Symmetricom TimeSource 3000, Руководство пользователя

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TimeSource 3000
Description
097-72000-02 Issue 6: October 2003
S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S
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Installations with full view to the sky see 4 satellites 23+ hours a day, seven days a week. It
is relatively easy to filter out multipath signals using multiple satellites and simple voting
schemes. In addition, rooftop antennas are mounted vertically and all signals below the
horizon are obvious multipath interference and can be masked out of the system. With 4
satellites in view, the GPS timing receiver will provide an error-free lock on its location
through an automatic survey function.
With wall/window installations, voting schemes become less effective as the number of
satellites in view drop. Also, wall/window antennas are mounted horizontally and are prone
to seeing multipath signals reflected off nearby structures and the ground. Wall/window
installations also require the manual input of location data, creating the potential for errors
and the need to detect these errors.
The TimeSource has unique algorithms to account for, and defeat, the added multipath
complications and location data entry error possibilities of wall/window antenna
installations. Large amounts of multipath or major errors in location data entry are easier to
identify and are detected over a relatively short period of time. These short-term errors are
normally reported via the TimeSource tracking success rate parameter.
Small amounts of multipath or minor errors in location data entry are difficult to identify
because they mimic a true signal or an expected satellite behavior pattern. Single satellite
reception over limited periods of time complicates the ability for the internal TimeSource
algorithms to filter out these ghost signals and longer periods of time are needed to sort them
out. TFOM tracks and reports these long-term errors.
At time of installation, marginal or unacceptable TFOM readings can indicate the need to
adjust the antenna placement, the mask angle, and/or the location data. Relatively small
changes in the antenna placement can improve the ability of the system to see satellites and
therefore improve performance. The mask angle can be adjusted to block out lower
elevation portions of the sky if there is good visibility at higher elevations, thereby reducing
multipath. Correct location data is very helpful in identifying and tracking satellites.
In addition, a clock may be stable for many weeks, months, or years but could degrade
because of changes in its environment. TFOM is useful in detecting these infrequent subtle
changes including:
• Maturing foliage or seasonal foliage changes
• Installation of new transmitters nearby (i.e. wireless base station)
• New building construction
• Variations in the day-to-day temperature of the CO