Introduction to Data Communications
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26f. Transients: Impulse Noise, Gain Hits, Dropouts & Phase Hits

Transients are irregular timed impairments. They appear randomly and are very difficult to troubleshoot. There are 4 basic types of Transients:

  1. Impulse Noise
  2. Gain Hits
  3. Dropouts
  4. Phase Hits

i. Impulse Noise

Impulse noise is sharp quick spikes on the signal caused from electromagnetic interference, lightning, sudden power switching, electromechanical switching, etc.. These appear on the telephone line as clicks and pops which are not a problem for voice communication but can appear as a loss of data or even as wrong data bits during data transfers. Impulse noise has a duration of less than 1 mSec and their effect is dissipated within 4 mSec.

ii. Gain Hits

Gain Hits are sudden increase in amplitude that last more than 4 mSec. Telephone company standards allow for no more than 8 gain hits in any 15 minute interval. A gain hit would be heard on a voice conversation as if the volume were turned up for just an instance. Amplitude modulated carriers are particularly sensitive to Gain Hits.

Introduction to Data Communications
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