Procedure for swapping the TrueTime GPS receiver in the radon hut:
==================================================================

[last performed Aug.31, 1999, ~noon Japan Time]

1. Preparation:
  1.1. Stop the radon system: Just push STOP button
       - takes approx. 1-2 minutes to fully slow down to a halt
  1.2. To reduce the annoying noises from the fans:
       a) unplug the 2 white box fans (at heat exchqanger and on the
          right side of the control panel) and
       b) turn off the fan tray underneath the GPS receiver.
2. Turn off the (old) TrueTime GPS receiver
   (power button on front panel, right).
3. Disconnect all 4 cables from the receiver at the rear side:
   a) AC plug
   b) optical fiber (orange jacket)
   c) Antenna coax cable (with shrinkwrap around BNC connector)
   d) "1PPS" test coax cable (without shrinkwrap)
4. Slide out the TrueTime box carefully.
   Watch the Motorola (backup) GPS receiver, currently just sitting on top
   of the TrueTime box, not to fall down or unplug mistakenly.  Best if
   you slide out the TrueTime just halfway, move the Motorola down and place
   it on the (now switched-off) fantray below - and then you can slide out
   the TrueTime completely.
5. Take the dustcap of the "Fiber Out" connector of the new TrueTime box and
   place it on the "fiber out" connector of the old box (to protect the
   fiber socket from getting dirty during transport).
6. Slide the new TrueTime into the rack.
   - Again, carefully watch for the Motorola box - and place it on top of
     the TrueTime box again, when halfway back into the crate...
7. Plug in all 4 cables again:
   a) optical fiber (orange jacket) - might need to try turning up to 180
      deg. left or right until it slips in - don't force.
   b) Antenna coax cable (with shrinkwrap around BNC connector)
   c) "1PPS" test coax cable (without shrinkwrap)
   d) AC plug
8. Flip power switch of new TrueTime to ON.
   - initialization messages should appear on the LCD display such as
     "TRUETIME Mk III sys ver [...]" etc.  If you only see black boxes
     or a blank field, turn the "viewing angle" knob somewhat left or right
     until you can see numbers and letters.
9. Configuration via the keypad control keys:
   To enter a configuration function in general, push the FUNC/ENTER key,
   then the function number.
  9.1. Enter FUNC/ENTER, then 5 and 1 (Function 51: Antenna Cable Delay):
       should be set to 60 nsec.  Use cursor keys if corrections needed.
       When ready press FUNC/ENTER again.
  9.2. Enter FUNC/ENTER, then 6 and 9 (Function 69: Set Time Mode):
       should be set to "UTC".  Use cursor keys if not selected yet, until
       UTC appears.  When ready, press FUNC/ENTER again.
  9.3. Enter FUNC/ENTER, then 5 and 3 (Function 53: Set operational mode):
       Select AUTO via cursor, then enter FUNC/ENTER again.
       - Soon after invoking the AUTO mode, the Status LED will turn to red
         for a couple of minutes, and the receiver's memory will be cleared.
       - You might see a message such as "No usable satellites yet" or
         similar for a minute or two.
       - After a short while (within less than 5 minutes usually) you should
         see the first indication of a satellite data lock, which appears
         on the display as "MODE: AUTO 1 SAT" and "sats ##" (## = satellite
         ID number) below.  Soon the Status LED will turn to orange color.
       - The satellite lock progresses with time and more and more satellites
         are locked on.  The display will change to "MODE: AUTO 2-D" and
         eventually to "MODE: AUTO 3-D".
       - Just for double-check: push the "TIME" key once.
         Is the time/date correct (UTC = Japan Time - 9 hours)?
       - Then push the "STATUS" key.
10. The initialization phase is completed once the "AUTO 3-D" mode is
    reached.  [It means, the receiver has locked on to 4 satellites
    simultaneously, which it needs for acquiring a 3-D latitude,
    longitude, and altitude position fix).  This might take a while at
    the radon hut position, somewhere between 10 minutes and 1 hour,
    due to the obstructed view to the sky by the surrounding mountains.
    [When you see the Status LED change to green color (601 model only,
     i.e. the one without large time display) or the '*' symbol on the
     large time display disappear (602 model only) - the configuration
     was successful!]
11. Turn on all cooling fans in the radon hut again that you turned off
    as preparation.
12. Push the START button on the grey control panel to restart the radon
    system.
    - Done. -