Will the Receiver Read Zero?
- Connect a room-temperature noise source (290 K) to a receiver with noise bandwidth and a power meter; no transmitted signal
- Thermal motion creates random electrical fluctuations — so no, the receiver does not read zero
- Assumes a matched connection: the receiver accepts the source’s available noise power
Random Fluctuations Carry Real Power
- Noise voltage vs. time: no repeating cycle; mean voltage ≈ 0
- But the squared fluctuations have a positive average: the noise power is real
- Noise density vs. frequency: flat at height over a width of hertz
- The collected “area” is the total noise power
Thermal Noise Density
Thermal Noise
- in W/Hz; = Boltzmann’s constant ( J/K)
- In dB:
- At 290 K:
- Doubling raises the noise density by 3.0 dB
- For a receiving system, becomes the system noise temperature