Introduction to Space Systems and Spacecraft Design Space Systems 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 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

5. 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

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

7. 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 7 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 8 Introduction to Space Systems and Spacecraft Design Space Systems Design

9. 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 9 Introduction to Space Systems and Spacecraft Design Space Systems Design

10. 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 10 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? 12 Introduction to Space Systems and Spacecraft Design Space Systems Design