19
2.3 A measurement example ........................................................................................... 20
3 Review of amplitude modulation (AM) .......................................................................... 23
The spectrum of amplitude modulation ................................................................................. 24
Representing amplitude modulation with a vector diagram ................................................... 24
AM demodulation .................................................................................................................. 25
Questions ............................................................................................................................... 26
4 Required equipment and accessories ............................................................................. 28
Training objectives: ................................................................................................................ 28
5 Double Sideband-AM ........................................................................................................ 29
The DSB SC
. ............................................................................................................................ 29
5.1 Investigations on the dynamic characteristic of the DSB .......................................... 30
5.1.1 DSB ............................................................................................................................ 30
5.1.2 DSB SC
................................................................................................................................................................................................................31
5.2 Spectrum of the DSB................................................................................................. 31
5.2.1 DSB ............................................................................................................................ 31
5.2.2 DSB SC
................................................................................................................................................................................................................33
5.2.3 The AM spectrum for modulation with a square-wave signal .................................. 33
5.3 AM demodulation (synchronous demodulation) ........................................................ 34
5.3.1 DSB ............................................................................................................................ 34
5.3.2 Carrier recovery ........................................................................................................ 35
5.3.3 DSB SC
Demodulation ................................................................................................. 37
5.4 Beats .......................................................................................................................... 37
5