The signal at the input to a balanced twisted pair cable is 10 mW. The cable is 1000 feet long and has an attenuation of 1 dB per 100 feet. This cable is connected to the input of a receiver. The noise level at the input to the receiver is 1 microwatt. What is the signal-to-noise ratio (SNR) (dB) at the receiver input?

Question

Quizplus · Accepted Answer

The signal loses 10 dB over 1000 feet (1 dB per 100 feet). The input signal is 10 mW, which is 10 dBm. After 10 dB attenuation, the signal is 0 dBm (1 mW). The noise level is 1 microwatt (0.001 mW), which is -30 dBm. The SNR is 0 dBm - (-30 dBm) = 30 dB.

The Signal at the Input to a Balanced Twisted Pair