exercices-noise

1.- In the output of an antenna, showing an impedance of 50 Ω, it has been measured a noise power of 2.8 10-15 W. The measurement has been made with a wattmeter with 50 Ω of input impedance and 1 MHz bandwidth. All has been done at ambient temperature (290 K) - What is the noise temperature of the antenna? (Answer: Ta = 202,9 K) - If this antenna receives a power of – 90 dBm, and the receiver directly connected to the antenna has an input impedance of 75 Ω, what is the reflection coefficient? - (Use RFSim) Design a matching circuit to be allocated between the antenna and the receiver in order to transfer all the power received for the antenna to the receiver. (https://www.electroschematics.com/rfsim99-download/) 2.- A device has a NF = 10 dB and a gain G = 0dB . What is the minimum input signal necessary that produces the minimum signal detectable at the output, if: a) BW = 1 MHz b) BW = 1 GHz c) BW =1 KHz (Ans: -133,9 dBm) (mimimum detectable signal → S0 = N0) 3.- Obtain the NF and the gain for both of the following schemes: 4.- The amplifier (dashed line device) of the figure needs a SNR of 15 dB to operate. What is the power of the signal, Si, which has to be captured by the antenna? Ans: Si = -83,4 dBm. Boltzmann constant: k = 1.38·10-23 W/Hz·K-1 Ta = 150 K S i N i 7 m de cable L= 4 dB To = 290 K L= 3 dB To = 290 K BW = 8 MHz SNR min= 15 dB