DGPS Radiobeacon Receiver?

[kennharriet]

Our "new to us" 22 Cruiser has a West Marine, WM-DBR Automatic DGPS Radiobeacon Receiver in it. I can not find it in the West Marine catalog. What is this device and it's function?

[matt_unique]

[journey on]

DGPS is Differental GPS, where a ground station is used to correct for GPS errors. The ground station knew where it was, received a "normal" GPS signal, calculated the required corrections and broadcast these corrections on a different frequency. Thus you needed two antennas, etc. Most of these ground stations were at large ports, to make sure that really, really big ships didn't get in trouble.

With WAAS, the corrections are still calculated by ground stations, but are now uploaded to satellites, and can be received by WAAS enabled GPS receivers. These corrections work everywhere. and you only need the one antenna. WAAS enabled GPS receivers are the norm and are the reason GPS has become very accurate. Beats a sextant and watch. One can upgrade for ~$250.

Boris

[kennharriet]

Thanks for the information. I think I will remove it. I have a Lorance hard mount GPS and a Garmin handheld back-up. The antenna was not in a good location anyway.

Maybe I can use it for a back-up anchor, unless someone wants to purchase it for it's antique value?

[Dreamer]

Ken,

I wouldn't be in too big of a hurry to upgrade. The DGPS system is very accurate. We used it on a trawler and compared it to newer systems. It was always comparable down to a thousandth of a minute of Latitude or Longitude. (about 6 feet)
Good Luck with the new boat.

[wailedcentipede]

if you type into a search (DGPS radiobeacon) you will come up with lots of information .. at a glance you have maybe a little bit more like big boat gear ... did not dig deep but you may also need a chart to mark your position ... theirs also different type antennas one like those gps type .. i would keep it if nothing else a conversation piece ... wc

[stevej]

My Furuno DGPS uses a combination of loran and GPS to determine position. Works beautifully and is generally able to determine my position within 3 feet or less.

Have not kept up with WAAS transmitting locations but I believe that here on the left coast it was not an active service until recently (there may still be some areas without coverage).

My main concern was the decommissioning of the loran transmitters but I think that has been put on hold for now.

DGPS is as accurate as WAAS and going to be around for a few more years.

stevej

[journey on]

DGPS is as accurate as WAAS because they both use the same ground based corrections. The difference is in how the corrections are distributed. If you're always near a DGPS transmitter you're in good shape. If not, then WAAS covers a wider area.

When we got Journey On, the display came with a WAAS enabled GPS, and I never found it to be more than a few feet off, using C-map charts for display. That's the beauty of the new integrated display. WAAS/GPS gives you your location and the display plots it on a moving chart for you. Reduces navigation to a no brainer, except for the intelligence to see if it's crapped out. I think it's like cheating, look at all the push-ups one had to do without GPS plotters. When was the last time you estimated your position by DR? And your plotter will tell you when you'll get there. I sold my sextant, don't need a watch.

Do not use the above statements as a substitute for navigation. Only rely on official Coast Guard statements. And if you think that's scary, the FAA is flying aircraft with WAAS/GPS. They didn't do it for recreational boaters.

Boris

[kennharriet]

The DGPS unit is separate from the GPS unit. The DGPS box only has a "power" light and a lock "light". It does not have a display. I do not understand how it is tied to the GPS unit and the resulting increased accuracy.

[thataway]

In order to use a differential GPS receiver, you have to have a GPS which is set up to use this unit. Since WAAS is available on virtually all new GPS units, there are few current GPS units which use the separate receiver.

The Diff. GPS is transmitted on the old lighthouse radio direction finder frequencies--often the same fequencies as were used in that service. This is 283.5 to 325 Khz. or long wave. The correction is made for that specific location, and the closer you are to the location, the better the accuracy. In Pensacola we can receive 3 DGPS frequencies, and they are all close. Mobile Alabama is about 50 miles away. The nearest WAAS ground stations are Houston,TX, Jacksonville FL and Atlanta, GA. Theoretically the DGPS could be slightly more accurate, since we are closer to a base station--and this was definately true when we only had a few ground stations. The WAAS system was founded for aviation. Although there are some places where it is over 200 NM between WAAS stations, it is still accurate for boating use. What happened 2 years ago was that the satellites for WAAS were switched--and an area in Canada and the NE was better served with the new satellite--nothing to do with ground station and accuracy from existing stations. Since the WAAS is from Satellite signals, it is available where these specific satellites are in view: The West Coast now has 4 satellites possible in view--the East Coast only 2--far East only one.

There is no connection between differential GPS and Loran (either C or e)--Loran operates on very long wave (100Khz)--and is due to be phased out next year. I suspect that this will happen this time around. Also, remember that although the repeatiblity of Loran is excellent, its absolute position accuracy is not as good, due to different radio wave propogation over land and water masses.

[kennharriet]

So, the DGPS would have to be hard wired to the GPS to be providing greater accuracy. If it is not, I may as well remove it right?

I am impressed with your knowledge of the subject. How did you come by that?

[Doryman]

[thataway]

Yes, you have to connect the unit to a suitable GPS.

Thanks for the kind words, but my knowledge is in narrow fields. Basically I live through an era of changing navigation for pleasure boats. I started navigating as a child with only a compass, chart, eyes and ears. I grew up as these technologies evolved. First was using the radio direction finder, where the radio signal was timed with the fog horn. Since radio waves travel at the speed of light and the diaphone (fog horn) at the speed of sound, it was easy to calculate the distance from the light house by counting the seconds. The next steps in navigation for me, were the sextant, tables and manual calculations. Hand held computers made the calculations easier, and about that time a few of us put VOR Omni airplane receivers on our boats for better directional calculation and triangulation. Next came Loran (A and then C)--and Omega (a long wave system used mostly by the navy: especially aircraft and submarines) Finally a really accurate system came long: Sat Nav (precursor of modern GPS, in that you only got the accurate position when the Satellite was in view--and that was on an average of every 6 hours.) Between fixes, the navigation was by "Dead dead reckoning". Either the navigator entered speed and heading every 30 minutes or so--or there was a "computer" which read the speed and direction (compass). Actually this was fairly accurate. We paid $3500 for one of the first units, and only got it because we knew a vice president of Magnavox Finally in 1990 the first civilian GPS units were available to the public. We took the first unit to Australia in Dec. 1990. I had ordered it 6 weeks before we left and it was the "mark 1 version" we obtained the mark 6 version and "burned it in" in our car on the way to the airport. GPS were generally in very short supply because of the Gulf war and SA (selective averaging--which intentionally introduced an error) was turned off. SA was finally completely removed for civil use in 2000.

We were very fortunate, living in S. Calif. where there was an abundance of military and aviation surplus equipment available at cheap prices, to use on our boats. Plus many sailors worked in the aviation and electronics industry and often were good sources for navigation gear.