A detailed description of a Stark‐modulation (see reference 1) microwave spectrograph which has been designed and constructed in this laboratory is given. Circuit diagrams and values of the components are given for all the custom‐built equipment. The frequency range is from 17 to 28 kmc/s.Peak Stark‐modulation voltages up to 1500 volts sine wave and 800 volts square wave are used. The sensitivity is better than 1×10−8cm−1. The absorption lines are about 300 kc wide at half‐power and the practical limit of resolution is between ½ and 1 mc. Frequencies may be measured to better than ±0.08 mc.