Spectracom 8194B
10 MHz Reversion
The units we have were originally purchased by Sprint/Nextel
as 8194B-SP323 models. They were factory-modified to produce a GPS-locked 1.25MHz
signal at each of the five BNC output connections, instead of the standard 10
MHz signal. The system still locked a 10 MHz OCXO to the GPS 1 PPS signal, and
then derived the desired 1.25 MHz signal from the accurate 10 MHz signal.
Fortunately for us, it is REALLY simple to revert to production of 10 MHz
outputs.
Follow these steps:
· Remove power and any external cables
connected to the unit.
· Remove the top cover. It should look
like this:
· Remove the power cables from the left
side of the system board.
· Remove the front panel ribbon cable
from the system board.
· Remove the GPS antenna connector from
the GPS receiver.
· Remove the nuts and washers from the
rear panel BNC’s.
· Remove the 10 machine screws securing
the system board to the chassis.
· Carefully remove the system board
from the chassis.
· We will make one change on the system
board. With the GPS receiver on the right side, just to the rear of the GPS
receiver is an unpopulated SMA pad, J20. Immediately to the rear of J20 is a
0-Ohm resistor connecting the center pin of a 3-pin pad to the left position,
labeled “B”. We want to connect that center position to pad “A” instead of pad
“B”, via the 0-Ohm resistor.
· Unsolder the lead from pad “B”, and
solder it to pad “A”.
Before:
After:
· Check your work.
· Reverse the steps above to
re-assemble the unit.
The unit should now produce 10 MHz on all 5 BNC FREQ outputs.
The 1 PPS output remains 1 PPS.
The SMA pad (J20) also has a 10 MHz signal which could be
utilized for an internal distribution amplifier.
Manual Available here,
courtesy of N0ZGO: