The Model 312B measures the amplitude and frequency of signal components from 1 kHz to 18 MHz. It is calibrated to read amplitude in terms of power referenced to commonly used impedances. Frequency components are separated through the use of selectable bandpass filters. The frequency of the measured signal is displayed by a digital LED display. The input can be applied either through a BNC connector or through the 11530A probe. The input circuits of the 312B contain a reference level attenuator that limits the input signal to a level necessary to prevent overloading of the input amplifier. Refer to Paragraphs 3-10 and 3-12 for the procedure for setting the attenuator to prevent overloading and to optimize signal-to-noise ratio. The 312B will make both balanced and unbalanced measurements. These measurements can be made in either terminated or unterminated (bridged) modes. There are seven selectable impedances in the terminated mode; 50 ohms, 60 ohms, 75 ohms, 124 ohms, 135 ohms, 150 ohms, and 600 ohms. When in the bridged mode, the nominal input impedance is 10 kilohms in the unbalanced mode and 20 kilohms in the balanced mode. There are three selectable bandwidths. The 3100 Hz bandwidth is provided for amplitude modulated (AM) and single sideband (SSB) measurements and for ease in tuning. The 1000 Hz bandwidth simplified calculation of noise power per hertz of bandwidth- The 200 Hz bandwidth permits separation of closely spaced signals and precise frequency measurements.