ČSN EN IEC 55016-1-4 ed. 4 - Specifikace přístrojů a metod pro měření vysokofrekvenčního rušení a odolnosti – Část 1- 4: Přístroje pro měření vysokofrekvenčního rušení a odolnosti – Antény a zkušební stanoviště pro měření rušení šířeného zářením

3.1.18 null

minimum in signal level resulting from the vector sum of the direct and ground-reflected signals at the receive antenna and with the level being considerably lower than the in-phase sum of these signals Note 1 to entry: The depth of a null is measured from the in-phase sum of the direct and ground reflected signals. A null in the received signal occurs when the antennas are above a ground plane at heights such that the direct and ground reflected signals are in anti-phase, which can result in large uncertainty in the measurement of field strength. A null extends from 90° to 180° out of phase. At 90° the null depth is approximately 6 dB. The depth is compared to the nearest adjacent maximum signal in the swept frequency response (or height scan of one antenna at a fixed frequency). Note 2 to entry: The dip in signal level on boresight for some DRH antennas is sometimes referred to as a null. This definition does not apply to such dips. Note 3 to entry: IEC 60050-726:1982, 726-02-07 defines standing-wave minimum, with synonym node (of a standing wave), as the location in a propagation medium where the vectorial sum of a specified field quantity of two waves creating a standing wave is a minimum.