--- "Clint Wolff (VAX collector)" <vaxman_at_qwest.net> wrote:
>
> There used to be a lot of WWV receivers available to pick up time
> from the NBS broadcasts, but they seem to have gone away with the
> arrival of GPS.
Good point. Rand-McNalley sells a laptop GPS for about $80 with no
software - PS/2 mouse port for power and DE-9 for data. I have one
that I use in the car and the airplane (I have a 9-pin null-modem
dongle so I can use the GPS with my Palm Pilot and GPS Pilot software).
I really should have remembered this - the first time I encountered using
GPS strictly as a time-base was on a NASA project to track the IMP-8 satellite
(launched over 30 years ago, so on-topic!). It's a solar wind satellite that
orbits about 100,000 miles up, outside the Van Allen belts. A consequence of
it being old is that it has no store-and-forward capability. It broadcasts
in real time (somewhere in the 2m band) so if you want the data, you'd better
be under it to catch it. I monitored the only IMP-8 ground station in the
Southern Hemisphere, at McMurdo Station, during the winter of 1995. The GPS
comes in because they needed to know *exactly* what time it was so the antenna
could track the satellite as it moved across the sky. It has a complex orbit;
there are no 2-line elements for it - we ftp'ed a file every week with the
anticipated azimuth/elevation numbers for a given time and the antenna
controller tracked it as it flew overhead. The antenna and positioners were
not a robust system (it broke several times due to the wind and cold), but the
PeeCee *did* always know what time it was.
-ethan
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Received on Thu Jul 26 2001 - 09:53:03 BST