Question { 14004 }

What is the auto correlation function of a discrete time
white noise?

Answer

when a signal is transmitted it might be mixed with noise so
to check weather it can be recovered back by eleminating the
noise . to do this we go for auto correlation of the signal
if the ampiltude at the zero is max in the auto correlated
sequence then the signal can be recovered .
auto correlation is nothing but a process of comparision.

Question { 15148 }

tell me site from where i can download WREN N MARTIN
GRAMMER BOOK...

Answer

go to linkstore.blogspot.com u can find it there
and also many others
i am not this blog owner dont think to advertise i am
sending this

Question { Wipro, 18829 }

what is SNR?? WHY IT IS IMPORTANT IN COMMUNICATION NETWORK?

Answer

what girish siad above is for sure right but if noise is
dominant over message signal then message wont be lost just
it would be distorted. to over come this we go for digital
communication where it is more immune to noise.
a communication is said to very good if its SNR is very high.

Question { 6203 }

what is the physical need to find 3bd frequencies?

Answer

The theory is that 3dB differences are "just perceptible,"
so a speaker whose response curve lies within that tolerance
window is a reasonably accurate speaker.

or

As a rough rule of thumb, a change of 3 dB at mid
frequencies is just noticeable by the average person.

or
mathematically to say
It is the half power point. At this point, the
electronic/communication system has achieved the maximum
power transfer.

Question { 9298 }

among the chebsew and butterworth filter which is more
efficient?

Answer

i think chebsew is more efficient

Question { 17276 }

what does d-flip flop stand for?means what is d there?

Answer

as vinay says d stands for data is not right as far as my
knowledge coz d can also be delay flip flop as d-flip flop
is also used to generate delay