GPS Discipline
GPS discipline of the frequency occurs when a positive-going 1pps signal from a GPS such as the
QRP Labs QLG2
is connected to the ProgRock2 module. In this mode,
CLK 2 is set to 9,999,999.5 Hz regardless of the CLK 2 configuration setting, and this frequency is
measured using the 1pps leading edge as a frequency counter gate.
GPS discipline is controlled by the parameters on the configuration screen, as follows:
•
Adjustment:
this is the error of the reference output, expressed in units of 1 / 3650’ths of a
Hz at 9,999,999.5 Hz. This value is loaded at power-up. However when GPS discipline is
applied, the value is internally updated. It is not saved to memory; when you press ‘s’ to
save the configuration, the current live GPS discipline value is copied into the memory
(startup) parameter.
•
GPS threshold:
When in 90-degree and 270-degree phase offset modes, this setting
controls by how many 3650’ths of a Hz at 9,999,999.5 Hz the internally calculated
adjustment parameter must change, since the last time output oscillator clocks are updated,
until the next time output oscillator clocks are updated. When not in phase offset modes,
there is always a very slight adjustment to the output frequencies, at every single 1 second
interval.
•
Cal #1:
this is the minimum step, expressed in units of 1 / 3650’ths of a Hz at 9,999,999.5
Hz, applied at each GPS discipline measurement interval (1 second). You could use a
smaller value, for example, if you have well enclosed ProgRock2 such that any temperature
variations will be slow. Or in some cases, you might wish to increase the value, to cope
faster with sudden extreme temperature variations. The size of the actual step at each
interval is variable; when GPS discipline is initialized, the step is large (2,000) in order to
achieve rapid convergence (calibration); thereafter it is gradually reduced until it hits the
minimum step size. If the GPS discipline algorithm notes rapid drift of the oscillator
frequency, it starts to increase the dynamic step size in order to rapidly correct for the drift.
•
Cal #2:
this controls an additional control loop which acts to keep the cumulative error on
the 9,999,999.5 Hz signal to precisely zero. In other words the average long-term frequency
tends to 9,999,999.5 Hz exactly. The parameter is the additional step size correction, which
is applied on top of Cal #1, at each 1 second measurement interval where the cumulative
error exceeds 0.5 Hz in total since GPS discipline was enabled. Cal #2 can be set to zero if
you do not wish to use this secondary control loop feature.
ProgRock2 manual 1.00b
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