jj ii communications (xe37zkt), part i...
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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JJ II
J I
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Fundamentals ofCommunications
(XE37ZKT), Part I
Superheterodyne, OFDM
Josef Dobes
8th
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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JJ II
J I
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1. Outline
• The Simplest AM Crystal Radio
– Peak Detector
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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1. Outline
• The Simplest AM Crystal Radio
– Peak Detector
• Superheterodyne With Single Conversion
– Fundamental Structure of the Superhet
– Mixing Process
– Image Frequency
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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1. Outline
• The Simplest AM Crystal Radio
– Peak Detector
• Superheterodyne With Single Conversion
– Fundamental Structure of the Superhet
– Mixing Process
– Image Frequency
• Downconverting or Upconverting
– Downconverting Example
– Upconverting Example
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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JJ II
J I
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1. Outline
• The Simplest AM Crystal Radio
– Peak Detector
• Superheterodyne With Single Conversion
– Fundamental Structure of the Superhet
– Mixing Process
– Image Frequency
• Downconverting or Upconverting
– Downconverting Example
– Upconverting Example
• Superhet With Dual Conversion
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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• OFDM Fundamentals
– Brick Wall Effect
– Multi Path Reception
– Typical Transmission Parameters
– Signal Spectrum in Adjacent Channels
– Multi Carrier System
– 64-QAM Used for One Carrier (Gray Code)
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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2. The Simplest AM Crystal Radio
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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2. The Simplest AM Crystal Radio
A principle of the demodulation using the peak detector:
1
1Heriot-Watt University, Edinburgh
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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3. Superheterodyne (Superhet) With Sin-gle Conversion
The diagram of the single conversion superheterodyne is the follow-ing:2
2J.P. Silver (www.rfic.co.uk), Superheterodyne Receiver Tutorial
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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The frequencies produced in the superhet as a result of the mixingprocess (ωRF – RF Signal, ωLO – Local Oscillator):
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Superheterodyne . . .
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Superhet With Dual . . .
OFDM Fundamentals
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However, unwanted signals at the RF image frequency being addedto the IF and could increase the noise figure:
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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4. Downconverting or Upconverting
Example: A terrestrial TV tuning receiver is designed to cover theRF frequency range of 45 to 860 MHz, with channel spacings of 8 MHzand an IF of 40 MHz. Assess the downconverting or upconvertingreceiver solutions relating to potential problems with the image fre-quency band.
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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4. Downconverting or Upconverting
Example: A terrestrial TV tuning receiver is designed to cover theRF frequency range of 45 to 860 MHz, with channel spacings of 8 MHzand an IF of 40 MHz. Assess the downconverting or upconvertingreceiver solutions relating to potential problems with the image fre-quency band.
Downconverting: The local oscillator minimum and maximumfrequencies are given by the range and specified IF, i.e.
fLOmin= fRFmin
+ fIF = 45 MHz + 40 MHz = 85 MHz,
fLOmax = fRFmax + fIF = 860 MHz + 40 MHz = 900 MHz.
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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4. Downconverting or Upconverting
Example: A terrestrial TV tuning receiver is designed to cover theRF frequency range of 45 to 860 MHz, with channel spacings of 8 MHzand an IF of 40 MHz. Assess the downconverting or upconvertingreceiver solutions relating to potential problems with the image fre-quency band.
Downconverting: The local oscillator minimum and maximumfrequencies are given by the range and specified IF, i.e.
fLOmin= fRFmin
+ fIF = 45 MHz + 40 MHz = 85 MHz,
fLOmax = fRFmax + fIF = 860 MHz + 40 MHz = 900 MHz.
Therefore, the resulting frequencies of the images are:
fIMmin= fLOmin
+ fIF = 85 MHz + 40 MHz = 125 MHz,
fIMmax = fLOmax + fIF = 900 MHz + 40 MHz = 940 MHz.
The location of images is problematic – see the diagram.
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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Upconverting: A better way consists in choosing a greater IF.Lets pick an IF frequency of say 1.5 GHz. The required LO will nowbe (the LO is below the IF now):3
fLOmin= fIF − fRFmax = 1500 MHz − 860 MHz = 640 MHz,
fLOmax = fIF − fRFmin= 1500 MHz − 45 MHz = 1455 MHz.
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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Upconverting: A better way consists in choosing a greater IF.Lets pick an IF frequency of say 1.5 GHz. The required LO will nowbe (the LO is below the IF now):3
fLOmin= fIF − fRFmax = 1500 MHz − 860 MHz = 640 MHz,
fLOmax = fIF − fRFmin= 1500 MHz − 45 MHz = 1455 MHz.
Therefore, the resulting frequencies of the images are
fIMmin= fLOmin
+ fIF = 640 MHz + 1500 MHz = 2140 MHz,
fIMmax = fLOmax + fIF = 1455 MHz + 1500 MHz = 2955 MHz,
which is not problematic now because the image band does not inter-sect the signal band – see the diagram again.
Outline
The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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Upconverting: A better way consists in choosing a greater IF.Lets pick an IF frequency of say 1.5 GHz. The required LO will nowbe (the LO is below the IF now):3
fLOmin= fIF − fRFmax = 1500 MHz − 860 MHz = 640 MHz,
fLOmax = fIF − fRFmin= 1500 MHz − 45 MHz = 1455 MHz.
Therefore, the resulting frequencies of the images are
fIMmin= fLOmin
+ fIF = 640 MHz + 1500 MHz = 2140 MHz,
fIMmax = fLOmax + fIF = 1455 MHz + 1500 MHz = 2955 MHz,
which is not problematic now because the image band does not inter-sect the signal band – see the diagram again.
As shown, the greater IF causes the suppression of the images. How-ever, the most selective filters can only be realized for lower frequen-cies. As a result, a superheterodyne with dual conversion can beconsidered an optimal solution – see the superhet with the dual con-version.
3J.P. Silver (www.rfic.co.uk), Superheterodyne Receiver Tutorial
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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5. Superhet With Dual Conversion
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The Simplest AM . . .
Superheterodyne . . .
Downconverting or . . .
Superhet With Dual . . .
OFDM Fundamentals
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6. OFDM Fundamentals
Brick Wall Effect4
4ntl:broadcast
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The Simplest AM . . .
Superheterodyne . . .
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OFDM Fundamentals
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Multi Path Reception
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Typical Transmission Parameters
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Signal Spectrum in Adjacent Channels
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OFDM Fundamentals
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Multi Carrier System5
5http://www.DSPeC.org
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The Simplest AM . . .
Superheterodyne . . .
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Superhet With Dual . . .
OFDM Fundamentals
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64-QAM Used for One Carrier (Gray Code)