[Elecraft] OT: 3Y0Z Bouvet Island DXpedition

[Dale Chayes]

At the risk of taking us further off topic…..

SA was turned off in May of 2000 by executive order.
https://www.gps.gov/systems/gps/modernization/sa/ <https://www.gps.gov/systems/gps/modernization/sa/>

The position quality transition brought on by the shutdown of SA was a milestone event for the marine research community (among many others.) This event was captured at the time by many and is characterized by the amazing graph on the page above - fond memories.  Some (many of our tiny community) stayed up and watched the data show the transition in real-time - after stumbling around the world’s oceans for a decade it was AWESOME. 

I’ve been working with GPS/GNSS receivers (mostly on research ships at sea, but some geodesy) since the early 1980s when our “portable” (two full height relay racks) Y-set had two HP 2100s and a 9-track tape drive see: https://www.ion.org/museum/item_view.cfm?cid=7&scid=9&iid=43 <https://www.ion.org/museum/item_view.cfm?cid=7&scid=9&iid=43> (the picture only has the receiver hardware, it took serious comping in that era to derive real-time solutions and log the data. Now our cellphones and watches do it.)   Moving that system from ship to ship set the bar for my Compaq “luggable” later on ;-)

A substantial part of the early orbit-correction data collection and analysis that led to differential GPS was led by the civilian surveying and geodesy community trying to figure out how to get high accuracy post-processed solutions during SA.  (Not unlike the amateur radio digital experiments that led to packet radio…

I still do no not take GPS (and GNSS) for granted.

-Dale KB1ZKD
---
"Getting out there and doing it; that’s what really counts. At the end of a career, at the end of anything, it’s not about the awards. It’s about the friends and family.” -Daryl Miller,  McKinley climbing ranger

> On Jan 24, 2018, at 17:41 , Fred Jensen <k6dgw at foothill.net> wrote:
> 
> 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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