Tektronix TG700, Руководство пользователя

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GPS7 GPS Synchronization and Timecode Module
degrade timing accuracy and stability. When evaluating a site, it is important to
monitor it over several days and with a variety of weather conditions present.
This antenna information is not intended to cover all aspects of the antenna system
design. Important topics that were not covered include items like lightening
protection and drip loops. For information about the cable plant design in your
system, contact the appropriate person or group in your organization, or contract
with a quali
fi ed installer.
Figures of Merit (FOM) These numbers are a compendium of the GPS signal quality and the processes that
occur as the instrument progresses through the states needed to lock on to the GPS
signal. The FOM provides a simple scale to evaluate the state of the GPS lock.
The FOM drives the external reference indicator (LED) on the front panel of the
mainframe. When in internal mode, the external LED is off. When in external
mode and the FOM is
≥ 6, the LED is steady green. When the FOM is < 6, the
LED is fl ashing green.
The FOM provides the scale by which you can set the signal warning threshold.
(See page 3-136,
GPO Submenu .)
You can see the description of the FOM in the GPS7 STATUS menu. The
following table lists the fi gures of merit and their descriptions.
Table 3-17: Figures of merit for signal quality
Figure
of merit
(FOM)
Indicator Description
0 No signal This means that no usable satellite signals are
detected. This is normal for a short time after
the signal is applied, but if it lasts more than a
minute or so, then it usually means one of the
following: that there is a problem in the antenna
or cable, the antenna is blocked from direct line
of sight to the satellites, or the power is not
getting to the antenna.
1 Low signal This means that some signal is detected, but
that the signal quality is too low for extraction
of useful timing or position information. This is
a normal situation for a short duration, but if it
persists, the causes are likely to be similar to
those for FOM state 0.
2 Acquire satellites This means that the instrument is receiving data
from the satellites and is determining which
signals to use.
TG700 TV Signal Generator Platform User Manual 3–103