Question 6 (a) A radio frequency (r.f.) amplifier has a gain of 12 dB and a noise factor of 10. Calculate the value

[answerhappygod]

Question 6
(a) A radio
frequency (r.f.) amplifier has a gain of 12 dB and a noise
factor of 10. Calculate the value of the noise power in dBm
and mW at the output of the amplifier if the signal power and the
noise power at the input is 10 dBm and - 3 dBm
respectively.
(8 marks)
(b) A
pre-amplifier is to be used with the r.f. amplifier in (a). A
10 m length of cable is used to connect the pre-amplifier to
the r.f. amplifier. The pre-amplifier has a gain of
10 dB and a Noise Factor 2. The cable has a loss
characteristic of 0.8 dB/m.
(i) Sketch a block diagram of the
overall system with appropriate justification. Your diagram should
indicate the gain of each block in dB.
(4 marks)
(ii) If the signal level presented to the
pre-amplifier is -30 dBm, determine the level of the signal
power at the output of the amplifier with appropriate
justification.
Your answer should be expressed in dBm and in mW.
(4 marks)
(iii) Determine the effective overall Noise
Factor of the whole system using the information given above with
appropriate justification. Your answer should include an
update of the block diagram of (i) that includes the Noise Figure
for each block.
(6 marks)
(iv) Hence determine the effective SNR at the
output of the amplifier. Assume that the SNR at the input to
the whole system is 20.

Your answer should include an equation showing the relationship
between the Signal-to-Noise Ratio (SNR) and Noise Factor as well as
all working with appropriate justification.
(3 marks)