Yep. The "civilian channel" on GPS was a gift to everyone from the US
Department of Defense, I suppose they could turn it off if they so wish,
but it is so ingrained in today's culture that they won't. Years ago,
the channel was purposely perturbed to limit the horizontal accuracy to
something between +/-100 to 200 meters. It was called "Selective
Availability."
The US Coast Guard [another branch of the US military] promptly
installed GPS receivers in very carefully surveyed key locations, and
published the error between the known position and the GPS reported
position. They called it Differential GPS. If you had a DGPS receiver,
and were close enough to the DGPS receiver, it would use the broadcast
error to correct the received position. In the US at least, they're
still broadcasting from various sites in the 280 – 460 KHz range which
you can receive if your K3 has the new synthesizer [and you have the
BPSK decoder and a cheat-sheet for the format]. Over time, commercial
interests also began doing this too.
Quite awhile back, someone in the guvmint must have realized that SA
wasn't really working all that well at limiting position precision on
the civilian channel and gave up. The DGPS transmissions continue, or
at least did in 2015. So much these days depends on GPS, it's hard to
see the "100 ms channel" going away.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 1/24/2018 11:18 AM, Ken Chandler wrote:
Course, Governments/Military have overall control over civilian use of the
Birds! or certainly use to have, whether that’s still the case I’m unsure!
Ken.. G0ORH
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