How does a signal that reads 20 dB over S9 compare to one that reads S9 on a receiver, assuming a properly calibrated S meter?

Decibels (dB) are a logarithmic unit used to express the ratio of two power levels. In radio frequency power calculations, the rule of thumb is that a 10 dB increase represents a 10-fold (10x) increase in power. To calculate a 20 dB difference, you apply the 10 dB rule twice. Since 10 dB is a factor of 10, another 10 dB is another factor of 10. Therefore, 10 multiplied by 10 equals a 100-fold increase in power. A signal measuring 20 dB over S9 is exactly 100 times more powerful than a signal right at the S9 mark. The distractor '20 times more powerful' is a common error resulting from treating dB as a direct multiplier rather than an exponent.