The QDC varies with sidereal time as the background cosmic noise is not constant in all directions. An empirical method is used to generate the QDCs. The effect is the same as the visible twinkling of stars due to variations in the atmosphere. Scintillation is readily identified in the data. Scintillation is most easily explained by analogy to a diffraction grating.
Ionospheric irregularities are the equivalent of the diffraction grating.
The received signal is then the sum of signal from multiple paths. As the path lengths change the signal varies due to constructive and destructive interference, hence the star twinkles. Sidereal time Time measured with respect to the stars as opposed to the sun. 56m 4.09053s of mean solar time. The widebeam antenna is a single crossed-dipole antenna.