please ans these questions

[vjfaisal]

hi
here i need more help in the following questioins::

1) when a base band signal m(t)=2cos2000t+cos3000t is modulated using a carrier cos20000t, the frequency component in the USB of DSBSC are given in rad/sec. ( also mention the logic behind the answer or formula)

A. 17k and 18k
B. 22k and 23k
C. 18k and 22k
D.17k and 23k

2)
for tone modulation (AM/DSB with carrier) the power effeicency is ??


3)bandwith of the DSBSC signal, modulated with baseband signal with the band with 100 hz is ???

4)
for the message signal m(t) =sin(square)1000t the baseband frequencies in rad/sec are????

please ans these question if anyone have the answer.
its an urgent

best regards

 

[samasimo]

Re: please ans these questions!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

1) The base band frequencies are (-2k and -3k)LSB and (2k and 3K) USB
when modulated (shifted) by carrier freq of 20K

Therfore the USB will be 22k and 23K (answer number B)

2) 33% (assuming the question means m=1)

3) 100Hz

4) 0, -2K, 2K

 

[vjfaisal]

hi

please tell me how u solve these questions





best regards

 

[samasimo]

BASICS:
The frequency component of cos Wt are at W and -W (rad/sec)

Amp. Modulation shifts the signal compenents by +Wc and -Wc

****************************************************
1) The base band frequencies are (-2k and -3k)LSB and (2k and 3K) USB
when modulated (shifted) by carrier freq of 20K

Therfore the USB will be 22k and 23K (answer number B)
****************************************************
2) Tone means baseband signal is cos Wt and modulted by (cos Wc t)

eff = sidebands power / (carrier power + sidebands power)

in tone modulation, the eff <=33%

if m=1, eff =33%
****************************************************
3) Amp modulation DOES NOT change BW of signal so it remains 100
hz
*****************************************************
4) sin(square)1000t = 1 - cos(square)1000t = 1 - [0.5+0.5 cos 2000 t]
= 0.5-0.5 cos 2000 t

the first term ihas freq comp at 0
the second term has freq comp -2k and 2 k (rad/s)

 

[vjfaisal]

hi
i need th proof of intregation property of fourier transform.

if anybody have please upload it .





best regards