Analog Communication Systems. Receivers for CW Modulation In addition to demodulation a receiver must 1. Select the desired signal 2. Reject the other signals 3. Amplify the signal Some of the amplification should occur before demodulation because the. Analog Modulation The purpose of a communication system is to transmit information signals (baseband signals) through a communication channel The term basebandis used to designate the band of frequencies representing the original signal as delivered by the input transducer. • The noise degrades the fidelity in analog communication systems and produces errors in digital communications. • Noise generation limits the weakest transmitted signal. Significant in long-distance communications when the signal attenuation is large. • Signal-to-noise ratio S/N power of the noise power of thesignal S N = Hartley.