(1) Local-battery. In a local-battery telephone system, each telephone furnishes its own battery power.
The switchboard serves merely as a switching point in the system. This is a simple system used
primarily in forward areas.
(2) Common-battery. In a common-battery telephone system, all telephones draw their battery power
from the switchboard to which the telephones are connected. This is a more refined system used in
c. Local Lines and Trunks. A military local-battery field telephone system usually has rapidly laid insulated
wire or cable for its lines and uses manual central office equipment of sturdy construction. The hand generator
used for signaling provides a greater distance range in ringdown signaling capability than in the common-battery
system. Therefore, the local lines may be longer. A local line usually refers to the wire leading from a
switchboard or central office to a subscriber's telephone, while a trunk refers to the wire connecting two or more
d. Refinements. The common-battery manual telephone system is used most frequently to serve a large
number of telephone users located in a relatively small area. It has numerous refinements, not found in the simple
local-battery systems, which make possible more efficient and rapid handling of large numbers of calls. Because
of these refinements, however, a common-battery central office with its associated lines requires more time for
installation and greater attention to maintenance. Common-battery manual systems are normally used by corps
and higher headquarters.
e. Dial Systems. In dial telephone systems, which are also common-battery, the use of automatic switching
devices eliminates the errors inherent in human operation of a manual telephone switchboard. A dial central
office requires much intricate wiring and complex equipment. Its installation is both time consuming and costly.
It requires great care in maintenance, but when properly maintained it provides more rapid and accurate circuit
switching and traffic capability than is normally possible with a manually operated common-battery switchboard.
f. Flexibility. To provide greater flexibility for military operations, practically all common-battery
switchboards are designed to permit connections with local-battery switchboards and telephones. The larger
local-battery switchboards further enhance this flexibility by allowing for connections to common-battery
switchboards, both manual and dial.
2-5. DC TELEGRAPHY
Dc systems of telegraph transmission fall into two fundamental classes - - neutral and polar. All other
systems of dc telegraph transmission, no matter how complex, are basically variations of neutral or polar systems.
All teletypewriter systems are merely variations of mechanical telegraph systems wherein the de marking and
spacing Signal pulses occur at stated keying rates. Teletypewriter signals are fundamentally telegraph signals
arranged for mechanical transmission and reception. In all discussions to follow, therefore, teletypewriter
operation will be treated as telegraph operation.