Carrier current telephony and telegraphy

Repeaters. From the discussion of the transmission characteristics of lines which will be given later in the paper, the very great practical importance of amplifying apparatus at intermediate points on a line employing carrier frequencies will be evident. For this purpose fortunately we have available, first, the vacuum tube, and, second, a large variety of methods of applying this tube which have been developed to a high state of efficiency in connection with the voice frequency telephone repeater. While, as just indicated, the same general considerations apply to repeaters for carrier current circuits as to repeaters on circuits operated at voice frequencies, the conditions peculiar to carrier current operation require that the repeaters for this service differ quite considerably from standard voice frequency repeaters.