Originally Posted by Digger
Thank you Zyg for the VOACAP plots. I am puzzled by the radiation pattern of the AHR(S)4/4/0.8 - there is nothing at my location and the noise floor is low on 12 MHz - the S-meter sits steadily on S1.
I've attached the pattern for a 12 MHz AHR(S)4/4/0.8 array (source ITU). It has a definite but narrow rear lobe, that explains the good reception in South Korea. The side lobes are close to the main beam and don't send any signal to the rear.
Propagation will also control the path from the lobes and the rear lobe may have a high angle(s) component(s) that can cause local differences in reception, not to mention multipath fading etc.
VOAAREA shows a different coverage each hour for this back end of the beam signal. According to the plots, reception in Japan does improve gradually towards the end of the scheduled transmission at 1000z.
By the way the gain of this antenna is 21.8dBi.
The test transmission may also be running at lower than published power, which would result, of course, in reduced receive levels.