TM 11-6625-1668-12
Figure 3-3. OS206/GGM-15 (V), controls and indicators.
Section II. OPERATING PROCEDURES
3-5. General
This section contains a description of the types of telegraph distortion that the operator may encounter, the
modes of operation, including strap option information and typical operating procedures.
3-6. Types of Distortion
a. The basic types of distortion are marking-bias distortion, spacing-bias distortion, marking-end distortion
and spacing-end distortion. Bias distortion is that which results in the displacement of the space-to-mark
transition. End distortion is that type of distortion which causes the displacement of the relative mark-to-space
transition to the first mark-to-space signal transition (start pulse) with no significant effect on the space-to-mark
transition. End distortion is associated with start-stop signals only. These types of distortion are illustrated in
b. Bias distortion is called marking bias when the transition from space-to-mark occurs early, resulting in
the lengthening of following marking interval. The distortion is called spacing bias when the space-to-mark
transition occurs late and lengthens the preceding space interval. End distortion is called marking end when
the transition from mark-to-space occurs late, resulting in the previous marking interval being lengthened. The
distortion is called spacing end when the mark-to-space transition occurs early and lengthens the following
space interval.
c. Other types of distortion encountered are characteristic distortion, fortuitous distortion, cyclic distortion,
and speed distortion. Characteristic distortion results from electrically long circuits which do not allow the signal
to reach steady-state conditions within 1 bit time. Characteristic distortion may also result from narrow band-
width on carrier circuits. Fortuitous distortion is intermittent and is the random displacement splitting or breakup
of the mark and space elements. It is caused by many factors such as loop battery fluctuations, primary power
fluctuations, radio path fading, etc., and may occur in addition to bias or end distortion. Cyclic distortion is
considered a type of distortion which varies at a predictable rate. For instance, if bias distortion were to be
measured, and a reading of 5%9 were obtained initially, cyclic distortion could cause this reading to advance to
10% and then back down to 56% over a period of time at a fairly constant rate. Speed distortion will result if
the speed of the incoming signal and the speed of the analyzer are not the same. Speed distortion will be
represented as bias and/or end distortion: marking-bias or spacing-end distortion if the incoming signal speed is
faster than the analyzer operating speed; and as spacing-bias or marking-end distortion if the incoming signal
speed is slower than the operating speed. The distortion increases uniformly from bit to bit within a character.
The amount of speed error in percent is one-fifth of the increase in distortion reading from the first transition to
the sixth transition. For example, a 5 percent increase of marking bias from the first to the sixth bit within a
character would indicate that the incoming signal speed is 1 percent fast.
3-6
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