Log Receiver

a transistor or vacuum-tube radio receiver in which the amplitude response of the intermediate-frequency or video-frequency amplifier is represented by a logarithmic law.

A log receiver makes possible the reception of signals with a dynamic range of up to 100 decibels and a reduction in the effect of certain types of electrical interference. For example, a logarithmic amplitude response may be obtained by connecting a nonlinear element (diode) in parallel with the collector or anode load in each stage of the amplifier or by sequential addition of voltages from each stage of the amplifier at the common load. In the first case the amplitude response will be linear for small input signals (a linear-logarithmic receiver). As the input signal increases, the diode begins to conduct electric current. The internal resistance of the diode decreases, and it shunts the load resistance. The total load resistance changes in such a way that the amplitude at the output of the amplifier is proportional to the logarithm of the amplitude at the input. In the second case an increase of the input signal causes the amplifier stages to leave the linear mode one by one, beginning with the last stage, and the amplitude response will be logarithmic up to the point of transition into the saturated (limiting) mode of operation.