**Could you answer all parts of the question, it\'s not that big, and no nonsens
ID: 1813072 • Letter: #
Question
**Could you answer all parts of the question, it's not that big, and no nonsense answers please ****
A superhet is receiving a signal from an AM modulator where the carrier
signal has an amplitude Ec and carrier frequency fc. The frequency of the information signal is fi
.
The modulator has following parameters.
*output -load- resistance - RT,
* modulation index - m,
* total amplification through the modulator stages - G_T
During the propagation through the air signal power is attenuated by a factor C (C < 1).
a. Calculate the input power received at the receiver.
This should probably be power available to the reciever? Where using modern electronic communications as the subjust textbook (this question is not out of the book though). I have been playing with a standard DSB-FC signal and chcanging that to power and then muliplying by the attenuation. not sure if thats the right approach though.
b. If the intermediate frequency of the receiver is f_IF, what is the maximum RF bandwidth
the device can have if the receiver is not to suffer from image frequency problem.
c. If the RF bandwidth from part b is used and noise density (noise power per Hz) is
N0, calculate the SNR at the input of the receiver.
d. If the total power amplification through the receiver stages is G_R find the output power
of the receiver.
e. If the noise power at the output is identical to the noise power at the input of the
receiver, find the NF for the receiver.
Thanks
Explanation / Answer
Where kT is the noise spectral density at 290K (-174dBm/Hz) BIF is the IF (pre-detection) BW, and FS is the system (not just the front-end) noise figure of the receiver.
Because the RSSI detector is a logarithmic detector, the SNR input-output relationship can be expressed in a closed-form expression, albeit a messy one. An old paper published in the IEEE Transactions on Aerospace and Electronic Systems derived the expression and plotted the SNROUT vs SNRIN curve. The curve in the article is small and doesn't have enough gridlines, but it is possible to evaluate the expression in an Excel spreadsheet and plot it in better detail. The curve appears below, plotted along with a simple SNROUT = SNRIN curve (linear detection) for comparison. Notice the threshold effect. Below the "crossover point" SNR of 3.7dB, the SNR gets worse going through the detector. Above this point, it improves.
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