Effective Height of Transmitting Antenna in Marchant Ships

Abstract

It is very desirable in antenna designing to know Effective Height of Antenna as correct as possible. Especially, as for distress frequency of 500 KHZ, it is a SOLAS requirement to keep the receivable field strength of 50 μV/m at 280 km apart for main facility and at 190 km apart for auxiliary facility. These correspond to 87.6 dB for main facility and 81.4 dB for auxiliary facility at 1 km apart from ship respectively. As the radiation of transmitter must comply and meet the above requirements, the efficiency of antenna becomes important. However, recently, antenna have been arranged around ship's housing because of convenience of loading and unloarding or maintenance of antenna. Therfore, efficiency of antenna decreases extremely, as the power radiated from antenna is absorbed with ship's strutures such as Radar post, Funnel, etc. By comparing theoretical antenna effective height from actual antenna length (Vertical and horizontal length) and antenna effective height from Radio inspection datas of about 70 ships such as radiated field strength and antenna current and using statistical technic, the Authors decided practical co-efficient as for antenna effective height. In this paper, method of antenna effective height prediction and selection of coefficients are described.