Appendix D: Serial Port and Telnet Commands
External Time Reference Commands
128 | SmartBits 600x/6000x Installation Guide
ETR TFOM [TFOM] – Allows the user to change the threshold for the Time Figure of
Merit (TFOM), by which the firmware determines the GPS/CDMA’s readiness. This
command was added to allow specialized testing even while the ETR is operating in a
degraded state, such as holdover mode.
More specifically, the TFOM command sets the maximum acceptable TFOM; the largest
range by which the reported time differs from GPS/CDMA time. Valid entries for x for the
GPS (NanoSync and HP/Symmetricom 58503) are 3 through 9; although values of 0
through 2 are also allowed for other compatible GPS/CDMA receivers (available on HP/
Symmetricom 59551 GPS; but not available on HP/Symmetricom 58503 (GPS),
NanoSync (GPS), or Praecis Cf (CDMA). Valid entries for x using the CDMA (Praecis
Cf) are 6 through 9. As illustrated in Table D-3 on page 129, the value of x is a power of
10, in nanoseconds. For example, x = 5 indicates an accuracy of no less than 10
5
, or
100000 nanoseconds.
The SmartBits chassis checks the reported value for the TFOM against the limiting value
set by this command when determining if the time is usable. In order to run a GPS- or
CDMA-based SmartBits SYNC operation without a sufficient antenna signal, this value
should be set to the lowest value possible. In most cases, the default value is
recommended. The default value on reset is 3 for GPS and 6 for CDMA.
Note: When a GPS receiver is not actively tracking a GPS satellite, its Time Figure of
Merit is an estimate only, based on measured performance of the internal crystal oscillator.
Similarly, if a CDMA loses reception of the cellular signal, its TFOM is also estimated.
Table D-2. Frequency Figure of Merit Value Descriptions
FFOM Value Definition SmartBits Chassis Notes
0 PLL stabilized, 1 PPS and
10 MHz output within
specification.
Default requirement for GPS Sync
operations.
1 PLL stabilizing (transient state)
2 PLL unlocked (in holdover
mode)
Allowable state, for a short period
after antenna signal is disrupted.
Both the 1 PPS and 10 MHz signals
are generated, but may not be as
accurate.
3 PLL unlocked (not in
holdover mode). The 1 PPS
and 10 MHz output should
not be considered stable or
usable.
Should not be used for SmartBits
chassis.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
To Next Page
Loading...