This tetrode valve was used in an ionosonde pulse amplifier built by UQ Workshop. The pulse of RF was directed upwards to the ionosphere, to be reflected back below a frequency dependent on the ionospheric layers, and to be transmitted thru the ionospheric layers above that frequency. This was used to determine the best frequency to use for skip propogation between a transmitter and receiver using this general area for reflection of radio waves between the two by the ionosphere.