Communications Homework Questions 1.Convert -6 dBm into mw.Convert -9 dBm into mw 3.

Communications Homework Questions

1.      Convert -6 dBm into mw.

2.      Convert -9 dBm into mw

3.      What is the attenuation that a power signal has suffered if it started as 6V and reached the end of the cable as 2V?

4.      What is the attenuation that a power signal has suffered if it started as 15W and reached the end of the cable as 7W?

5.      What is the signal to noise ratio of a communications system if the signal is 5V and the noise is 5mV (5 x 10^4 V)?

6.      What is the signal to noise ratio of a communications system if the signal is 5W and the noise is 5mW (5 x 10^4 W)?

7.      In all communications systems all the devices and subsystems used add noise to the signals being transmitted through them. THe output power of a receiver in the presence of a signal is 50mW, while the output noise 9i.e. output without a signal presence is 500µW. The signal to noise ratio is?

8.      In a communications system the components have the following properties/

a.      Input transducer / transmitter                 power gain = 0.3

b.      transmission medium                               attenuation = 0.5 dB km

c.      receiver / output transducer                    power gain = 125

Assuming that the transmission medium is 175 km long, calculate the output power from the system for an input power of 20 dBm.

9.      in a communications system the components have the following properties:

a.      Input transducer / transmitter                 power gain = 0.1

b.      transmission medium                               attenuation = 2 dB km

c.      receiver / output transducer                    power gain = 200

10.  Assuming that the transmission medium is 50 km long, calculate the output power from the system for an input power of 10 dBm.

11.  What would the gain of a system be if it’s input was 100 mW, it’s output 10µW and the noise level 1nW?

12.  What would the strength of the output signal from an optical fibre be if the input signal launched into the 1000 m long fibre optic cable was 100 µW and the attenuation of the cable was 3dB/km?

13.  What is the attenuation that a voltage signal has suffered if it’s transmitted value was 8V, it’s received value was 4.5V and the noise value at the receiver was 15mV?

14.  What is the attenuation that a voltage signal has suffered if it’s transmitted value was 4.8W, it’s received value was 1.9W and the noise value at the receiver was 1.2mW?

15.  What is the signal to noise ratio present at the receiver of a system if the transmitted power value 11W, it’s received value is 6.6W and the noise present was 12mW?

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