Signal-to-Noise Ratio (SNR)June 2nd Fact-of-the-Day
Signal and noise can be measured in power, or in rms voltage or current, and the ratio can be expressed in decibels (although, because of the typical difficulty in separating signal and noise for measurement, the ratio in practice most often is actually signal-plus-noise to noise). Very high ratios are desired in high-fidelity sound systems, but more than a half-century ago it was experimentally determined that an average radio listener thought a 40dB ratio was adequate for reception of a typical AM broadcast program. Based on that, a 30dB ratio (10dB worse) was established as the minimum acceptable ratio in AM broadcast receiver tests. More noise is tolerated in radio communication systems where intelligibility is more important than quality. The minimum acceptable ratio in commercial communication systems is generally considered to be 18dB. However, Radio Amateurs often communicate with ratios ranging down to 0dB, where intelligibility tends to become impossible. ©2005 Martek International All rights reserved.
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