A short wave omnidirectional antenna for the 26 Megahertz band provides
line-of-sight broadcasting at comparatively low power to serve local
communities while suppressing sky wave propagation. Sky wave suppression
is achieved by a critically configured reflector above the radiator or by
a co-located second active or parasitic radiator spaced to achieve
sufficient beam tilt to create a null at critical angles, generally from
the horizon to thirty degrees above. This arrangement allows local
broadcasts to be originated at numerous sites despite the narrow extent
of the band (330 kHz) and the narrow (10 kHz) channel width. Among other
possible applications, the antenna supports transmission using the
Digital Radio Mondiale.RTM. (DRM.RTM.) system for COFDM. COFDM technology
can suppress ghosting and most noise, while low emission angle of the
antenna and low intended transmitter power largely prevent interference
between broadcasts at moderate distances.