Model 608D VHF Signal Generator furnishes r-f signals from 0. 1 microvolt to 0. 5 volt over the frequency range from 10 to 420 megacycles. The signals may be amplitude-modulated by internally-generated sine waves or by externally-applied sine waves or pulses. The level of the output signal is regulated by an attenuator which is adjusted by a calibrated front-panel control. The attenuator is calibrated in both volts and dbm and can be read directly to an accuracy of ±1 db over the full frequency range when the 608D is terminated in a 50-ohm resistive load. The 608D includes a crystal-controlled heterodyne calibrator which permits the operator to adjust the calibration of the frequency dial at 1-mc and 5-mc check points over the frequency range of the instrument. The Model 608D Signal Generator is designed to meet the exacting requirements of precision laboratory work and yet to be equally useful for general applications in the 10- to 420-megacycle frequency range. The equipment can be used for testing, calibrating, and trouble shooting VHF radio equipment and circuits, and for measuring standing-wave ratios, antenna and transmission line characteristics, receiver sensitivity, etc. To obtain utmost accuracy, particular care has been taken in the design of the 608D to hold spurious modulation to a very low value under all operation conditions.