question answare

Good books for communication
1. http://www.scribd.com/doc/32470461/Book-Sol-Man-Modern-Digital-and-Analog-Communications-Systems-B-P-Lathi
2.Comm Electronics: Prin & Applns 3/E   By Frenzel
http://books.google.co.in/books?id=bydJMQydxFgC&pg=PA84&lpg=PA84&dq=The+maximum+allowed+deviation+of+the+FM+sound+signal+in+TV+is+25KHz.+If+the+actual+deviation+is+18KHz,+the+percent+modulation+is&source=bl&ots=bhazx-kKc2&sig=4FWCQo3JumTFnuK2ZbOyQeKTfcM&hl=en&sa=X&ei=A8uQUJ-nLIaErQek8oGgDw&ved=0CCsQ6AEwAQ#v=onepage&q=The%20maximum%20allowed%20deviation%20of%20the%20FM%20sound%20signal%20in%20TV%20is%2025KHz.%20If%20the%20actual%20deviation%20is%2018KHz%2C%20the%20percent%20modulation%20is&f=false



http://local.eleceng.uct.ac.za/courses/EEE3086F/notes/502-AM_DSB-SC_2up.pdf
http://www.studydroid.com/index.php?page=viewPack&packId=343785
http://www.morpheustechnology.com/ebooks/Wireless/03%20Amplitude%20Modulation.htm
http://www.scribd.com/doc/67932941/Frenzel

Pre Emphasis

Pre emphasis is nothing but enhanging the message signal 
and it is used for Transmission time.

De Emphasis

De Emphasis nothing but the comprese the message signal and 
it is used for receiving time.

Solution: By using Bessel’s Table, a modulation index of 4, has 7 significant sidebands.

Modulation index

"The ratio of the frequency deviation to the modulating frequency is known as the modulation index."

Symbolized by m

M = fd/fm (in radians)  Where

fd = frequency deviation

fm = modulating frequency

For example, assume that the maximum frequency deviation of the carrier is ± 25 KHz while the maximum modulating frequency is 10 KHz. The modulation index, therefore, is

mf = 25/10 = 2.5 rad

Note
The modulation index can originally know as the modulation factor; hence the symbol mf.

Note

The modulation index is a measure of radian phase shift of the modulated FM signal compared to the phase of the un-modulated carrier alone.
In most communications systems using FM, maximum limits are put on both the frequency deviation and modulating frequency. For example, in standard FM broadcasting, the maximum permitted frequency deviation is 75 KHz, while the maximum permitted modulating frequency is 15 KHz. This produces a modulation index of

mf = 75/15 = 5 rad.

Whenever the maximum allowable frequency deviation and the maximum modulating frequency are used in computing the modulation index, mf is known as the deviation ratio.

The audio broadcast in T.V. is transmitted by FM. The maximum deviation permitted is 25 KHz and the maximum modulating frequency is 15 KHz. This produces a deviation ratio of

d = 25/15 = 1.67 rad

In standard two-way mobile radio communications using FM, the maximum permitted deviation is usually 5 KHz. The upper modulating frequency is usually limited to 2.5 KHz which is high enough for intelligible voice transmission. This produces a deviation ratio of

d = 5/2.5 = 2 rad

Percentage of Modulation

The maximum deviation permitted can be used in a radio with the actual carrier deviation to produce a percentage of modulation for FM. Remember, in commercial FM broadcasting the maximum allowed deviation is 75 KHz. If the modulating signal is producing only a maximum deviation of 60 KHz, then the FM percentage of modulation is

FM percent modulation

= (Actual carrier deviation/Maximum carrier deviation) * 100 
= (60/75) x 100 
= 80%

Frequency Deviation

The change in carrier frequency is called the frequency deviation." and uses symbol ∆fc (∆ is the Greek letter delta and is used to symbolize change). For a sample transmitter with an assigned rest frequency of 100MHzdeviated by ±25KHz, The carrier change frequency with modulation between the limits of 99.975 .MHz and 100.025 MHz The total frequency change of 2 x 25 KHz = 50 KHz is called the carrier swing.

Frequency Swing

"Frequency swing is the total deviation above and below the center frequency."

It is the total frequency change above and below the center frequency. In above example, frequency swing is 50 KHz. It is also called the carrier swing.






Read more: http://www.daenotes.com/electronics/communication-system/terms-modulation#ixzz2ArDTGDKe

Which of the following is not a major benefit of FM over AM?






A.  Capture effect




B.  Greater efficiency




C.  Noise immunity




D.  Lower complexity and cost

Question Excerpt From FRENZEL CHAPTER 4: FREQUENCY MODULATION

Q.1) 
The amount of frequency deviation from the carrier center frequency in an FM transmitter is proportional to what characteristic of the modulating signal?



A.
Amplitude


B.
Frequency


C.
Phase


D.
Shape


Q.2) 
Both FM and PM are types of what kind of modulation?



A.
Amplitude


B.
Phase


C.
Angle


D.
Duty Cycle


Q.3) 
If the amplitude of the modulating signal decreases, the carrier deviation



A.
Increases


B.
Decreases


C.
Remains constant


D.
Goes to zero


Q.4) 
On an FM signal, maximum deviation occurs at what point on the modulating signal?



A.
Zero crossing points


B.
Peak positive amplitude


C.
Peak negative amplitude


D.
Both B and C


Q.5) 
In PM, a frequency shift occurs while what characteristic of the modulating signal is changing?



A.
Shape


B.
Phase


C.
Frequency


D.
Amplitude


Q.6) 
Maximum frequency deviation of a PM signal occurs at



A.
Zero crossing points


B.
Peak positive amplitude


C.
Peak negative amplitude


D.
Peak positive or negative amplitude


Q.7) 
In PM, carrier frequency deviation is not proportional to



A.
Modulating signal amplitude


B.
Carrier amplitude and frequency


C.
Modulating signal frequency


D.
Modulator phase shift


Q.8) 
To compensate for increases in carrier frequency deviation with an increase in modulating signal frequency, what circuit is used between the modulating signal and the phase modulator?



A.
Low pass filter


B.
High pass filter


C.
Phase shifter


D.
Bandpass filter


Q.9) 
The FM produced by PM is called



A.
FM


B.
PM


C.
Indirect FM


D.
Indirect PM


Q.10) 
If the amplitude of the modulating signal applied to a phase modulator is constant, the output signal will be



A.
Zero


B.
The carrier frequency


C.
Above the carrier frequency


D.
Below the carrier frequency


Q.11) 
A 100 MHz carrier is deviated 50 KHz by a 4KHz signal. The modulation index is



A.
5


B.
8


C.
12.5


D.
20


Q.12) 
The maximum deviation of an FM carrier is 2KHz by a maximum modulating signal of 400Hz. The deviation ratio is



A.
0.2


B.
5


C.
8


D.
40


Q.13) 
A 70 KHz carrier has a frequency deviation of 4KHz with a 1000Hz signal. How many significant sideband pairs are produced?



A.
4


B.
5


C.
6


D.
7


Q.14) 
What is the relative amplitude of the third pair of sidebands of an FM signal with m=6?



A.
0.11


B.
0.17


C.
0.24


D.
0.36


Q.15) 
A 200KHz carrier is modulated by a 2.5KHz signal. The fourth pair of sidebands are spaced from the carrier by



A.
2.5KHz


B.
5KHz


C.
10KHz


D.
15KHz


Q.16) 
An FM transmitter has a maximum deviation of 12 KHz and a maxium modulating frequency of 12 KHz. The bandwidth by Carson's rule is



A.
24KHz


B.
33.6KHz


C.
36.8KHz


D.
48KHz


Q.17) 
The maximum allowed deviation of the FM sound signal in TV is 25KHz. If the actual deviation is 18KHz, the percent modulation is



A.
43 percent


B.
72 percent


C.
96 percent


D.
139 percent


Q.18) 
Which of the following is not a major benefit of FM over AM?



A.
Greater efficiency


B.
Noise immunity


C.
Capture effect


D.
Lower complexity and cost


Q.19) 
The primary disadvantage of FM is its



A.
Higher cost and complexity


B.
Excessive use of spectrum space


C.
Noise susceptibility


D.
Lower efficiency


Q.20) 
Noise is primarily



A.
High frequency spikes


B.
Low frequency variations


C.
Random level shifts


D.
Random frequency variations


Q.21) 
The receiver circuit that rids FM of noise is the



A.
Modulator


B.
Demodulator


C.
Limiter


D.
Low pass filter


Q.22) 
The phenomenon of a strong FM signal dominating a weaker signal on a common frequency is referred to as the



A.
Capture effect


B.
Blot out


C.
Quieting factor


D.
Domination syndrome


Q.23) 
The AM signals generated at a low level may only be amplified by what type of amplifier?



A.
Op Amp


B.
Linear


C.
Class C


D.
Push-pull


Q.24) 
Frequency modulation transmitters are more efficient because their power is increased by what type of amplifier?



A.
Class A


B.
Class B


C.
Class C


D.
All of the above


Q.25) 
Noise interfere mainly with modulating signals that are



A.
Sinusoidal


B.
Nonsinusoidal


C.
Low frequencies


D.
High frequencies


Q.26) 
Pre emphasis circuits boost what modulating frequencies before modulation?



A.
High frequencies


B.
Mid range frequencies


C.
Low frequencies


D.
All of the above


Q.27) 
A pre emphasis circuit is a



A.
Low pass filter


B.
High pass filter


C.
Phase shifter


D.
Bandpass filter


Q.28) 
Pre emphasis is compensated for at the receiver by a 



A.
Phase inverter


B.
Bandpass filter


C.
High pass filter


D.
Low pass filter


Q.29) 
The cutoff frequency of pre-emphasis and de-emphasis circuits is



A.
1KHz


B.
2122KHz


C.
5KHz


D.
75KHz




http://www.proprofs.com/quiz-school/story.php?title=frenzel-chapter-4-frequency-modulation