IT 327 - Schweber Chap 3 1

Thought of the DayMen and women who turn their lives over to God will

discover that He can make a lot more out of their lives than they can. He will: 1. deepen their joys,2. expand their vision, 3. quicken their minds,4. strengthen their muscles, 5. lift their spirits, 6. multiply their blessings,7. increase their opportunities,8. comfort their souls, 9. raise up friends, 10.and pour out peace.

Whosoever will lose his life in the service of God will find he has eternal life.

- Pres. Ezra Taft Benson

IT 327 - Schweber Chap 3 2

Schweber, Chap 3:DeciBels and Noise

IT 327 - Schweber Chap 3 3

1

Just a little tickler

IT 327 - Schweber Chap 3 4

DeciBels

• Origin of the unit?

• Why?

For Power: dB = 10 log10 (P2/P1) For Voltage: dB = 20 log10 (V2/V1)

OR: For Power: dB = 10 log10 (Pout/Pin) For Voltage: dB = 20 log10 (VMeas/VRef)

Example 1: Perfect wire (R = 0Ω; L = 0H; C = 0F)

P1 = 1W; P2 = 1W. Find dB.

IT 327 - Schweber Chap 3 5

DeciBels: More Examples

P1 = 1W; P2 = 0.5W. Find dB.

V1 = 10V; V2 = 5V. Find dB.

P1 = 50W; P2 = 0.1aW. Find dB.

Voyager 1 & 2

P1 = 1W; P2 = 1000W. Find dB.

Commercial power amplifier

P1 = 50kW; P2 = 10µW. Find dB.

Commercial AM radio (KSL 1160)

IT 327 - Schweber Chap 3 6

DeciBels: Standard References

dBW = 1 W How much is 20 dBW?

dBm = 1 mW How much is -30 dBm?

dBV = 1 V How much is 40 dBV?

dBmV = 1 mV How much is -120 dBmV?

dBc = ideal carrier

dBi = isotropic (omnidirectional)

dB (audio) = ? How much is 30 dB? 70 dB? 100 dB? 120 dB?

IT 327 - Schweber Chap 3 7

Noise in Systems

IT 327 - Schweber Chap 3 8

Definition of BW

IT 327 - Schweber Chap 3 9

Definition of BW

IT 327 - Schweber Chap 3 10

Acceptible SNR

• Audio: 90 dB (Classical); 40 dB (other)

• Video: 60 dB

• Digital: 20 dB

• Space: -60 dB