Abstract :
In considering methods for increasing the speed of telegraph circuits, the engineer is confronted by the problem of transmitting over a circuit the maximum amount of intelligence using a given frequency range, without causing undue interference, either in the circuit being considered or from that circuit to other circuits. In this paper the following two fundamentally important factors in connection with this problem are given principal attention: 1. Signal shaping, i. e., giving signals the best wave shape before impressing them on the transmitting medium so as to be able to send signal elements at maximum speed without undue interference into other circuits. 2. Choice of codes so as to transmit the maximum amount of intelligence with a given number of signal elements. These factors are discussed with the idea of indicating the best methods, as well as to give an idea of what ay be expected from these methods. In connection with the choice of codes, consideration is given to the effect of codes differing in the number of “current values” employed. By this is meant the number of different current values which are employed in a system in forming the different characters. To illustrate, an ordinary land line telegraph circuit makes use of two current values — that is, zero current and the current which flows when the battery is connected to the circuit, or it may use a current value in one direction when battery is connected to the circuit with one polarity and a second current value in the opposite direction of similar magnitude when the battery is connected to the circuit with the opposite polarity. Submarine cables, on the other hand, ordinarily employ three different current values, that is, a definite value in one direction, a similar value in Ike opposite direction, and zero current. If a quadruplex circuit is analyzed, it will be seen that there are four different current values employed. There is, of course, no theoretical limit to the- number of current values which may be thus employed. The paper also contains a discussion of certain telegraph systems which have been advocated, and an endeavor is made to clear up various misconceptions relative to the possibilities of these systems
