Noise Limiters, Noise Blankers and Digital Signal Processing

摘要

If radios are our friends, surely noise is our enemy! If we find a channel without interference, the limitation of how well we can hear usually comes down to how much stronger the signal we want to hear is than the noise in the receiver. Noise comes in a number of flavors—the most frequently encountered are: 1. Random or Gaussian noise—this is the background noise that's always there. In the VHF and higher regions of the spectrum, it often is largely generated in the receiver due to random motion of electrons in the circuitry. The internal noise is added to that coming into the antenna from the sun and other extraterrestrial bodies. 2. Impulse noise—this is the noise contribution from individual devices that tend to radiate even though they aren't intended to be radio transmitters. Automobile ignition systems are the classic—every time a spark plug fires, the ignition wiring transmits a wideband signal just like an early radio spark transmitter. Electric motors as in drills, saws and even washing machines sometimes do as well.