112 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



portable telephone and compares favourably in this respect with the low-priced test 

 sets. Its advantages, however, are almost wholly those of weight and price, but both 

 are so considerably in its favour that it has a very wide application in specialized forest 

 protection. 



The disadvantages 'of this set are as follows: 



(1) It cannot be used to call a statio-n equipped with the standard instruments, 

 unless an auxiliary signalling device is installed. 



( ; 2) It has no protective equipment and cannot safely be left connected to a line 

 when not in use. 



(3) No means are provided by which a station equipped only with this set can 

 receive a call. Auxiliary apparatus must be available. 



2? CHARACTERISTICS OF THE 1004^ A SET 



The weight of the set is 2' pounds and the length over -all is 9-| in. This set 

 eliminates entirely the heavy, alternating-current generator needed for ringing the 

 ordinary type of polarized bell by substituting an entirely different system of signalling, 

 and thereby greatly reduces the necessary weight. Transmitter and receiver are the 

 same as with the portable telephone and a larger, three-cell, cylindrical, flash-light 

 battery is employed. A switch with two push-buttons is provided. One of these is 

 pressed for signalling, the other while talking and listening. The novel feature of this 

 set is the induction coil, which, besides serving the usual purpose in speech transmis- 

 sion, also serves to produce a very rapidly alternating current, used in signalling in 

 place of the generator and bells. This is accomplished 'by equipping the coil with a 

 vibrator which makes and breaks a contact in the primary of the induction coil. 



The whole apparatus is inclosed in a special aluminium case and equipped with 

 two binding-posts at one end for connection to the line and ground. The proper 

 connections are designated L and G, respectively, on the sides of the instrument near 

 the binding-posts, and it is important that the line and ground wires be attached to 

 the right posts, as otherwise the efficiency of signalling is reduced. 



Calls are made by a system* of long and short buzzes. These are produced by 

 depressing the button marked " 'Signal." After signalling, the " Talk " button is 

 depressed to use the instrument for conversation. Long conversations with the portable 

 must be avoided as the longer the conversation, the greater the drain on the battery. 

 The batteries should last with ordinary usage six or eight weeks and care should be 

 taken to see that fresh ones are secured for renewals. The Ever Ready Tungsten No. 

 705 is the type employed. When inserting a new battery in the battery chamber it is 

 necessary to put the top of the battery in first, so that the spring of the battery chamber 

 cap has the broad surface of the bottom to bear on. 



The signals from this set are received by a howler. The installation of this 

 apparatus has been described in Section 7'6. The instrument itself is described in 

 Section 86. The presence of a number of howlers on the line is objectionable for not 

 only do they produce a disagreeable noise when a signal is sent in either by generator 

 or vibrator, but all conversation on the line is audible in any room where a howler is 

 placed. Howlers should be installed only at the principal switching centres or at such 

 stations ,as are most continuously occupied. Ordinarily they should be at least 30 

 miles apart and may be at greater distances. Any station not equipped with a howler 

 may be called with the usual bell signals through one of these switching centres. 



In using the Adams hand set it is necessary to keep in mind that it is entirely 

 unprovided with a protector and, also, that when it is connected to the line it acts as 

 a direct ground. It should, therefore, not be left connected to any line when not in 

 use, as it would not only be exposed to serious injury from lightning but would prevent 

 other stations from ringing past it. It should also be noted that the sound of the 

 vibrator when received in an ordinary receiver over lines of ordinary length is not 



