been lengthened by the same amount. Therefore, we say that the received teletypewriter signal has 9 percent
spacing bias. Conversely, an increase of mark pulse length results in a corresponding decrease of space pulse
length; this is marking bias distortion. The primary causes for bias distortion are improper adjustment of
teletypewriter and terminal equipment as well as distributed constants (inductance, capacitance, and resistance)
in the interconnecting line facilities.
c. Total distortion. Total distortion is the sum of all individual distortions. The total must never exceed 40
percent anything over that value is sure to result in misprinting of the copy. It is the nature of telegraph signals
that as speeds of transmission increase, the percentage of telegraph distortion increases proportionately.
Moreover, the total distortion normally runs higher on radio communication systems than wire systems because
of the noise on the radio transmission path.
d. Monitoring. Misprinting will not occur in a telegraph system until the distortion exceeds a certain value
that depends on the characteristics of the printing equipment. The teletypewriter operator therefore cannot
know when his signal quality is deteriorating until misprinting occurs. It is therefore necessary that the signal
condition be known at all times in an operating system. Each receiving telegraph loop may be monitored with
automatic sensing devices that alert station personnel to the condition of rising telegraph distortion.
e. Causes. There are many causes of telegraph distortion, and many points in the overall system where the
distortion may develop. Every operator and technician in the system must be aware of the possibilities that
exist, and must understand that overall system operation meets satisfactory requirements only when the
telegraph sign in the receive loop comes within the test parameters established for the telegraph carrier
subsystem. The possible causes of telegraph distortion in an integrated communications system include
condition and adjustment of equipment; characteristics of the interconnecting loops, lines, and facilities; and the
condition of the radio transmission path between the two radio sets.
f. Concept. Most of the communication channels in the DCS carry record transmission (teletypewriter).
The message originates and terminates at the opposite ends of the teletypewriter system. The fundamental
concept of the overall integrated communications system therefore involves a realization that all equipments
and devices in the system serve only one purpose-to provide facilities for the receiving teleprinter to reproduce
precisely the same message that was sent out by the distant teletypewriter keyboard.
4. Telephone multiplexing. Each of the individual channels in the FDM telephone carrier terminal operates on
a discrete assigned frequency, as in the telegraph terminal. However, a greater separation of carrier frequencies
is needed to accommodate the increased bandwidth occupied by each telephone conversation, as compared with
the narrow bandwidth of each telegraph carrier channel.