The model 5185 is a wideband voltage preamplifier with a frequency response from DC to 200 MHz and switchable gain settings of x10 (20 dB) or x100 (40 dB). It has a selectable input impedance of 50 ? or 1 M? and a DC offset facility. The 50 ? frequency response extends from DC to 200 MHz with an equivalent input noise of 10 nV/root Hz at 10 kHz. The 1 M? response exceeds 100 MHz, has switch selected AC or DC coupling and an equivalent input noise of 30 nV/root Hz at 10 kHz.