1. Modulation What is modulation?
a process of changing one or more properties of the analog carrier in proportion to the information signal.
One of the characteristics of the carrier signal is changed according to the variations of the modulating signal.
AM – amplitude, E
FM – frequency , ω
PM - phase , θ

2. Modulation (cont’d) Why modulation is needed?
To generate a modulated signal suited and compatible to the characteristics of the transmission channel.
For ease radiation and reduction of antenna size
Reduction of noise and interference
Channel assignment
Increase transmission speed

3. Noise, interference and distortion
unwanted signals that coincide with the desired signals.
Two type of noise:internal and external noise.
Internal noise
Caused by internal devices/components in the circuits.
External noise
noise that is generated outside the circuit.
E.g. atmospheric noise,solar noise, cosmic noise, man made noise.

4. Noise, interference and distortion (Cont’d)
Contamination by extraneous signals from human sources.
E.g. from other transmitters, power lines and machineries.
Occurs most often in radio systems whose receiving antennas usually intercept several signals at the same time
One type of noise.

5. Noise, interference and distortion (Cont’d)
Signals or waves perturbation caused by imperfect response of the system to the desired signal itself.
May be corrected or reduced with the help of equalizers.

6. Limitations in communication system
A) Technological problems
Includes equipment availability, economic factors, federal regulations and interaction with existing systems.
Problem solved in theory but perfect solutions may not be practical.

7. Limitations in communication system (cont’d)
B) Physicals limitations
i) Bandwidth limitation
Measure of speed
The system ability to follow signal variations depends on the transmission bandwidth.
Available bandwidth determines the maximum signal speed.

8. Limitations in communication system (cont’d)
ii) Noise limitation
Unavoidable.
The kinetic theory.
Noise relative to an information signal is measured in terms of signal to noise ratio (SNR).

9. Communication system design
Compromise within:
Transmission time and power
SNR performance
Cost of equipments
Channel capacity
Bandwidth

10. FREQUENCY AND WAVELENGTH
Cycle - One complete occurrence of a repeating wave (periodic signal) such as one positive and one negative alternation of a sine wave.
Frequency - the number of cycles of a signal that occur in one second.
Period - the time distance between two similar points on a periodic wave.
Wavelength - the distance traveled by an electromagnetic (radio) wave during one period.

11. PERIOD AND FREQUENCY COMPARED
T = One period
time
One cycle
Frequency = f = 1/T

12. Frequency and wavelength compared+ T
time
f = 1/T 
distance

13. CALCULATING WAVELENGTH AND FREQUENCY
 = wavelength in meters
f = frequency in MHz
C = f 
where C = 3 x 108 m/s (speed of light)

14. THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ
Wavelength
( = 300/f)
107 m
106 m
105 m
104 m
103 m
10-1 m
10-2 m
10-3 m
10-4 m
102 m
10 m
1 m
Millimeter
waves
ELF VF
VLF LF MF HF
VHF
UHF
SHF
EHF
30 Hz
3 kHz
300 Hz
30 kHz
3 MHz
3 GHz
300 kHz
30 MHz
30 GHz
300 MHz
300 GHz
(f = 300/)
Frequency

15. LOW AND MEDIUM FREQUENCIES
Extremely Low Frequencies - 30 to 300 Hz
Voice Frequencies to 3000 Hz
Very Low Frequencies - 3 kHz to 30 kHz
Low Frequencies - 30 kHz to 300 kHz
Medium Frequencies kHz to 3 MHz

16. HIGH FREQUENCIES High Frequencies - 3 MHz to 30 MHz
Very High Frequencies - 30 MHz to 300 MHz
Ultra High Frequencies MHz to 3 GHz
(1 GHz and above = microwaves)
Super High Frequencies - 3 GHz to 30 GHz
Extremely High Frequencies - 30 GHz to 300 GHz

18. Public Broadcast Frequencies
Longwave AM Radio = kHz (LF)
Mediumwave AM Radio = 535kHz kHz (MF)
TV Band I (Channels 2 - 6) = 54MHz - 88MHz (VHF)
FM Radio Band II = 88MHz - 108MHz (VHF)
TV Band III (Channels ) = 174MHz - 216MHz (VHF)
TV Bands IV & V (Channels ) = 470MHz - 806MHz (UHF)

19. FCC Channel Bandwidth Allocations
Designation Frequency Range No. of Channels Bandwidth
AM broadcast kHz – 1605 kHz kHz
Citizen band MHz – MHz kHz
FM broadcast MHz – 108 MHz kHz
TV broadcast MHz – 806 MHz MHz
FCC : Federal Communications Commission, United States

20. THE ELECTROMAGNETIC SPECTRUM ABOVE 300 GHZ
Wavelength
0.8 x 10-6 m
0.4 x 10-6 m
10-3 m
10-4 m
10-5 m
Millimeter
waves
Ultraviolet
Infrared
X-rays
Visible
Gamma rays
Cosmic rays
300 GHz

21. OPTICAL FREQUENCIES Infrared - 0.7 to 10 micron
Visible light to 0.8 micron
Ultraviolet - Shorter than 0.4 micron
Note: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

22. TYPES OF COMMUNICATIONSTX
Channel RX
Simplex:
One-way
Duplex:
Two-way
Half duplex:
Alternate TX/RX
Full duplex:
Simultaneous
TX/RX TX RX
Channel(s) TX RX

23. COMMUNICATIONS SIGNAL VARIATIONS
Baseband - The original information signal such as audio, video, or computer data. Can be analog or digital.
Broadband - The baseband signal modulates or modifies a carrier signal, which is usually a sine wave at a frequency much higher than the baseband signal.

24. Frequency Spectrum &Bandwidth
The frequency spectrum of a waveform consists of all frequencies contained in the waveform and their amplitudes plotted in the frequency domain.
The bandwidth of a frequency spectrum is the range of frequencies contained in the spectrum. It is calculated by subtracting the lowest frequency from the highest.

25. Frequency Spectrum &Bandwidth (cont’d)
Bandwidth of the information signal equals to the difference between the highest and lowest frequency contained in the signal.
Similarly, bandwidth of communication channel is the difference between the highest and lowest frequency that the channel allow to pass through it

26. Gain and Loss Electronic System Pin Pout Vin Vout Iin Iout
W2-3
Gain and Loss
Pin
Pout
Electronic
System
Vin
Vout
Iin
Iout
If ratio Pout /Pin > 1 , power gain.
If ratio Pout /Pin < 1 , power loss.
If ratio Vout /Vin > 1 , voltage gain.
If ratio Vout /Vin < 1 , voltage loss.
If ratio Iout /Iin > 1 , current gain.
If ratio Iout /Iin < 1 , current loss.

27. Signal Gain Voltage amplifier: Av= Vo/Vi.
Transistors current gain:  = ic/ib,
Step-up voltage transformer, Vsecondary > Vprimary
Step-up current transformer, Isecondary > Iprimary
In some cases, signal gain may be >1 eventhough the power gain is < 1.
Occasionally, a signal loss or power loss is also called
as signal attenuation or power attenuation.

28. Power Gain It is the ratio of output power over input power.
Ap = Po/Pi.
In amplifiers, the power gain may be more than one. The signal power is amplified. DC power supply is transformed into signal power.

29. Power and voltage gains in communication
The term decibels (dB) is a relative unit of measurement
used frequently in electronic communication to describe
gain or loss.
Power gain in dB = 10 log (Po/Pi)
Voltage gain in dB = 20 log (Vo/Vi)

30. Power ratio Po/Pi = 10,000 = 40 dB
Voltage ratio Vo/Vi = = 40 dB.
See that Po/Pi = (Vo/Vi)2
hence, (Po/Pi) dB = 2(Vo/Vi)dB

31. Alternatively: Voltage gain ratio = 10 (gain in dB/20) Example 1:
Power gain ratio = 10 (gain in dB/10)
Voltage gain ratio = 10 (gain in dB/20)
Example 1:
Convert a power gain of 64 dB into ratio.
64 dB = 10(64/10) = 10(6.4) = x 106

32. Example 2 :
What is the dB gain or loss for a certain system when the
Power out of a certain system is 0.01 times the power in?
In this case, Pout= 0.01 Pin
Therefore, Power gain (dB)= 10 log(0.01)
= -20 dB
When the answer is negative, indicates a loss or
attenuation.

33. Example 3:
Let there be two amplifiers in cascade as shown. Their gains are 13 dB and 10 dB respectively.
The overall gain at the output is = 23 dB.
Output A1 A2
13dB gain
10dB gain

34. In terms of ratio:
23 dB = 10(23/10)= 200
13 dB = 10(13/10)= 20
10 dB = 10(10/10)= 10
Again 20 x 10 = 200.

35. Relative dB
It is convenient to express signals with some reference such as
1mW power or,
1 V voltage level.
This permits input- and output- signals to be expressed in terms of relative dB.
When referenced to 1mW, it is written dBm
When referenced to 1 V, it is written as dBV
When referenced to 1W, it is written dBW
When referenced to 1 V, it is written as dBV

36. Relative dB is not an absolute gain but is termed as gain with respect to a reference unit.
Examples :
a) For a 5 watts signal in reference to 1mW,
the relative dB; 10 log(5W/1mW) = dBm
b) For a 500 V signal in reference to a 1 V ,
the relative dB; 20 log(500 V /1 V ) = 53.98dB V