26 097-55501-01 Issue 6 – June 2003
1
TimeHub 5500 System Guide
oscillator. This will be a quality level of 3 for any rubidium type
clock (090-55513-01 and 090-55514-02) (Stratum 2 traceable) and
5 for any quartz type clock (090-55511-01 and 090-55512-02)
(Stratum 3E traceable). This will typically occur in a couple of
situations:
- Following warm-up, the clock card will enter freerun mode
(indicated by front-panel LED) while input references are being
qualified. During this time the internal oscillator on the active
clock card is the active timing reference.
- If, for some reason, all external timing references become dis-
qualified (for example, signal is lost), the TimeHub 5500 will
enter either Freerun or Holdover mode (indicated by front-panel
LED). In either mode, the internal oscillator on the active clock
card becomes the active timing reference. If external timing ref-
erences later become re-qualified, the TimeHub 5500 will
return to normal operation, no longer using the internal oscilla-
tor as the active timing reference.
• It is possible to override the normal behavior for setting of SSM
values on DS1 ESF outputs by using the OMANSSM (Output
Manual SSM) keyword. This provides the capability to select a
specific SSM quality level to be output on a per output card basis.
By enabling OMANSSM (set to "Y") for a particular output card, any
DS1 ESF outputs associated with that card will output the quality
level set via the OQLEVEL (Output Quality Level) keyword. A
primary reason for providing this capability is to allow information
such as "DON'T USE for synchronization" (quality level 8) to be sent
to downstream equipment during maintenance operations.
TL1 commands are used to enable SSM and assign quality levels.
1.3.5 Clock Cards
Clock cards provide input monitoring, selection, and holdover. Two types of
clock cards are available:
• Standard clock cards: These cards are equipped with five inputs
(four DS1 and one 5/10 MHz) and do not support expansion
shelves).
- Five-input with an ST2E rubidium oscillator (090-55513-01)
- Five-input with an ST3E quartz oscillator (090-55511-01)
• Extended capacity clock cards: These cards are equipped with nine
inputs (four DS1, four monitoring inputs, and one 5/10 MHz) and
do support expansion shelves. Please note that if you will have an
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