Digital group height measurements of the daytime E-region

Group height measurements for six transmission frequencies (viz. 1.90, 2.00, 2.20, 2.40, 2.60, and 2.80 MHz) were collected at Yarrambat during the months of November and December 1971 and January, February and March 1972. During daylight hours these waves were reflected in the E-region, thus permitting investigation into tidal phenomena in this region. Two three-wire folded half-wave dipoles were used. The echoes were amplified to reduce the effects of absorption on their leading edges, and the overall error in the group height measurements was +- 0.7 km. The semi-diurnal lunar variations in group height were determined and subjected to statistical significance tests. Significance levels lying between 5% and 0.1% were established. The average amplitudes of the variations were for 1.9 MHz: 0.29 km; 2.0 MHz: 0.24 km; 2.2 MHz: 0.28 km; 2.4 MHz: 0.69 km; 2.6 MHz: 0.92 km; 2.8 MHz: 0.78 km, and the average phase of 309.130 indicated that Yarrambat lay north of the focus of the Lsub(Q) current loop system. (author) (author)