Abstract: An adaptive gain control amplifier (12) is described in relation to an audio system for adjusting output volume of a loudspeaker (16) automatically in response to an interference signal (21) such as background noise. The amplifier (12) includes a divider circuit (30) which computes the ratio of a time average of a corrupted signal (20, 21) which is a combination of a controlled output signal (20) and the interference (21), to produce a control voltage which controls the gain of the amplifier. To reduce the dynamic range of the quotient of the ratio the divider circuit (30) incorporates a logarithmic ratio circuit. The circuitry of the amplifier includes a "sensing channel" and a "reference channel" for extraction of the above averages of the corrupted signal and controlled output signal, respectively.

Abstract: An electron spin resonance spectrometer is disclosed which includes a sample and a reference arm (16, 18). The sample arm has a circulator (30) for directing radiation to a resonator (22) in which a sample for analysis is deposited and for receiving radiation from the resonator and directing it to a detector (32). The detector detects the microwave radiation from the sample and reference arms (16, 18) to determine a property or properties of said sample. The sample arm (16) and said reference arm (18) are formed as an integrated microwave bridge which includes a divider (14) having a first output portion coupled to an attenuator (20), said attenuator being coupled to said circulator (30) by a microwave transmission line (110). The circulator (30) is coupled to at least one output by a second microwave transmission line (124).