Tektronix SPG8000A, User Manual

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SPG8000A User Manual 3
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,
the external LED will be in one of the se states.
Green (Locked). If Genlock signal is locked, or if GPS/PTP is locked with
FOM ≥ FOM_THRESHOLD.
Yellow (Unstable). If Genlock signal is near loss of lock, or if GPS/PTP is
locked with FOM < FOM_THRESHOLD.
Red (Unlocked). If Genlock signal is loss of lock, or if GPS/PTP is
unlocked/missing.
Note : FOM_THRESHOLD is a user adjustable setting.
Internal and External LEDs are both on only when REF is Genlock and there is loss
of lock. This will cause the Internal LED to be GREEN and the External LED to be
RED.
The FOM provides the scale by which you can set the signal warning threshold.
You can see the current status of GPS or GLONASS signal quality using FOM in
the STATUS button menu. Table 1 lists the figures of merit and their descriptions.
Table 1: Figures of merit for GPS and/or GLONASS signal quality (Option GPS only)
Figure of
Merit (FOM)
Indicator Description
0 No signal This means 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 three
problems: 1. There is a problem in the antenna
or cable; or 2. the antenna is blocked from
direct line of sight to the satellites; or 3. power
is not getting to the antenna.
1 Low signal This means 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 1 This means the instrument is receiving data
from the satellites and is determining which
signals to use.
3 Bad position This means the instrument detects that the
stored position is different from the current