主题：【原创】关于阿波罗登月的各种质疑及相关讨论的专题 -- 随园过客

why is the system noise -188dB?

If we consider the thermal noise only, it will be -131.6dB (if use 210K and 6MHz band width).

However, 17dB S/N ratio is still big enough to distinguish the signal from the noise.

Today, GSM cell phone can even work at lower S/N. The noise power is around -115dBm. If the signal power is -100dBm, we still can hear the speech, but the quality might be bad, e.g., broken speech. Here, the S/N is only 15dBm.Normally the GSM cell phone can work pretty good with -90dBm signal strength, or, S/N = 25 dBm. The GSM cell phone will show full antenna bar when the signal power is around -70dBm (S/N=45dBm). Remember, 17dB is 47dBm. hoho