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# A Level Physics Telecom problem watch

1. Hi need help to solve this problem.

A signal of power 2.8 W is applied to a cable of attenuation 6.8dB Km-1 . The constant noise power in the cable is 8.0 micro W and the signal to noise ration must not fall below 35dB. Calculate the maximum length of uninterrupted cable that may be used to transmit the signal.
2. (Original post by jdb23)
Hi need help to solve this problem.

A signal of power 2.8 W is applied to a cable of attenuation 6.8dB Km-1 . The constant noise power in the cable is 8.0 micro W and the signal to noise ration must not fall below 35dB. Calculate the maximum length of uninterrupted cable that may be used to transmit the signal.
If the signal to noise ratio must not fall below 35dB then first calculate the minimum signal power from the 8 microWatt given. The ratio of this minimum signal power to 8 microWatt is 35dB.

When you have this minimum signal power level, find out how many dB that is below the 2.8W starting value.

Then if one km of cable attenuates by 6.8dB you can find how many km is needed to attenuate 2.8W down to the minimum signal level.
3. Thanks a ton, got it how to go about

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