ESTIMATING DELAY CHANGE WHEN MOVING TO A NEW PAD:

For each pad, 'fiberlengths.xls' gives the underground fiber
length U, in nanoseconds, from the IF patch panel in the lab
to the fiber shoebox.  When moving an antenna from pad i to 
pad j,

  delay(j) = delay(i) + U(j) - U(i)

Edit s.delay in subarrayInit.py, then run initialize()
from the sci1 subarray controller to load the new delay
into the correlator.

MEASURING FIBER DELAY WITH THE OTDR:

If the underground delay U to either pad has not yet been
measured, use the OTDR (optical time domain reflectometer)
to measure it.  IMPORTANT: the IF fiber must be disconnected
at the shoebox before making this measurement!

Connect the OTDR to the patch panel with a fiber jumper. 
Use the OTDR in automatic mode (parameters are 1550 nm,
4.1 kilofeet max range, 30 nsec pulse width, 30 sec
averaging time, index of refraction IOR = 1.46833). 
The OTDR reports the fiber length L in feet or kf = kilofeet!
length L in feet (or kf = kilofeet!).

The undeground delay is then given by U = IOR * (L - Lpatch)/c,
where Lpatch is the physical length of the patch cable.  With
L in feet and U in nanosec:

 U = (1.46833 * 12 * 2.54 * 1.e9 / 2.998e10) * (L - Lpatch)

The OTDR also reports the total attenuation through the fiber.
Typically it is < 0.2 dB.  If there is a discontinuity and
reflection loss at ~ 30 feet, this indicates a bad connection
in the antenna patch panels (left 2 racks).