Section I. GENERAL INFORMATION

TB-9-4931-539-35 Frequency and Time Measurments Manual
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TB 9-4931-539-35

SECTION I

GENERAL INFORMATION

1. Purpose. This information and guidance for personnel who are involved with

frequency and time measurements. This covers frequency and time standardization

information and the present frequency and time capabilities and techniques.

2. Applicability. This bulletin is applicable to all TMDE support activities (TSA),

Army National Guard (ARNG), and Government owned contractor operated facilities

(GOCO), to include the U.S. Army Primary Standards Laboratory (APSL).

3. Definitions

a. Accuracy. The accuracy of a frequency standard is the difference between its

measured frequency and the U.S. Naval Observatory (USNO) time and frequency

standard. Accuracy is usually expressed in parts in 10N.

b. Diurnal shift. Diurnal shift is a phase offset between eat local standard and a

very low frequency (VLF) signal caused by a shift from a daylight propagation path to a

night path. An opposite (approximately) equal phase offset will occur when propagation

changes from a night path to a daylight path.

c. Global Positioning System (GPS). GPS is a worldwide, satellite-based radio

navigation system developed by the U.S. Department of Defense (DOD).

d. Precise frequency. Signifies a frequency (time interval) requirement within 1

part in 10N.

e. Precise time . Signifies a time requirement within 10 ms.

f. Retrace. Retrace describes the ability of a frequency standard to return to an

original frequency after an offset period. For example, the quartz oscillator will retrace

to less than 1 part in 108 of the original frequency within 45 minutes following a 24-hour

off period. Fast warm-up quartz oscillators will achieve a stability of 5 parts in 1010 in

less than 24 hours. However, the frequency must be adjusted to the accuracy needed.

The exact frequency at which high stability oscillators will stabilize after an off period is

not known and may be any value from the original frequency to the retrace specification.

g. Stability. The stability of a frequency standard is its frequency change. Stability

is usually expressed in parts in 10N/day for the time interval of interest.

h. Standards. Signify the reference values of time and time interval. These

standards are determined by astronomical observation and by the operation of atomic

clocks. They are disseminated by the transport of clocks, radio transmission, and other

means.

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