Lunar Tide in Sporadic E at Brisbane

Abstract

Accurate measurements have been made at Brisbane of the virtual height of reflection of radio echoes from the E region of the ionosphere, using a pulse transmitter operating at 2·28 Mc/s. The recordings were made by using a cathode-ray tube displaying echoes received from virtual heights between 80 and 150 km; black-out modulation of the cathode-ray tube trace was employed so that echoes appeared as gaps in the trace. To avoid the broadening of the gap with increase of echo signal strength, an automatic gain control was used, which kept the peak output within the time interval corresponding to 80?150 km at a fixed level. The gap width then remained fairly constant (about 16 km), and the recorded height showed no dependence on (input) signal strength. A stable triggered oscillator was used to produce height marks at 10 km intervals every 6 min on the cathode-ray display. The oscillator was started at full amplitude by a triggering wave synchronized with the transmitter modulation pulse; there was a constant delay of 0·1 km. A typical record is shown in Plate 1.