The HP 355B are precision attenuator is useful as a component or laboratory instrument. Specifications. Attenuation: 120 db in 10 db steps. Frequency Range: DC to 500 MC. Overall Accuracy: +/- 0.3 db to 120 db at 1000 cps, +/- 1 db to 60 db below 250 MC, +/- 2 db to 120 db below 500 MC. Impedance: 50 ohms. Maximum SWR: 1.2 below 250 MC, 1.5 below 500 MC. Max. Insertion Loss: 0 at dc; 0.4 db at 60 MC; 1.0 db at 250 MC; 1.5 db at 500 MC. Power Dissipation: 0.5 watts average, 350 v peak.