2-10 Reception Reception occurs when a transmitted electromagnetic wave passes through the receiver antenna and induces a voltage in the antenna. Selection Selection is the ability of the receiver to select a particular frequency of a station from all other station frequencies appearing at the antenna of the receiver. Detection Detection is the action of separating the low (audio) frequency intelligence from the high (radio) frequency carrier. A detector circuit is used to accomplish this action. Reproduction Reproduction is the action of converting the electrical signals to sound waves, which can then be interpreted by your ear as speech, music, and the like. An example of this might be the stereo speakers in your car. RECEIVER CHARACTERISTICS Sensitivity, noise, selectivity, and fidelity are important receiver characteristics. These characteristics will be useful to you when performing receiver tests. They can help you to determine whether a receiver is working or not or in comparing one receiver to another. Sensitivity The ability of a receiver to reproduce weak signals is a function of the sensitivity of a receiver. The weaker a signal that can be applied to a receiver and still produce a certain value of signal output, the better the sensitivity rating. Sensitivity of a receiver is measured under standardized conditions. It is expressed in terms of the signal voltage, usually in the microvolts that must be applied to the antenna input terminals to give an established level of the output. The output may be an ac or dc voltage measured at the detector output or a power measurement (measured in decibels or watts) at the loudspeaker or headphone terminals. Noise All receivers generate a certain amount of noise, which you must take into account when measuring sensitivity. Receiver noise may originate from the atmosphere (lightning) or from internal components (transistors, tubes). Noise is the limiting factor of sensitivity. You will find sensitivity is the value of input carrier voltage (in microvolts) that must be applied from the signal generator to the receiver input to develop a specified output power. Selectivity Selectivity is the degree of distinction made by the receiver between the desired signal and unwanted signals. You will find the better the ability of the receiver to reject unwanted signals, the better its selectivity. The degree of selection is determined by the sharpness of resonance to which the frequency- determining circuits have been engineered and tuned. You usually measure selectivity by taking a series of sensitivity readings. As you take the readings, you step the input signal along a band of frequencies above and below the circuit resonance of the receiver; for example, 100 kilohertz below to 100 kilohertz