This article is from the Shortwave radio FAQ, by Ralph Brandi rbrandi@lucent.com with numerous contributions by others.
The SINPO code is a way of quantifying reception conditions in a five-digit
code, especially for use in reception reports to broadcasters. The code
covers Signal strength, Interference (from other stations), Noise (from
atmospheric conditions), Propagation disturbance (or Fading, in the SINFO
code), and Overall. The code is as follows:
(S)ignal (I)nterference (N)oise (P)ropagation (O)verall 5 excellent 5 none 5 none 5 none 5 excellent 4 good 4 slight 4 slight 4 slight 4 good 3 fair 3 moderate 3 moderate 3 moderate 3 fair 2 poor 2 severe 2 severe 2 severe 2 poor 1 barely aud. 1 extreme 1 extreme 1 extreme 1 unusable
 
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