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Old 07-02-2020, 11:09 PM   #1
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Coast Guard discontinues differential GPS

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https://www.workboat.com/news/govern...U0ZGc0cFFxQSJ9
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Old 07-03-2020, 06:55 AM   #2
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I guess the question is how many older GPS receivers have been relying on DGPS, and don't support the newer WAAS that replaces it. If I understand this, they will have diminished accuracy once DGPS is turned off. WAAS came out in 2003, so my guess is any GPS receiver introduced since around 2005 probably had WAAS support.
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Old 07-03-2020, 07:02 AM   #3
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Who needs GPS when you have paper charts? Wait, what? no more paper charts either?

I wonder if my Loran "C" still works?

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Old 07-03-2020, 07:48 AM   #4
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For most boat navigation purposes, plain GPS without WAAS, DGPS or anything else is accurate enough. Certainly far closer than the Loran C many managed with for years.
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Old 07-03-2020, 07:51 AM   #5
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Greetings,
Mr. rs. Loran C or older school...


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Old 07-03-2020, 09:00 AM   #6
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Old 07-03-2020, 09:09 AM   #7
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Loran C had great returnable accuracy....till WASS or DGPS came out, the commercial fisherman used LoranC to avoid wrecks and snags....

GPS had similar maybe better absolute accuracy so for navigating it quickly superceded LoranC for navigating ok n.
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Old 07-03-2020, 09:28 AM   #8
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Yes, Loran C was repeatable to within a couple hundred feet. Absolute accuracy wasn't nearly that good though. Unassisted GPS is good to somewhere around 50 feet for both IIRC. Modern receivers that can also use glonass, waas, etc. can do a lot better. With good signal, an average modern cell phone is good to within 10-20 feet.
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Old 07-03-2020, 10:38 AM   #9
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Maybe a couple hundred feet in testing, theory, whatever...but most fishermen I knew swore it was way closer in areas of good crossing lines.

Good enough to trawl/ dredge right past snags.

Doesnt matter, it's like discussing the accuracy of a sextant.
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Old 07-03-2020, 01:10 PM   #10
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Quote:
Originally Posted by twistedtree View Post
I guess the question is how many older GPS receivers have been relying on DGPS, and don't support the newer WAAS that replaces it. If I understand this, they will have diminished accuracy once DGPS is turned off. WAAS came out in 2003, so my guess is any GPS receiver introduced since around 2005 probably had WAAS support.
How about older units that didn't even have the Differential station capability? My Garmin GPS 128 is that old. Without the DGPS I have never had any hesitation in relying on its accuracy. I should see no difference whatsoever now that there is no DGPS. My Dinghy and FB is a Humminbird 757C, also an older unit, but has WAAS technology, so again should see no difference.
I suspect DGPS dropping to GPS will be undetectable, except for those users who need the best possible reception, but those folks have long ago moved up to more modern technology.
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Old 07-03-2020, 03:02 PM   #11
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I believe the DGPS by the USCG was to overcome the selective availability degradation when it was activated as commercial shipping was becoming more dependent on GPS accuracy. It also improved overall accuracy but not to a great degree and had limited range.

DGPS has been disestablished in many locations for awhile now. Hardly any recreational units have had it for years and years now....you needed a special unit and antenna to even get it when it was popular.

The FAAs WAAS was being developed around the same timeframe and was more "user friendly" thus driving the direction of making GPS more accurate.
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Old 07-03-2020, 03:31 PM   #12
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DGPS has been disestablished in many locations for awhile now. Hardly any recreational units have had it for years and years now....you needed a special unit and antenna to even get it when it was popular.

We had it. Furuno GP-39, from circa 2002 and that came installed on the boat when we got it...

I didn't really notice any better accuracy compared to the newer GP-330 that we installed in 2009... but then again the other unit was WAAS-corrected and it would have been difficult to do meaningful comparisons anyway.

One thing that surprised me; we often got an error warning when going down the central and then southern part of Delaware Bay. The error message was about connectivity, and at first I wondered why we might have lost satellite reception there... out in the wide open middle of the Bay. And the thing still displayed our coordinates similar to the other unit onboard. In retrospect, I began to suspect we were losing the differential signal instead.

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Old 07-03-2020, 04:42 PM   #13
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I always know exactly where I am it's other things whereabouts I wonder about...
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Old 07-03-2020, 05:37 PM   #14
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Chris....pretty sure the DGPS site for our area was in the Annapolis area. It was only supposed to barely reach the Delaware coast and because it was a land based signal...because it crossed the Delmarva peninsula, it could have affected the DelBay area reception.
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Old 07-04-2020, 06:25 AM   #15
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Chris....pretty sure the DGPS site for our area was in the Annapolis area. It was only supposed to barely reach the Delaware coast and because it was a land based signal...because it crossed the Delmarva peninsula, it could have affected the DelBay area reception.

Yep, that would explain. I though the relevant differential transmitter was in NJ somewhere...

I mispoke; the earlier one was a GP-36. The unit began to loose pixels on the screen, though, so I replaced it with a newer GP-39 WAAS-corrected unit, drop-in replacement, all good... but we haven't been out to the coast since then to sorta-kinda confirm the GP-36 alarm was about the differential signal...

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Old 07-04-2020, 06:47 AM   #16
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Yep, that would explain. I though the relevant differential transmitter was in NJ somewhere...

I mispoke; the earlier one was a GP-36. The unit began to loose pixels on the screen, though, so I replaced it with a newer GP-39 WAAS-corrected unit, drop-in replacement, all good... but we haven't been out to the coast since then to sorta-kinda confirm the GP-36 alarm was about the differential signal...

-Chris
At first I believe there was one either in Cape May or Delaware someplac

But it was discontinued many years ago because the transmitter in Annapolis supposedly served the traffic headed into the Delaware Bay, possibly Norfolk too. It wasn't great, but good enough....plus WAAS GPS was getting better.

The USCG is always fighting a budget crunch one way or another, so systems ir operations that aren't really being used get the ax pretty early if they can.
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Old 07-04-2020, 06:55 AM   #17
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Yep, all that makes sense... thanks for info.

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Old 07-04-2020, 07:09 AM   #18
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I just happened to be in USCG Cape May during most of this....including some of the preliminary meetings with the USCG and the FAA when both were just starting the DGPS/WAAS programs.
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