GDP-32
II
INSTRUCTION MANUAL
May 2002 Section 17, Page 26
Mechanical adjustment of the small case GDP-32
II
crystal
After both the receiver and transmitter controller have had power applied for at least 60 minutes,
the following procedure can be used to adjust the mechanical trim on the crystals:
1. Set the 20-turn crystal adjust trim pot on the XMT to its mid point. This provides for the
maximum electrical adjustment range after the mechanical adjustment is made.
2. Set the electrical trim in the GDP-32
II
to its midpoint. To do this, first get into the
Utilities menu and press 4) Synchronize to XMT. Press
Enter
Enter
to get to the Adjust crystal menu. Press
SELECT DN
End
until the beeps change from a
slow to a high repetition rate. This puts you on the outside range of the electronic
adjustment. Now press
Home
SELECT UP
repetitively for 25 counts (beeps). This will put you in
the middle of the adjustment range.
3. Press
Escape
to exit the Utility Program and turn off the receiver in the proper manner.
Cycle the POWER ON/OFF button on the Control I/O Panel to OFF. The red
crystal light will be off.
4. Remove the 12 screws holding down the Front Panel.
5. On the front panel assembly, very carefully disconnect the wide blue ribbon cable and the
multi-colored cable, both of which go to the card cage motherboard. Also, disconnect the
single, black ground wire at the single wire Molex connector.
6. Fold the front panel assembly over toward the left without disconnecting any more
cables. Make sure you have something for the front panel to rest upon on the left-hand
side of the receiver (a stack of books or something similar).
7. The crystal is located to the left of the card cage and along the side of the battery pack, or
on top of the battery pack.
8. Use a flat-bladed screwdriver to carefully remove the adjustment hole screw located in
the middle of the base of the crystal (next to the coaxial output connector).
9. Cycle the POWER ON/OFF button to ON. Wait at least 15 minutes for the crystal to
warm up again.
10. Connect the synchronization cable between the GDP-32
II
and the XMT-32.
11. Set the BATT/PHASE switch on the XMT-32 to PHASE, and observe the motion in the
meter due to the frequency differences between the crystals.
12. Use the plastic trim tool supplied with the GDP-32
II
to adjust the mechanical trim pot
inside the crystal can. Very carefully rotate the pot about 1/4 turn in one direction and
then the other to determine which direction it should be turned to bring the two crystals
into synchronization.
13. Adjust the mechanical trim to stop the motion in the phase meter. This should normally
take less than 1/2 turn in either direction. If more rotation is needed, it could indicate that
you have a faulty crystal in either the GDP-32
II
or the XMT-32.
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