Introduction to Space Systems and Spacecraft Design

1
Communications - Decibel Ref SMAD Sections 13
Communications Architecture
Introduction to Space Systems and Spacecraft
Design Space Systems Design
2
Communications - Decibel
Dealing with large and small signal levels
Decibels --? powers of 10
Absolute power
PdB 10Log10 (P2/P1)
Amplifier gain/loss
units - W
units 1 W
units - dbW
PdB(dbW) 10Log10 (P2(W)/1(W)
units - mW
units - dbm
units 1 mW
PdB(dbm) 10Log10 (P2(mW)/1(mW)
Introduction to Space Systems and Spacecraft
Design Space Systems Design
3
Communications - Decibel
Dealing with large and small signal levels
Decibels --? powers of 10
PdB 10Log10 (P2/P1)
PdB(dbW) 10Log10 (P2(W)/1(W)
PdB(dbm) 10Log10 (P2(mW)/1(mW)
3
Introduction to Space Systems and Spacecraft
Design Space Systems Design
4
Communications - Decibel
Dealing with large and small signal levels
Decibels --? powers of 10
Add decibel
Multiply absolute values
4
Introduction to Space Systems and Spacecraft
Design Space Systems Design
5
Communications - Decibel
Dealing with large and small signal levels
Decibels --? powers of 10
Add decibel
Loss is value lt 1.0
Multiply absolute values
5
Introduction to Space Systems and Spacecraft
Design Space Systems Design
6
Communications - Decibel
6
Introduction to Space Systems and Spacecraft
Design Space Systems Design
7
Communications - Decibel
Comparing Power Levels using Decibels
PdB 10Log10 (P2/P1)
When (P2/P1) gt 0 dB is positive
When (P2/P1) lt 0 dB is negative
Let P1 4 watts Let P2 8 watts
P2/P1 2 ratio P(dB) 3 dB
Let P1 8 watts Let P2 4 watts
P2/P1 0.5 ratio P(dB) -3 dB
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Introduction to Space Systems and Spacecraft
Design Space Systems Design
8
Communications - Decibel
Absolute Power Levels using Decibels
PdBm 10Log10 (P(mw)/1mw) reference to 1mw
10Log10 (1mw/1mw) 0dBm
PdBw 10Log10 (P(w)/1w) reference to 1w
10Log10 (8w/1w) 9dBw
Every time it doubles, add 3dB
Every time it is 1/2, subtract 3dB
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Introduction to Space Systems and Spacecraft
Design Space Systems Design
9
Communications - Decibel
Powers greater gt 1 watt
0 dBw 1 watt 3 dBw 2 watts 6 dBw 4
watts 9 dBw 8 watts 10 dBw 10 watts
1 watt x 101 20 dBw 100 watts
1 watt x 102 30 dBw 1000 watts 1 watt x
103 100 dBw 10 M watts 1 watt x 1010
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Introduction to Space Systems and Spacecraft
Design Space Systems Design
10
Communications - Decibel
Powers greater lt 1 watt
0 dBm, 1 milliwatt -3 dBm 0.5
milliwatts -6 dBm 0.25 milliwatts -9 dBm
0.125 milliwatts -10 dBm 0.100 milliwatt 1
milliwatts x 10-1 -20 dBm 0.010 milliwatts 1
milliwatts x 10-2 -30 dBm 0.001 milliwatts
1 milliwatts x 10-3 0.001 milliwatts 1
microwatt
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Introduction to Space Systems and Spacecraft
Design Space Systems Design
11
Communications - Decibel
11
Introduction to Space Systems and Spacecraft
Design Space Systems Design
12
Communications - Decibel
Questions?
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Introduction to Space Systems and Spacecraft
Design Space Systems Design