MANUAL P/N 900000035 REV C
13
6 Calibration
Calibration is only applicable to units fitted with a free running internal OCXO.
The center frequency of the OCXO may be periodically adjusted to compensate
for aging.
1. Remove the top cover of the FDU-240 and put it aside.
2. Identify the internal OCXO and remove the 4 - 40 screw that covers the
calibration access hole.
3. Allow the unit to operate for 24 hours to allow the OCXO to fully stabilize.
4. Connect one of the 10 MHz reference outputs to a frequency counter with
at least an
11 digit resolution.
CAUTION:
The frequency counter MUST be configured to use an external reference
such as a Cesium, Rubidium, or GPS disciplined OCXO as its time-base.
The calibration accuracy of the FDU-240 can only be as accurate as the
reference against which it is calibrated. It should be better than 1x10
-10
5. Using a very small screwdriver, insert it carefully into the OCXO
adjustment access hole until it engages with the slot in the adjustment
potentiometer. Slowly adjust the potentiometer until the frequency counter
reads 10.000000000
±
5 MHz.
