Introduction to Space Systems and Spacecraft Design Space Systems Design 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 P dB = 10Log 10 (P 2 /P 1 ) Absolute power P dB (dbW) = 10Log 10 (P 2 (W)/1(W) units - dbW units - W units – 1 W P dB (dbm) = 10Log 10 (P 2 (mW)/1(mW) units - dbm units - mW units – 1 mW Amplifier gain/loss

Introduction to Space Systems and Spacecraft Design Space Systems Design 3 Communications - Decibel Dealing with large and small signal levels Decibels --  powers of 10 P dB = 10Log 10 (P 2 /P 1 ) P dB (dbW) = 10Log 10 (P 2 (W)/1(W) P dB (dbm) = 10Log 10 (P 2 (mW)/1(mW)

Introduction to Space Systems and Spacecraft Design Space Systems Design 4 Communications - Decibel Output (dBW) = Input (dBW) + Gain(dB) Dealing with large and small signal levels Decibels --  powers of 10 Output (W) = Input (W) x Gain Add decibel Multiply absolute values

Component Loss (-Db) Introduction to Space Systems and Spacecraft Design Space Systems Design 5 Communications - Decibel Output (dBW) = Input (dBW) + (- Loss(dB)) Dealing with large and small signal levels Decibels --  powers of 10 Output (W) = Input (W) x Loss Add decibel Multiply absolute values Loss is value < 1.0

Introduction to Space Systems and Spacecraft Design Space Systems Design 6 Communications - Decibel

Introduction to Space Systems and Spacecraft Design Space Systems Design 7 Communications - Decibel P dB = 10Log 10 (P 2 /P 1 ) P1P1 P2P2 Comparing Power Levels using Decibels When (P 2 /P 1 ) > 0 dB is positive When (P 2 /P 1 ) < 0 dB is negative Amplifier – gain in power Let P 1 = 4 watts Let P 2 = 8 watts P 2 /P 1 = 2 ratio P(dB) = 3 dB Let P 1 = 8 watts Let P 2 = 4 watts P 2 /P 1 = 0.5 ratio P(dB) = -3 dB Attenuation – loss in power

Introduction to Space Systems and Spacecraft Design Space Systems Design 8 Communications - Decibel P dBm = 10Log 10 (P(mw)/1mw) reference to 1mw Absolute Power Levels using Decibels P dBw = 10Log 10 (P(w)/1w) reference to 1w = 10Log 10 (1mw/1mw) = 0dBm = 10Log 10 (8w/1w) = 9dBw Every time it doubles, add 3dB Every time it is 1/2, subtract 3dB

Introduction to Space Systems and Spacecraft Design Space Systems Design 9 Communications - Decibel 0 dBw= 1 watt 3 dBw = 2 watts 6 dBw = 4 watts 9 dBw = 8 watts 10 dBw = 10 watts = 1 watt x dBw = 100 watts = 1 watt x dBw = 1000 watts = 1 watt x dBw = 10 M watts = 1 watt x Powers greater >= 1 watt

Introduction to Space Systems and Spacecraft Design Space Systems Design 10 Communications - Decibel 0 dBm,= 1 milliwatt -3 dBm = 0.5 milliwatts -6 dBm = 0.25 milliwatts -9 dBm = milliwatts -10 dBm = milliwatt = 1 milliwatts x dBm = milliwatts = 1 milliwatts x dBm = milliwatts = 1 milliwatts x = milliwatts = 1 microwatt Powers greater <= 1 watt

Introduction to Space Systems and Spacecraft Design Space Systems Design 11 Communications - Decibel

Introduction to Space Systems and Spacecraft Design Space Systems Design 12 Communications - Decibel Questions?