Introduction to Space Systems and Spacecraft Design Space Systems Design

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Introduction to Space Systems and Spacecraft Design Space Systems Design

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Introduction to Space Systems and Spacecraft Design Space Systems Design

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Communications - Decibel

Ref: SMAD Sections – 13 Communications Architecture

Introduction to Space Systems and Spacecraft Design

Space Systems Design

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

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

Communications - Decibel

Dealing with large and small signal levels

Decibels -- powers of 10

Output (dBW) = Input (dBW) + Gain(dB)

Output (W) = Input (W) x Gain

Add decibel

Multiply absolute values

4

Introduction to Space Systems and Spacecraft Design

Space Systems Design

Communications - Decibel

Dealing with large and small signal levels

Decibels -- powers of 10

Output (dBW) = Input (dBW) + (- Loss(dB))

Output (W) = Input (W) x Loss

Add decibel

Component Loss (-Db)

Loss is value < 1.0

Multiply absolute values

5

Introduction to Space Systems and Spacecraft Design

Space Systems Design

Communications - Decibel

6

Introduction to Space Systems and Spacecraft Design

Space Systems Design

Communications - Decibel

P1

P2

Comparing Power Levels using Decibels

PdB = 10Log10 (P2/P1)

When (P2/P1) > 0 dB is positive

Amplifier – gain in power

Attenuation – loss in power

When (P2/P1) < 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

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

8

Introduction to Space Systems and Spacecraft Design

Space Systems Design

Communications - Decibel

Powers greater >= 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

Communications - Decibel

Powers greater <= 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

Communications - Decibel

11

Introduction to Space Systems and Spacecraft Design

Space Systems Design

Communications - Decibel

Questions?

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Introduction to Space Systems and Spacecraft Design

Space Systems Design