Introduction to Telecommunication 121009

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Introduction to Telecommunication(121009) Chris
Roeloffzen
Chair Telecommunication engineering (EWI) Floor
8 HOGEKAMP EL/TN building (north) Telephone 489
2804 E-mail c.g.h.roeloffzen_at_el.utwente.nl
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Contents of the course
Lecture 1 - 3 Introduction Chapter 1
Introduction to Electronic Communications Chapter
2 Signal Analysis and Mixing Lecture 4 - 7
CW modulation Chapter 4 Amplitude modulation,
Transmission Chapter 5 Amplitude modulation,
Reception Chapter 6 Single-side banded
Communication Systems Chapter 7 Angle
Modulation Transmission Chapter 8 Angle
Modulation Receivers Lecture 8 - 11
Media Chapter 12 Metallic Transmission
Lines Chapter 14 Electromagnetic Wave
Propagation Chapter 15 Antennas Chapter 13
Optical Fibers Lecture 12 - 14 Digital
Communication Chapter 9 Digital
Modulation Chapter 10 Digital
Transmission Lecture 15 16 ????????????????? Fo
r specific information see www.el.utwente.nl/tel/
education/courses.htm
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Today Lecture 5
Chapter 5 Amplitude Modulation Reception
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Chapter 5 Amplitude Modulation Reception

• What is Amplitude Demodulation?
• Synchronous Demodulation
• Amplitude Spectra
• AM Receivers
• Superheterodyne receiver
• Double Conversion AM Receiver
• Envelope detector and Beat Frequency Oscillator
  Receiver

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Demodulation of Linear Amplitude Modulated Signals

• Receiver
• receive
• amplify
• demodulate

AM demodulation is the reverse process of AM
modulation

• Synchronous demodulation
• Envelope detection

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Synchronous demodulation
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Synchronous demodulation
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Amplitude Spectra
frequency
fc
fc
frequency
?
frequency
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Amplitude Spectra
frequency
fc
fc
frequency
fc
frequency
2fc
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Amplitude Spectra
frequency
fc
fc
frequency
fc
frequency
2fc
Down conversion
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Synchronous demodulation Out of phase
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Synchronous demodulation Out of phase
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AM radio
Band 535 kHz 1605 kHz Bandwidth per channel
10 kHz Channel spacing 10 kHz
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AM receiver Block Diagram (1)
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AM receiver Block Diagram (2)
RF section
Bandpass Filter
Mixer/ converter section
Bandpass filter
IF section
Bandpass filter
AM detector
Bandpass filter
Audio section
fig 5-1
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Noncoherent Tuned Radio-Frequency Receiver
Antenna coupling network
RF amp.
RF amp.
RF amp.

• AM band??
• Quality factor Filter????

Audio detector
Audio amplifier
fig 5-3
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Noncoherent Tuned Radio-Frequency Receiver
Antenna coupling network
RF amp.
RF amp.
RF amp.

• AM 535 1605 kHz
• Channel BW 10 kHz
• Difficult to tune
• Q remains constant ? filter bandwidth varies

Audio detector
Audio amplifier
fig 5-3
Nonuniform selectivity
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Superheterodyne Receiver
RF-section
Mixer
Preselector
RF amplifier
oscillator
IF-section
Bandpass filter
IF amplifier
Audio detector
Audio amplifier
Fixed BPF at lower frequencies than RF
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Receiver RF input (535 1605 kHz)
RF-to-IF conversion
Preselector 535 - 565 kHz
565 kHz
535
545
555
Mixer
Oscillator 1005 kHz
high-side injection (fLO gt fRF)
IF filter 450 460 kHz
470 kHz
440
450
460
IF Filter output
450
460 kHz
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Receiver RF input (535 1605 kHz)
RF-to-IF conversion
Preselector 535 - 565 kHz
What is the use of the preselector ???
565 kHz
535
545
555
Mixer
Oscillator 1005 kHz
high-side injection (fLO gt fRF)
IF filter 450 460 kHz
470 kHz
440
450
460
IF Filter output
450
460 kHz
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Problem !!!!!!!
AM band is (535 1605 kHz)
flo
fIF
fIF
RF (550 kHz)
LO (1005 kHz)
IF (455 kHz)
IF Intermediate frequency
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Image frequency
flo
fim
fIF
fIF
fIF
RF
Image
LO
IF
Higher intermediate frequency (IF) better image
frequency rejectionbut more complicated
amplifiers and filters
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Example 1 AM-band
RF 600 kHz
Preselector
Primary task is Image frequency rejection
Mixer
Oscillator ?????
IF filter450 460 kHz
Center 455 kHz
LO ????????Image ?????????
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Example 1 AM-band
RF 600 kHz
Preselector
Primary task is Image frequency rejection
Mixer
Oscillator 1055 kHz
IF filter450 460 kHz
RFIFLO 600455 1055 kHzIFLOImage 4551055
1510 kHz
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Example 1
Q (600 kHz) 100 ? IFRR ???????????
Low Q
455 kHz
1055
600
1510
IF
RF
LO
Image
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Example 1
Q (600 kHz) 100 ? IFRR 211.3
Low Q
455 kHz
1055
600
1510
IF
RF
LO
Image
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Example 2 27 MHz band
RF 27 MHz
Preselector
high-side injection
Mixer
Oscillator ????
IF filter455 kHz
LO ????????Image ?????????
IFRR 211.3 ? Q ????
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Example 2 27 MHz band
RF 27 MHz
Preselector
Mixer
Oscillator 27.455 MHz
IF filter455 kHz
RFIFLO 27 MHz455 kHz 27.455
MHzIFLOImage 45527.455 27.91 MHz
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Example 2
IFRR 211.3 ? Q (27 MHz) 3167 Q (600 kHz)
100
High Q
Low Q
27.455
455 kHz
1055
27 MHz
600
1510
27.91
IF
RF
LO
Image
RF
Image
LO
Solution Use higher IF frequencies
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Example 3 27 MHz band
RF 27 MHz
Preselector
Mixer
Oscillator ?
IF filter5 MHz
instead of 455 kHz
LO ????????Image ?????????
IFRR 211.3 ? Q ????
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Example 3 27 MHz band
RF 27 MHz
Preselector
Mixer
Oscillator 32 MHz
IF filter5 MHz
RFIFLO 27 MHz5 MHz 32 MHzIFLOImage 5 MHz
32 MHz 37 MHz
IFRR 211.3 ? Q 330
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Example 3 27 MHz band
RF 27 MHz
Preselector
Mixer
Oscillator 32 MHz
IF filter5 MHz
Difficult to amplify and???
RFIFLO 27 MHz5 MHz 32 MHzIFLOImage 5 MHz
32 MHz 37 MHz
IFRR 211.3 ? Q 330
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High IF for good image frequency rejection Low
IF for good amplification and good channel
selection Solution ????
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Double-Conversion AM Receivers
IF 1
good IM rejection at high IF
Mixer
RF amplifierandPreselector
Bandpass filterIF 1
1st oscillator
IF 2
Mixer
IF2 amplifier
Bandpass filterIF2
To audio detector
2nd oscillator
good amplification at low IF
fig 5.35
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Gain and Loss
RF-section
Mixer
Preselector
RF amplifier
oscillator
Bandpass filter
IF amplifier
Audio detector
Audio amplifier
IF-section
Use dB !!!
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Envelope detector or Peak detector
D
IF-in
Audio out
R
C
?
Transfer function
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Envelope detection
D
IF-in
Audio out
R
C
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Envelope detection
for m70.7
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Beat frequency oscillator
Chapter 6 page 239 242 Noncoherent BFO receiver
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SSB envelope detection
Coherent BFO receiver
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SSB envelope detection
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Summary and Outlook
Synchronous demodulation Tuned Radio-Frequency
Receiver ? difficult to amplify and filter across
AM band Superheterodyne Receiver ? intermediate
frequency at low frequency for good amplifying
and filtering Image frequency ? preselector ?
intermediate frequency as high as possible for
good image frequency rejection Double conversion
as a solution AM Detector Peak detector and BFO
Next lecture Chapter 7 Angle modulation
transmission
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Receiver Parameters

• Selectivity
• Bandwidth Improvement
• Sensitivity
• Dynamic Range
• Fidelity
• Insertion Loss
• Noise Temperature

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Receiver Parameters Selectivity
SF Shape factor (unitless) B(-60 dB)
bandwidth 60 dB below maximum signal level B(-3
dB) bandwidth 3 dB below maximum signal level
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Receiver Parameters Bandwidth Improvement
SF bandwidth improvement (unitless) BRF RF
bandwidth (hertz) BIF IF bandwidth (hertz)
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Receiver Parameters Sensitivity
The sensitivity of a receiver is the minimum RF
signal level that can be detected at the input to
the receiver and still produce a usable
demodulated information signal. Expressed in µV
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Receiver Parameters Dynamic Range
The dynamic range of a receiver is defined as the
difference in decibels between the minimum input
level necessary to discern a signal and the input
level that will overdrive the receiver and
produce distortion. Expressed in dB
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Receiver Parameters Fidelity

• Fidelity is a measure of the ability of a
  communications system to produce, at the output
  of the receiver, an exact replica of the original
  source information.
• Three forms of distortion
• amplitude
• frequency
• phase

Why third-order distortion????
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Receiver Parameters Insertion Loss
Insertion Loss (IL) is a parameter associated
with the frequencies that fall within the
passband of a filter and is generally defined as
the ratio of the power transferred to a load with
a filter in the circuit to the power transferred
to a load without the filter
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Receiver Parameters Noise Temperature
T environmental temperature (Kelvin) N noise
power (watts) K Boltzmanns constant (1.38 10
-23 J/K) B total noise factor (hertz)
Te equivalent noise temperature F noise
factor (unitless)
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End