Operating instructions

22
To compensate for crystal ageing and other component parameters that drift over time,
the following procedure should be performed approximately once per year.
If your exciter is fitted with the external reference option (an extra BNC connector on
the rear panel), the user can connect an external reference directly to the rear BNC
connector. If the exciter does not have this option, then the top cover of the exciter
should be removed and an external reference oscillator should be connected via a 50
ohm probe to J4 (just to the right of the DC voltage regulators and converters).
The external reference clock, should have a power level from +6 to +26dBm and any
frequency that meets the following criteria:
500kHz, or any multiple, or,
any multiple of 128KHz, greater than or equal to 512kHz, or,
any multiple of 160KHz, greater than or equal to 480kHz.
The frequency should be 10MHz or less in Rev 4 or older versions. In Rev 5, and later
versions the frequency can be as high as 24MHz, and at power levels as low as 0dBm.
No User input is required, except to hit the Enter key when the external reference is
connected. The firmware will automatically adjust both reference oscillators, and save
the new DAC adjustments in FLASH (as parameters) to be used to centre the oscillators
each time the unit powers up.
The user should see the following output. (Note that the temperatures, frequencies,
error values, serial number, etc, indicated are examples only)
Connect an external reference input or the clock output
from a GPS receiver to the GPS input.
Enter <RET> when this has been done.
External Reference is 10.0MHz
Ensure that the displayed reference frequency (10.0MHz in the above example) is the
same as the frequency of your oscillator.
Waiting for a GPS clock.
. . . . . .
The system waits here for a GPS reference to be seen. At this stage, this method of
calibrating the clocks has not been validated by RFT Engineering, so do not attempt to
use this option.
Then the firmware continues.
Have not observed a GPS clock
System Frequency relative to external clock is 7372654.32
The crystal temperature is 32C.
Waiting up to 1 minute for clocks to stabilise.
. . . . . .
The crystal temperature is 32 C
The channel ref error = 1 cnts or, 1.63 Hz
The mod ref error = 1 cnts or, 1.63Hz
The user may see the following error message.
The Model Name is T50_REV4
and the Serial Number is RT11500
Please take note of the Model, DAC values, serial number and
crystal temperature, and report this problem to RFT Engineering.