Annex 1
1 Antenna installation
1.1 Frequencies below 30 MHz
It is recommended that, for frequencies below 30 MHz, vertical or loop antennas
be used. A vertical antenna shorter than one-quarter of a wavelength may be
used, with a RF ground system consisting of either buried radial conductors at
least twice the length of the antenna and spaced 30° or less apart, or an equivalent RF ground screen. An inverted
cone type vertical antenna with a similar ground system may also be used with
some advantage.
1.1.1 It is generally accepted that random variations in
polarization of ionospheric waves are such that the vertically polarized
component is, in general, substantially equal to the horizontal component.
1.1.2 The voltage developed at the output of a passive
vertical antenna shorter than one quarter of a wavelength is substantially
dependant on the frequency. Since the impedance of this antenna is capacitively
reactive, the subsequent voltage response in a field-strength measuring
instrument, when connected to a properly terminated transmission line, is
essentially a direct function of frequency, resulting in a simple, relatively
uniform calibration curve.
1.2 Frequencies between 30 MHz and 1 GHz
1.3 Frequencies above 1 GHz
Antennas for field-strength measurements at frequencies above 1 GHz are usually
directional. Their antenna factor (k-factor, see § 1.4) can be
determined with high accuracy. Due to the directional characteristics of the
antennas the influence of the environment on the measurement accuracy is
normally low.
1.4 Antenna factor
2 Receiver
3 Calibration