some communication question?

[abhineet22]

BPFSK is more efficient than BFSK in presence of noise. Why?
What is meant by pre-emphasis and de-emphasis?
What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
What do you mean by ASCII, EBCDIC?

 

[icon]

The frequency either above which or below which the output of a circuit, such as a line, amplifier, or filter, is reduced to the specified level of - 3dB = 70.1% of the reference voltage level of 0dB = 100%.

A level drop of - 3dB means a voltage reduction to 70,1 % and also a power reduction to 50%, because V2 is proportional to P.

thats why it is not 1 dB..ok

In telecommunication, preemphasis is a system process designed to increase, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation differences or saturation of recording media in subsequent parts of the system. That is the mirror of the Deemphasis. The whole system is called Emphasis. The frequency curve is decided by especial time constants. The Cutoff frequency can be calculated from that value.

Preemphasis is commonly used in digital audio recording, record cutting and in FM broadcasting transmissions.

ASCII-American standard code for information interchange and EBCDIC extended binary coded decimal interchange form

serach it in google for further answers.....

 

[esourour]

BPSK is better that BFSK since In BPSK you get less nunber of bit errors for the same transmitted power. The cost of this is a little bit more complex receiver where the receiver has estimate the phase of the signal to be able to distinguish the two possible phases in BPSK. This is called "coherent receiver". In BFSK the phase is not needed and the receiver is simpler.