# amplitude modulation..?

Status
Not open for further replies.

#### tavakoli

##### Member level 3
amplitude modulation+kennedy

what is the difference between amplitude modulation & dsb-sc modulation..?

B

#### boot_strap

##### Guest
spectrum of dsb-sc where wc>>wm

in amplitude modulation your modulated signal is : xc(t) = x(t)*A*cos(wt)

but dsb-sc is :

xc(t) = (1+k*x(t))*A*cos(wt)
for details go to haykins communication book..!

#### artem

dsbsc amplitude modulation

The difference is that AM modulation does contain the carrier frequency , but DSB does not .
Common part is that both modulation provides 2 bands = Fcarrier -+ Fmodulating

#### nandopg

##### Full Member level 4
dsb sc am modulation index

Regarding an AM-DSB modulator fed by a sine wave modulating signal wm and carrier frequency wc:
In the frequency domain: the spectrum is made up by three lines: one centered in wc, one centered in wc+wm and other centered in wc-wm
In time domain: The amplitude of the carrier will be changing according to the instantaneous value of wm. If the amplitude of wm is equal to the amplitude of wm, the modulated signal's amplitude will be changing from 0 and 2 x amplitude of wm (or wc). In this case the AM coefficient index is 100%. If you disconnect the modulating signal, the output of the modulator will be the a sine wave in wm.

Regarding an AM-DSB-SC modulator fed by a sine wave modulating signal wm and carrier frequency wc:
In the frequency domain: the spectrum is made up two lines: one centered in wc+wm and other centered in wc-wm. The carier is suppressed.
In time domain the modulated signal will be changing from 0 to the amplitude of wc. There is no definition of modulation index. If you turn off the modulating frequency, the modulator's output will be zero.
Now the most important characteristic of the AM-DSB-SC, is that the phase of the modulated signal jumps 180 deg. each time the modulating signal inverts its polariity.
By the way due to this characteristic AM-DSB-SC are the kind of modulator used to generate digital modulation in BPSK and QPSK.

NandoPG

#### awan

dsb sc modulation

in a.m the signal is modulated by amplitude

V

#### v_naren

##### Guest
am modulation with no carrier

another main point is that in full AM you waste power in the carrier signal frequency in addition to the side band informarion power

but in DSB-SC AM one does not waste any power as the carrier signal is not present...

#### cedance

am modulation am sc

awan said:
in a.m the signal is modulated by amplitude

and what modulation is DSBSC? same amplitude. what were u trying to say?

/cedance

V

#### v_naren

##### Guest
comparison between dsb sc and dscac

cedance said:
awan said:
in a.m the signal is modulated by amplitude

and what modulation is DSBSC? same amplitude. what were u trying to say?

/cedance

If I may answer this question

normal AM-FC (AM with full carrier)

$v_{AM-FC}(t)=V_c cos({\omega_0}t) (1+m(t))$
where m(t) is a scaled version of the the modulating or baseband signal that is to be transmitted, such that
[tex:6f8647dd41]|m(t)|<=1[/tex:6f8647dd41]

Double Side-band Suppressed Carrier (DSB-SC)
$V_{DSB-SC}(t)=V_c cos({\omega_0}t) m(t)$
where m(t) is the modulating or baseband signal that is to be transmitted.

Last edited:

#### djalli

difference between amplitude ,dsbsc, ssb

Another differences are money, management and situation. Engineering is business to be honest.

#### aman

##### Member level 5
what is dsbsc

pls consult the foolwing url for ur ans

http://www.eas.asu.edu/~midle/jdsp/commex/Lab1(Amplitude%20mod).htm

#### truebs

##### Full Member level 5
difference between am and dsb-sc

Amplitude modulation can be done in a number of ways...one among them is DSB Sc , the difference lies in two points :
1. Number of Sideband
2. Carrier signal.

In AM there can be either one or two sideband but the carrier signal is always sent with the modulated signal.

Whereas DSB has two sidebands and the carrier is suppressed.

What this implies is there would be no carrier signal with the modulated signal,this would have several implications on Bandwdth.
DSB Sc is considered superior to AM due to its lesser BW requirement and better S/N ratio (for proper design ).

Refer to Analog and Digital Communication Techniques by Couch for more details.

#### electron_boy

##### Full Member level 3
amplitude modulation is waste of power

amplitude modulation includes the transmission of the carrier. if the carrier is removed then it is DSB SC

#### CAP

##### Junior Member level 3
dsbsc by kannedy

electron_boy said:
amplitude modulation includes the transmission of the carrier. if the carrier is removed then it is DSB SC

why ? DSB SC have the carrier to. anothe way its not a SC

DSB have too sites of signal spektrum.
SSB have only one.

#### electron_boy

##### Full Member level 3
dsb-sc modulation

CAP said:
electron_boy said:
amplitude modulation includes the transmission of the carrier. if the carrier is removed then it is DSB SC

why ? DSB SC have the carrier to. anothe way its not a SC

DSB have too sites of signal spektrum.
SSB have only one.

then what the term 'suppressed carrier' mean??

V

#### v_naren

##### Guest
dsbsc modulation by kannedy

electron_boy said:
CAP said:
electron_boy said:
amplitude modulation includes the transmission of the carrier. if the carrier is removed then it is DSB SC

why ? DSB SC have the carrier to. anothe way its not a SC

DSB have too sites of signal spektrum.
SSB have only one.

then what the term 'suppressed carrier' mean??

electron_boy is correct...but sometimes the carrier is not completely removed. Its power is reduced relative to the sidebands. This is to facilitate "synchronous demodulation" in RXCVRs where a phase locked loop mechanism is used to "lock" and generate an in-phase LO signal and then this LO and the DSB-SC AM signal are both fed into a mixer to downconvert and hence perform demodulation to recover the transmitted baseband signal.

http://www.ece.eps.hw.ac.uk/Modules/B33cl2/cl-8-03.pdf

Section 8.6

In particular 8.6.2 to 8.6.3

:-D

#### checkmate

difference between am and dsb-sc signal

It really just means "do not include carrier frequency component". Coherent demodulation would then have to be done using other synchronization techniques such as PLLs.

#### CAP

##### Junior Member level 3
amplitude modulation index

often the term 'suppressed carrier' mean, that there are NO diskrete component at the F=SC in signal PSD.

it's there, but its spread about hole usefull bandwidth by phase/frequence/amplitude modulation.

#### TnT

##### Junior Member level 1
amplitude modulation with no carrier

What about the S/N ratio of AM and DSB modulation ?
This is the difference. In analog modulation, people allways want to increase S/N ratio

#### pankaj waghmare

##### Junior Member level 3
best book for amplitudemodulation

in dsb-sc,limitations of am is removed.
it saves transmitted power and supress the carrier
for detail plz refer g.kennedy`s book

#### ppenday

##### Member level 4
normal amplitude modulation Ù…Ø§ Ù…Ø¹Ù†Ù‰

am contains carrier and ds-sc does not. you can find much about this in communication systems by simon haykin.

Status
Not open for further replies.