Aerials for Portables

Radio Record, Volume III, Issue 20, 29 November 1929, Page 26

Aerials for Portables

Lemnetmeenmnedl Preferable to Loops HE use of a loop antenna for portable receivers is réstricted to the larger type set. It is necessary when using smaller receivers, and it is advisable when using larger receivers that are stationed ‘in one place for some time, to erect an improvised aerial. The most popular temporary aerial fox outdoor use is a length of insulated wire thrown over the branch of a tree. It is one of the simplest to erect as a tree with a suitable branch is not very difficult to find, There are occasions, however, when trees are not available, and in these cases it is usually possible to find some high structure in which to suspend the aerial. Get it up as high as possible and let both ends hang freely. Make certain that. the end distant from the set is not contacting with any conductor otherwise a leakage will oceur and the benefit of the aerial be Jost. For the tree supported aerial a length Of insulated wire 80 to 50 feet will be required. This takes up very much less room than the 100 feet, and it is usually very difficult to get an aerial 50 feet high. Heavily insulated wire has very great advantages from the point of view of insulation, but it is difficult to carry. A roll of 24 or 26 double cotton-covered wire with a piece of rubber-covered flex in the middle forms quite an effective aerial wire. The advantage of this is that it may be carried conveniently in any small receiver, The end of this should be secured to an ordinary big reel so that this can act as a weight to carry the wire over its support. The reel should be provided with a screw for a handle and a pencil or stick through the hole to form a winding axis. Once over the branch the wire is so arranged that only the piece of rubbercovered flex touches the tree. The aerial wire is easily wound up again if held by the axis. In a few isolated places it is not possible to find a tree or high structure. In cases such as these a kite aerial may be used, Unless one is experienced in flying kites it is better ta use a moderately-sized high-flying one of the aeroplane type, making the aerial wire only a portion of the total length of the kite line. Two or three hundred feet of strong cord will be required and to the end of this attach 100 feet of strong wire such as 20 gauge enamel or electron wire. The kite should be flown so that the aerial wire is suspended in the air as nearly vertical as possible. Once the kite is flying properly the aerial wire should be anchored by means of an insulator aitached to a stake in the ground, leaving a few feet free to attach to the receiver. An ordinary wire fence may be used as an aerial, but a variable condenser should be interposed between it and the set. Another form of aerial reception is by using two earths. This consists of two earth contacts spaced some thirty to forty feet apart connected by. wires to the receiver, Signals are then picked up from ‘the earth waves and a careful choice of position often results in very good recep-

- "var --_ tion. Two sets of earth spikes will be required together with some 40 or 50 feet. of insulated wire. -.Ordinary 22 or 24 d.cae. wire will do. The earth connection will be the same whatever form the aerial may take and the easiest system is to lay a length of insulated wire underneath the aerial. This acts as a kind of counterpose earth and gives very good results, certainly better than those ob‘tained by a poor earth contact. A contact which is less bulky for transport is an earth spike. The handiest is a piece of thin copper or brass rod. A piece the length of a stair rod will be about right. A short lead should be soldered. to one end and a terminal head should be soldered or screwed into position so as to make insertion or withdrawal easy. Other convenient earths are a piece of neétting laid on the ground or thrown, into a stream. A spike driven into a free is very effective. Elaborate aerials and earths should not be used, but there is no reason why an efficient system should not be improvised. If you cannot get good results examine first this part of the outfit, for it is likely that a change of position of either aeiial or earth may make all the difference.