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Symmetricom, Inc.
bc620/627AT Time and Frequency Processor
7-1
CHAPTER SEVEN
ADJUSTMENTS
7.0 GENERAL
There are only two adjustments on the bc620/627AT module, RV1 and RV2. (See figure 1-1 for
the location of these potentiometers.)
7.1 TIME CODE PHASE LOCK LOOP ADJUSTMENT
RV2 adjusts the center frequency of the VCO which locks to the carrier of a modulated input
time code. This adjustment is made at the factory and rarely needs adjustment by the customer.
This adjustment can be verified and adjusted correctly using a dual trace oscilloscope and a time
code input.
•
Set the bc620/627AT to Mode 0 (Packet “A”) and select the appropriate time code format
and modulation type (Packet “H”).
•
Connect channel #1 of the oscilloscope to pin #16 of U19 (XR2212). Connect channel #2 of
the oscilloscope to the modulated input time code. Trigger the oscilloscope on the channel
#1 input.
•
Adjust RV2 so that the positive transition of the TTL signal input to channel #1 is centered
on the positive crest of the input sine wave. The negative TTL transition should be centered
on the most negative part of the input sine wave. See Figure 7-1 below.
Figure 7-1
Phase Lock Loop Adjustment
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