Spectracom 8194B, Инструкция по эксплуатации

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8194B, 8195B, 8197B Spectracom Corporation
GPS Ageless Master Oscillator Instruction Manual A-2
A.2 GPS qualifying algorithm selection
The Spectracom Master Oscillator is equipped with three selectable GPS qualifying
algorithms. The factory default algorithm is GPS Qualifying Algorithm GQA1. This
algorithm places strict requirements on the received GPS signal. Every second the
GPS signal is qualified and receives a pass/fail quality judgment. Under GQA1,
reception is of passing quality when the receiver is tracking at least four satellites with
signal strengths >40 and a Tracking Mode of 08. This rigid qualifying process is needed
to enable the phase locking algorithm. The phase lock algorithm produces accuracies
of ±1 x 10
-11
on the disciplined oscillator outputs.
In applications where GPS reception is marginal or intermittent, an alternate GPS
qualifying algorithm may be selected. GPS qualifying algorithms GQA2 and GQA3
permit operation while tracking only a single satellite. These algorithms do not require a
minimum signal strength threshold. A satellite is qualified for use whenever its Tracking
Mode is set to 08.
The number of satellites tracked and their current Tracking Model value can be seen
using the GSS command. Refer to Section 4 of this manual for a complete description
of the GSS command.
GPS Qualifying Algorithm GQA3 initially begins similar to GPS Qualifying Algorithm
GQA1. A minimum of four satellites with signal strengths greater than 40, Tracking
Mode of 08 must be tracked and establish a 3D-fix for 1 minute. At this point, the
Tracking GPS lamp will turn on and the qualifying parameters are reduced to tracking
one satellite with a Tracking Mode of 08.
GPS Qualifying Algorithm GQA2 does not require an initial 3D-fix or track more than
one satellite to operate. Select GPS Qualifying Algorithm GQA2 whenever local
interference prevents the receiver from obtaining a 3D-fix. For example, select GQA2
for installations installed in close proximity to TV channels 66 or 23 transmitters.
NOTE:
Selecting GPS Qualifying Algorithm GQA2 or GQA3 changes the oscillator-
disciplining algorithm from phase locking to frequency locking. This reduces
the output accuracy from 1 x 10
-11
to 1 x 10
-10
. This accuracy is sufficient to
meet most transmitter frequency requirements.