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Review of the Subject.-In considering methods for in-the effect of codes differing in the number of "currentt values" creasing the speed of telegraph circuits, the engineer is confronted employed. By this is meant the number of diffcrent current values by the problem of transmitting over a circuit the maximum amount which are employed in a system in forming the different charactcrs. of intelligence using a given frequency range, without causing undue To illu-strate, an ordinary land line telegraph circuit mahes use of interference, either in the circuit being considered or fron that two current values, that is, zero current and the current which flows circuit to other circuits.when the battery is connected to the circuit, or it may u.se a cutrrent In this paper the following two fundamentally important factors value in one direction when battery is connected to the ccirCit with in connection with this problem are given principal attention: one polarity and a second current value in the opposite direction of 1. Signal shaping, i. e., giving signals the best wave shape before similar magnitude when the battery is connected to the circuit with impressing them on the transmitting medium so as to be able to send the opposite polarity. Submarine cables, on the other hand, ordinarily employ three different current values, that is, ( definite signal elements at maximum speed without undue interference into other circuts. value in one direction, a similar value int the opposite direction, and zero current. If a quadruplex circuit is analyzed, it will be seen 2.i Chice oftcodegsoeasnomtranmitsthemaximumamountof that there are four different current values employed. There is, of intelligence wihagvnncourse, no theoretical limit to the number of current values wthich mayThese factors are discussed with the idea of indicating the best be thus employed.methods, as well as to give an idea of what may be expected fromThe paper also contains a discussion of certain telegraph systems these methods.which have been advocatedl, and an endeavor is made to clear upIn connection with the choice of codes, consideration is given to various misconceptions relative to the possibilities of these systems.SIGNAL SHAPING suitable networks and waves made up of half cycles of a SEVERAL different wave shapes will be assumed and sine wave, bringing out the inferiority of the latter. comparison will be made between them as to:DIRECT-CURRENT TELEGRAPH TRANSMISSION OVER 1. Excellence of signals delivered at the distant A DISTORTIONLESS LINE end of the circuit, and 2. Interering properties of the signals Before proceeding with this discussion, two terms, Consideration will first be given to the case where which will be used in this paper, and which are condirect-current impulses are transmitted over a distor-sidered to be of fundamental importance, will be tionless line, using a limited range of frequencies. deflned-"signal element" and "line speed." It is Transmission over radio and carrier circuits will next usually possible especially when sending i...

Synopsis: This paper considers two fundamental factors entering into the maximum speed of transmission of intelligence by telegraph. These factors are signal shaping and choice of codes. The first is concerned with the best wave shape to be impressed on the transmitting medium so as to permit of greater speed without undue interference either in the circuit under consideration or in those adjacent, while the latter deals with the choice of codes which will permit of transmitting a maximum amount of intelligence with a given number of signal elements. It is shown that the wave shape depends somewhat on the type of circuit over which intelligence is to be transmitted and that for most cases the optimum wave is neither rectangular nor a half cycle sine wave as is frequently used but a wave of special form produced by sending a simple rectangular wave through a suitable network. The impedances usually associated with telegraph circuits are such as to produce a fair degree of signal shaping when a rectangular voltage wave is impressed. Consideration of the choice of codes show that while it is desirable to use those involving more than two current values, there are limitations which prevent a large number of current values being used. A table of comparisons shows the relative speed efficiencies of various codes proposed. It is shown that no advantages result from the use of a sine wave for telegraph transmission as proposed by Squier and others2 and that their arguments are based on erroneous assumptions.