RECEIVER CHARACTERISTICS

Selection Selection is the ability to distinguish a particular station’s frequency from all other station frequencies appearing at the antenna. Detection Detection is the extraction of the modulation from an rf signal. Circuits that perform this function are called detectors. Different forms of modulation require different detector circuits. Reproduction Reproduction is the action of converting the elec- trical signals to sound waves that can be interpreted by the ear. RECEIVER CHARACTERISTICS Understanding receiver characteristics is manda- tory in determining operational condition and for com- paring receivers. Important receiver characteristics are sensitivity, noise, selectivity, and fidelity. Sensitivity Sensitivity is a measure of receiver’s ability to re- produce very weak signals. The weaker the signal that can be applied and still produce a certain signal-to- noise (S/N) ratio, the better that receiver’s sensitivity rating. Usually, sensitivity is specified as the signal strength in microvolts necessary to cause a S/N ratio of 10 decibels, or 3.16:1. Noise All receivers generate noise. Noise is the limiting factor on the minimum usable signal that the receiver can process and still produce a usable output. Ex- pressed in decibels, it is an indication of the degree to which a circuit deviates from the ideal; a noise figure of 0 decibels is ideal. Selectivity Selectivity is the ability of a receiver to distinguish between a signal at the desired frequency and signals at adjacent frequencies. The better the receiver’s ability to exclude unwanted signals, the better its selectivity. The degree of selectivity is determined by the sharp- ness of resonance to which the frequency determining components (bandpass filters) have been engineered Figure 1-7.—AM superheterodyne receiver and waveforms. 1-8