An Automatic Recorder for Measuring the Strength of Radio Signals and Atmospheric Disturbances

A description is given of apparatus for automatically recording the field strength of low-frequency stations and atmospheric disturbances. The receiver, amplifiers, rectifier, and recorder are switched on by relays controlled by a clock and arranged so that for different 5-minute periods during the hour the strength of several stations may be recorded. The sensitivity of the system remains constant over long periods, provided the filament and plate currents do not change. Calibration can be made at any time from either a radio-frequency or audio-frequency source. Typical curves of the variations in signals and atmospheric disturbances are shown.