The system signal-to-noise ratio referred to a receiver input terminals is 20 dB
ID: 2266077 • Letter: T
Question
The system signal-to-noise ratio referred to a receiver input terminals is 20 dB in Problems 1 through 4. The IF bandwidth may assume any minimum value required for the different modulation methods.
1. Determine the detected output S/N ratio (in dB) for an SSB receiver.
(a) 20 (b) 23 (c) 100 (d) 10
2. Determine the detected output S/N ratio (in dB) for an AM receiver with 100% modulation.
(a) 21.8 (b) 15.2 (c) 18.2 (d) 20
Explanation / Answer
1. A single sideband AM signal has only one side band and hence the demodulator will translate the RF signal to baseband
SNR output = SNR input = 20 db
2) SNR output = (m2/(2+m2))(SNRinput)
When m = 100% m = 1
SNRinput = 20 db = 10^2 = 100
SNRoutput = 1/3 x 100 =33.33
Hence SNR output db = 10log33.33 = 15.23