d, but for larger or more specialist antennas seek professional advice. It is well worth investigating the wind loading likely to be encountered and whether the method used for mounting the antenna is adequate. Care should also be taken when planning the installation of an antenna. Sufficient thought put in at the early stages can enable the antenna to be installed easily and safely. There are many considerations: the location of the antenna, the materials to be used, the way in which it is to be installed, advice to be sought, assistance to be sought, etc. In this way as many problems as possible can be addressed before they occur. As antennas are often installed high in the air, it is necessary to be confident that the installation can be undertaken safely, otherwise it is always best to call in professional assistance. Above all do not take any risks. With adequate preparation, the right materials, sufficient planning, the right level of experience, and above all a keen awareness for safety, no problems and accidents should arise. Receivers Radio receivers are very common these days. They are used in a wide variety of applications and in many different forms. The most obvious type of receiver is the domestic broadcast radio. Today most households have a variety of sets, ranging from portable radios up to hi-fi tuners and car radios are also very common. Virtually all new automobiles these days come with a sophisticated radio already fitted. However, they are not the only types of sets to be found in common use. Cellular phones are very common and their use is increasing all the time, and naturally these contain a receiver. Receivers are also needed for the computer wireless local area network communications systems. There is also a wide range of commercial uses of radio receivers. They are used in communications systems ranging from short-range VHF or UHF walkie-talkies to the longer-range systems needed for aircraft of maritime communications PHILIPS Figure 5.1 A typical domestic portable receiver 120 Newnes 