Antenna height considerations

The Aspects for Antenna heights considerations are depending upon the wave range and economical reasons. The Aspects for Antenna heights considerations are depending upon the wave range and economical reasons. At VLF, LF and MF the radio mast or tower is often used directly as an antenna. Its height determines the vertical radiation pattern. Masts and towers with heights around a quarter wave or shorter, radiate considerable power towards the sky. This allows only a small area of fade-free reception at night, because the distance at which groundwave and skywave are of comparable strength and can interfere with each other is severely restricted (approximately 40 kilometres to 200 kilometres from the transmission site, depending on frequency and ground conductivity). For high power transmitters, masts with heights of about half the radiated wavelength are preferred because they concentrate the radiated power toward the horizon. This enlarges the distance at which selective fading occurs. However, masts with heights of around half a wavelength are much more expensive than shorter ones and often too expensive for lower power mediumwave stations. For longwave transmitters, however, the construction of halfwave masts is infeasible in most cases, either for economic reasons or because of problems with flight safety. The only radio mast for longwave with a height of half a wavelength built to date was the Warsaw Radio Mast (which did not survive). For frequencies lower than the longwave range, masts have to be electrically enlarged by base loading coils or structures on the top, because the heights required for masts of even a quarter wavelength are too large to realize physically.