Amplitude Modulation (Am)

LAB REPORT AMPLITUDE MODULATION

NAME

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STU. ID No

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Group

:A

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Output Wave forms.

Fm(t) signa

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Output "a#$ %oms o&s$r#$' & os!ios!op$

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*ON*LUSION •

Observed how the Timedomain signal and the frequency donation s ignal of Amplitude Modulated signal behaved.

DIS*USSION

Modulation indices are described for various forms of modulation. The amplitude modulation, AM, modula mod ulatio tion n ind inde e can be def define ined d as the measure measure of etent etent of amp amplit litude ude variation variation about an un! modulated carrier. As with other modulation indices, the modulation inde for amplitude modulation, AM, indicates the amount by which the modulated carrier varies around its static un!modulated level. A complementary figure to modulation inde is also used for amplitude modulation signals. "nown as the modulation depth, it is typically the modulation inde epressed as a percentage. Typically the modulation inde of  a signal will vary as the modulating signal intensity varies. #owever some static values enable the various levels to visuali$ed more easily.

Ampitu'$ mo'uat$' in'$+ o% ,.-

When the modulation inde reaches %.&, i.e. a modulation depth of %&&', the carrier level falls to $ero and rise to twice its non!modulated level.

Ampitu'$ mo'uat$' in'$+ o% .,

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Ampitu'$ mo'uat$' in'$+ o% mor$ t/an ., i.$. o#$r0mo'uat$'

roadcast stations in particular ta-e measures to ensure that the carries of their transmissions never   become over modulated. The transmitters incorporate limiters to prevent more than %&&' modulation. #over they also normally incorporate automatic audio gain controls to -eep the audio levels such that near %&&' modulation levels are achieved for most of the time.ingle sideband modulation can be viewed as an amplitude modulation signal with elements removed or reduced. /n order to see how single sideband is created, it is necessary to use an amplitude modulated signal as the starting point.

An ampitu'$ mo'uat$' !arri$r s/o"ing si'$&an's $it/$r si'$ o% t/$ !arri$r

0rom this it can be seen that the signal has two sidebands, each the mirror of the other, and the carrier. To improve the efficient of the signal, both in terms of the power and spectrum usage, it is possible to remove the carrier, or at least reduce it, and remove one sideband ! one is the mirror image of the other. A single sideband signal therefore consists of a single sideband, and often no carrier, although the various variants of single sideband are detailed below.

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Sing$ si'$&an' mo'uation s/o"ing upp$r an' o"$r si'$&an'

/t can be seen that either the upper sideband can be used. There is no  between using either the upper or lower main criterion is to use the same sideband users for the given frequency band and upper sideband is more commonly used applications.

signas

sideband or lower   advantage sideband. The as used by other   application. The for professional