Automatic equipment is described for measuring the virtual height of the reflecting regions of the ionosphere. The system comprises a transmitter, which scans a wide frequency range some twenty-five times per second, and a receiver which is tuned slowly through the same range. Each time the frequency of the transmitter passes through the pass-band of the receiver, a pulse is produced which is displayed on an oscillograph, together with other pulses produced by waves reflected from the ionosphere. The advantages of this technique are enumerated.The equipment enables a record, covering the range 2–16 Mc/s, to be obtained in a few seconds. The apparatus is fully automatic and produces records as required without manual operation. The equipment has been designed with a view to duplication, is robust and easy to service, and is semi-portable.