Icom AH-740 Instruction Manual

Also see for AH-740: Instruction manual

Contents

32INSTALLATIONS2For best communications, position the antenna as high aspossible. The Figure 1 shows the preferred option selection.The Figure 2 shows an antenna installation that uses the op-tional AH-5NV, for best communications on the 30–300km(18.6–186.5 miles) short ranges, and up to 1500 km (932miles) medium ranges.Figure 1Figure 2What is NVIS?NVIS stands for Near Vertical Incidence Skywave.The NVIS radio-wave propagation provides usable signalsbetween groundwave and skywave distances. (between 50and 650 km; 30 and 400 miles) The radio waves from theantenna travel upwards into the ionosphere, and then arerefracted back down in a circular area. The signals can bereceived up to 650 km (400 miles) from the transmitting sta-tion. Refraction fails if the frequency is too high. The signalstrength is reduced if the frequency is too low, because ofabsorption.precautions when the optional AH-5NV is in-Dstalled on a vehicleRWARNING! The NVIS antenna element can swing a lotwhile driving. Therefore, we strongly recommend that you re-move the NVIS antenna while driving. Otherwise the antennaelement may swing excessively and interfere with your driv-ing.