note....it is not possible at present to calculate phase delay
doppler and time delay observables in the same series. if
this feature is to be added in the future, the npath logic,
idopob logic, utrsav logic, and logic in calling propco all
must be checked and changed. it will be necessary to call
radctl three times: in the middle (for tmdly), and 2 ends
(for phase delay doppler) of the count interval.

the first time through, npath is 1. pos, delay, and vel2 are
saved, utrec is updated, idopob is updated, npath is incremented
and then it exits. the next time it enters phadop, npath is 2.
the pos, vel2, and delay are saved, and then phase delay doppler
is calculated. npath is set to 1 in anticipation of the next
observation.