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Noise; internal vs external; sources of external noise

Short answer

Noise is unwanted random disturbance that reduces SNR. Internal noise originates inside the receiver (thermal, shot, etc.), can be calculated; external noise comes from outside (atmospheric, cosmic, industrial) and is hard to predict. External sources: lightning (atmospheric), solar radiation, cosmic/galactic noise, man-made noise from motors and ignition.

What is noise? Distinguish between internal and external noise. List various sources of external noise.

Noise

Noise is any unwanted, random electrical disturbance that adds to the desired signal in a communication system and tends to mask it, reducing the signal-to-noise ratio. Example: hiss in a radio, snow on an analog TV picture.

Internal vs external noise

BasisInternal noiseExternal noise
OriginInside the receiver/devicesOutside the receiver
ExamplesThermal, shot, partition, flickerAtmospheric, cosmic, industrial
PredictabilityCan be calculated (e.g. kTBkTB)Hard to predict
ControlLow-noise design, cooling, narrow BBShielding, site choice, directional antenna

Sources of external noise

  1. Atmospheric noise: lightning discharges and other natural electrical disturbances (static); serious below 30 MHz.
  2. Solar noise: radiation from the sun, especially during sunspot activity.
  3. Cosmic (galactic) noise: radiation from distant stars and galaxies, about 8 MHz to 1.5 GHz.
  4. Industrial (man-made) noise: automobile ignition, electric motors, switching equipment, fluorescent lights, welding machines, high-voltage power lines.

✓ Answer checked by Claude Opus 5.5 (high effort)

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