1. A device that gauges frequency distribution of the reflections from different layers in the ionosphere, used in radios.
2. A radio device for determining the distribution of virtual height with frequency, and the critical frequencies of the various "layers" of the ionosphere.

A pulse at a certain frequency is transmitted vertically, and the time for its return is recorded on an oscilloscope; another pulse at a different frequency is then transmitted and timed.

The process is repeated until the entire frequency range of interest, usually from about 1 to 25 MHz, has been explored.

3. A radio device for determining the distribution of virtual height with frequency, and the critical frequencies of the various layers of the ionosphere.