Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
joebrown@mint..net
Loran vs. GPS, a comparison
Moderator: Jim Walsh
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Richard Feffer
Re: Loran vs. GPS, a comparison
Joe,
As I recall, when using Loran, you need to enter a correction factor. You do this by placing your boat at a location with published Lat/Lon and telling your unit that's where you are. The instructions that came with your Loran should give you specific information on this subject. I think once you enter your correction, you'll find them to have a smaller difference. They will never be exactly the same. GPS is more accurate.
Hope this answers your question.
richfef@prodigy.net
As I recall, when using Loran, you need to enter a correction factor. You do this by placing your boat at a location with published Lat/Lon and telling your unit that's where you are. The instructions that came with your Loran should give you specific information on this subject. I think once you enter your correction, you'll find them to have a smaller difference. They will never be exactly the same. GPS is more accurate.
Hope this answers your question.
Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
richfef@prodigy.net
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Tom
Re: Loran vs. GPS, a comparison
Joe, Plugging in waypoints is not a good test for your LORAN. What they are good at doing is bringing you back to the same place a second time. (We're talking a few feet here, not 50 or 60 yards) If you sail to the place and enter it in your LORAN as a waypoint it should be able to bring you right to it the next time. It's not as good when entering coordinates off a chart. I have both a Magellan GPS and a Morrow LORAN. I prefer the LORAN because the operation of it is much simpler and the repeatability is flawless. I mainly use the GPS when I'm sailing foreign or as a back up to the LORAN in tricky conditions. You know that most LORANs can be adjusted to correct for that 3/10s of a mile if it is consistently off in one direction. (That's the ususal case)Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
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Craig Urquhart
GPS vs. GPS, a comparison
Joe,
I carry a Magellan 5000D and a Garmin 45 on Satu, my CD27 and like you, frequently navigate Maine's fog. My two GPS handhelds generally agree. The Magellan has never burped or unknowingly provided bad position info, so I've come to trust the Magellan implicitly.
The Magellan has icons and annunciation for poor geometry and signal strength. The older Garmin 45 has a distance figure which is an indication of accuracy, presumably based on signal strength and geometry, but has no annunciation tied to it. I've seen the Garmin plug away with a 500 foot indicated error and provide no indication of trouble. I ran into this problem last summer on Penobscot Bay at night, when my radar and GPS disagreed.
My recollection from the sofa is that the Garmin will only annunciate "Poor GPS Coverage", under extreme circumstances, such as being placed under cockpit cushions.
With poor signal or geometry quality, no instrument is reliable. So my number one rule for the GPS is, mount the unit/antenna in a location which provides unobstructed coverage and monitor the signal quality on a regular basis, particularly when navigating in tight places. Also watch the compass to be sure that the boat is, to a reasonable extent, tracking the GPS track data.
The Garmin 45, for reasons still unclear to me, almost put me on the rocks a couple of years back with a huge error(1/2 mile), while traveling in dense fog around Seguin Island. It may have been due to poor geometry, but the Garmin was telling me it was ok. When I flipped it to the plotter display, my boat was zig zagging side to side in steps of approximately 1/2 mile. I cycled power on the unit and obtained the same result. Next, I plugged the L/L waypoint data into the Magellan and it worked perfectly, showing no indication of poor signal strength or geometry.
You can draw your own conclusions here. As for me, I use the Garmin because it "talks" to my laptop and it does a nice job 99% of the time. But if I didn't have radar, I'd still use the Magellan in tight foggy passages.
Craig Urquhart
Satu CD27 #272
Satu@gwi.net
I carry a Magellan 5000D and a Garmin 45 on Satu, my CD27 and like you, frequently navigate Maine's fog. My two GPS handhelds generally agree. The Magellan has never burped or unknowingly provided bad position info, so I've come to trust the Magellan implicitly.
The Magellan has icons and annunciation for poor geometry and signal strength. The older Garmin 45 has a distance figure which is an indication of accuracy, presumably based on signal strength and geometry, but has no annunciation tied to it. I've seen the Garmin plug away with a 500 foot indicated error and provide no indication of trouble. I ran into this problem last summer on Penobscot Bay at night, when my radar and GPS disagreed.
My recollection from the sofa is that the Garmin will only annunciate "Poor GPS Coverage", under extreme circumstances, such as being placed under cockpit cushions.
With poor signal or geometry quality, no instrument is reliable. So my number one rule for the GPS is, mount the unit/antenna in a location which provides unobstructed coverage and monitor the signal quality on a regular basis, particularly when navigating in tight places. Also watch the compass to be sure that the boat is, to a reasonable extent, tracking the GPS track data.
The Garmin 45, for reasons still unclear to me, almost put me on the rocks a couple of years back with a huge error(1/2 mile), while traveling in dense fog around Seguin Island. It may have been due to poor geometry, but the Garmin was telling me it was ok. When I flipped it to the plotter display, my boat was zig zagging side to side in steps of approximately 1/2 mile. I cycled power on the unit and obtained the same result. Next, I plugged the L/L waypoint data into the Magellan and it worked perfectly, showing no indication of poor signal strength or geometry.
You can draw your own conclusions here. As for me, I use the Garmin because it "talks" to my laptop and it does a nice job 99% of the time. But if I didn't have radar, I'd still use the Magellan in tight foggy passages.
Craig Urquhart
Satu CD27 #272
Joe Brown wrote: Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
Satu@gwi.net
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warren
Re: Loran vs. GPS, a comparison
Joe -Joe Brown wrote: Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
Loran waves can be bent by the coastal topography, resulting in an inaccurate position. There are places in Maine where this is particularly a problem, and I am not sure but what the area around Rockport is one of them. Check with the local cruising guides and charts. However, the error is always the same, and the reproducibility of a Loran position is outstanding (within a few feet). If you ever lose something or someone overboard, it is better to mark the position with the Loran.
The absolute accuracy of GPS (without differential) is within 100 yards 95% of the time. This is often better than Loran. The reproducibility of the GPS position is less, due to the random error introduced by Selective Availability. With differential, GPS accuracy is within 5 - 10 yards 95% of the time and reproducibility of the position is the same.
By the way, one hazard of GPS is that many areas of the world are charted incorrectly. Your position may be correct, but you are still on the reef your chart says is a quarter mile away. This problem comes about because GPS is not referenced to land the way Loran and visual piloting are. In all honesty, this is probably not much of a problem along the US coast, but is known to be a problem in the Carribbean.
Hope this helps.
Warren
wstringer@aristotle.net
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Lee H. Hodsdon
Re: Loran vs. GPS, a comparison
Joe,
A subject near and dear to my heart. Our 25D came with the original (1984) Morrow unit, which performed perfectly for the first two years. We used the unit to navigate from Portsmouth, NH to Searsport, ME. Because Loran is high in "repeatable accuracy" we entered our waypoints as we passed a specific navigational aid, regardless of error in "ultimate accuracy". The idea being that we could always return to this exact spot when necessary. If we were in a new area, I would compare the loran position to the chart position, and alter the Lat and Long offset till the positions agreed. These offset values were recorded on the chart for future reference. Once the values agreed, we could navigate to a position safely. This was kind of a pain, but it worked. As Frank Luke says, "The bouys may move, but the rocks stay put". On one trip from Trafton Island to Bunker Cove, Roque Island in dense fog, we found the kind of signal loss that one of the posters mentioned. I think the quote from my wife was, "What does it mean when the numbers keep changing?" We were just entering the Moosabec Reach. The trip through the passage was interesting, watch and compass but we made it OK. We replaced the Morrow with an inexpensive unit, it worked for one year then quit -- kind of false economy I guess.
My next replacement was a Raytheon GPS setup, 298 display, and 112 antenna. All this is linked to a Raytheon 2000+ Autopilot. This unit won't loose its' signal, unless the entire system goes down. The repeatable accuracy is much poorer than the Loran, but the ultimate accuracy may be better depending on the signal degradation provided by Uncle Sam. I guess a DGPS unit will correct this, though at a high cost. I would very much like to find a Loran antenna for the 298, but this has been impossible.
So now that I've rambled for a while -- I'd keep the Loran, enter the waypoints as you pass them, it will always take you back to the same spot and the system is going to be around for a while (2008 if my memory is correct, I'm certain someone will know). Use this in conjunction with your GPS unit for areas of poor Loran signal strength. Maybe the GPS signal degradation will be a thing of the past. Go where the rocks aren't and have a ball! Oh, and keep a runing DR position, so when the electronics fail you know where you are, and where you have to go.
Sincerely,
Lee
lhodsdon@nh.ultranet.com
A subject near and dear to my heart. Our 25D came with the original (1984) Morrow unit, which performed perfectly for the first two years. We used the unit to navigate from Portsmouth, NH to Searsport, ME. Because Loran is high in "repeatable accuracy" we entered our waypoints as we passed a specific navigational aid, regardless of error in "ultimate accuracy". The idea being that we could always return to this exact spot when necessary. If we were in a new area, I would compare the loran position to the chart position, and alter the Lat and Long offset till the positions agreed. These offset values were recorded on the chart for future reference. Once the values agreed, we could navigate to a position safely. This was kind of a pain, but it worked. As Frank Luke says, "The bouys may move, but the rocks stay put". On one trip from Trafton Island to Bunker Cove, Roque Island in dense fog, we found the kind of signal loss that one of the posters mentioned. I think the quote from my wife was, "What does it mean when the numbers keep changing?" We were just entering the Moosabec Reach. The trip through the passage was interesting, watch and compass but we made it OK. We replaced the Morrow with an inexpensive unit, it worked for one year then quit -- kind of false economy I guess.
My next replacement was a Raytheon GPS setup, 298 display, and 112 antenna. All this is linked to a Raytheon 2000+ Autopilot. This unit won't loose its' signal, unless the entire system goes down. The repeatable accuracy is much poorer than the Loran, but the ultimate accuracy may be better depending on the signal degradation provided by Uncle Sam. I guess a DGPS unit will correct this, though at a high cost. I would very much like to find a Loran antenna for the 298, but this has been impossible.
So now that I've rambled for a while -- I'd keep the Loran, enter the waypoints as you pass them, it will always take you back to the same spot and the system is going to be around for a while (2008 if my memory is correct, I'm certain someone will know). Use this in conjunction with your GPS unit for areas of poor Loran signal strength. Maybe the GPS signal degradation will be a thing of the past. Go where the rocks aren't and have a ball! Oh, and keep a runing DR position, so when the electronics fail you know where you are, and where you have to go.
Sincerely,
Lee
Joe Brown wrote: Aboard my Cape Dory 28, purchased last Fall, I use a hand-held Garmin 45 GPS as my primary navigation tool, and the boat was also equipped with Loran. Out of curiosity, I plugged several waypoints into each instrument today, using the exact same L/L coordinates for each, for comparison. While the bearing was within 1 degree on the two instruments, the distance from my boat to each WP varied from 3/10ths to a half mile. That's not a lot on the face of the globe but a tremendous amount when navigating, say, in a fog as we habitually have in Maine. In a former boat, my GPS could bring me to within 50 or 60 yards of a WP target, and I trust it implicitly. Anyone else with such comparative experience with Loran and GPS? - Joe Brown, CD-28 "Caprice," Rockport, Maine.
lhodsdon@nh.ultranet.com
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D. Stump, Hanalei
Re: Accuracy versus Precision
Joe,
Just something else to think about...Accurate means you HIT the target, Precise means you hit the bullseye! You need to be accurate when launching nuclear tipped missiles, but precise if using a .223 calibre rifle! Same holds true for picking up that MOB, Precise is exactly what you want, accurate means a drowned crewmate and numerous lawsuits! If MOB, mark the spot with the Loran! If I want Hanalei to "Precisely" get into New Harbour on Block Island, I'll use the Loran every time. To check my accuracy on course, I'll have the GPS sitting on the seat next to me while I"m at the helm. And yes, to be Precise, the Loran should be sailed to the spot and marked electronically! And finally, always remember: Log, Lead, and Lookout! ie: Keep a Deadrecon. log, watch the depth meter, and post a competent lookout.
The selective availability of GPS is a joke the government has played on us. Think about it, if you wanted to locate the precise coordinates of an important target(read that as "place to go to") in the U.S., you buy a standard GPS, and that will get you close or "accurate". If you want precision, add differential GPS (based on land based radio stations provided by: yep, you guessed it, our government) and your targeting information is now almost as precise as non-selective availability GPS! Don't you just love it when our tax dollars do so much good! I love it when a plan comes together!
Isn't this fun??? I would keep both devices, and use them with knowledge of what they are telling you and an awareness of each units limitations.
Dave Stump
Captain Commanding
s/v Hanalei (CD-30)
Just something else to think about...Accurate means you HIT the target, Precise means you hit the bullseye! You need to be accurate when launching nuclear tipped missiles, but precise if using a .223 calibre rifle! Same holds true for picking up that MOB, Precise is exactly what you want, accurate means a drowned crewmate and numerous lawsuits! If MOB, mark the spot with the Loran! If I want Hanalei to "Precisely" get into New Harbour on Block Island, I'll use the Loran every time. To check my accuracy on course, I'll have the GPS sitting on the seat next to me while I"m at the helm. And yes, to be Precise, the Loran should be sailed to the spot and marked electronically! And finally, always remember: Log, Lead, and Lookout! ie: Keep a Deadrecon. log, watch the depth meter, and post a competent lookout.
The selective availability of GPS is a joke the government has played on us. Think about it, if you wanted to locate the precise coordinates of an important target(read that as "place to go to") in the U.S., you buy a standard GPS, and that will get you close or "accurate". If you want precision, add differential GPS (based on land based radio stations provided by: yep, you guessed it, our government) and your targeting information is now almost as precise as non-selective availability GPS! Don't you just love it when our tax dollars do so much good! I love it when a plan comes together!
Isn't this fun??? I would keep both devices, and use them with knowledge of what they are telling you and an awareness of each units limitations.
Dave Stump
Captain Commanding
s/v Hanalei (CD-30)
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Darin Bartram
Re: Accuracy versus Precision
Well, with the risk that Walt will delete this for being unrelated to Cape Dory, or otherwise just a boring waste of space on the BB, I'd like to add my two cents to the accuracy vs. precision comment, lest people interpret Dave's comments to indicate that precision is closer to "true" than accuracy is.
Accuracy and precision have separate purposes in science but seem to be used interchangeably just about everywhere else. Accuracy refers to how closely data approach the "true" value (or, at least, how closely the data approach agreed upon values, based on measurements using the best techniques available). In this case, accuracy would be the device's ability to compute the exact longitude and latitude coordinates. Thus, the ability of the GPS to compute the known coordinates of a location is a measure of its accuracy.
Precision actually has no relation to the "true" value, but instead is an indication of repeatability. If your Loran gives the same reading every time you turn it on while sitting in your slip or when you are at a fixed marker, it is said to be precise, whether or not it computes the "true" coordinates of your location. If you were to calculate the standard deviation of the readings, you would find that a more precise instrument has a lower standard deviation than a less precise instrument.
In general, the Loran is considered to be more precise, and the GPS is considered to be more accurate. If you have been to a bouy before and marked it, the Loran will get you closer to it again than a GPS will. If you have never been to the bouy before, but can program its coordinates, the GPS should do a better job. So, everything else Dave says is correct.
dbartram@hunton.com
Accuracy and precision have separate purposes in science but seem to be used interchangeably just about everywhere else. Accuracy refers to how closely data approach the "true" value (or, at least, how closely the data approach agreed upon values, based on measurements using the best techniques available). In this case, accuracy would be the device's ability to compute the exact longitude and latitude coordinates. Thus, the ability of the GPS to compute the known coordinates of a location is a measure of its accuracy.
Precision actually has no relation to the "true" value, but instead is an indication of repeatability. If your Loran gives the same reading every time you turn it on while sitting in your slip or when you are at a fixed marker, it is said to be precise, whether or not it computes the "true" coordinates of your location. If you were to calculate the standard deviation of the readings, you would find that a more precise instrument has a lower standard deviation than a less precise instrument.
In general, the Loran is considered to be more precise, and the GPS is considered to be more accurate. If you have been to a bouy before and marked it, the Loran will get you closer to it again than a GPS will. If you have never been to the bouy before, but can program its coordinates, the GPS should do a better job. So, everything else Dave says is correct.
D. Stump, Hanalei wrote: Joe,
Just something else to think about...Accurate means you HIT the target, Precise means you hit the bullseye! You need to be accurate when launching nuclear tipped missiles, but precise if using a .223 calibre rifle! Same holds true for picking up that MOB, Precise is exactly what you want, accurate means a drowned crewmate and numerous lawsuits! If MOB, mark the spot with the Loran! If I want Hanalei to "Precisely" get into New Harbour on Block Island, I'll use the Loran every time. To check my accuracy on course, I'll have the GPS sitting on the seat next to me while I"m at the helm. And yes, to be Precise, the Loran should be sailed to the spot and marked electronically! And finally, always remember: Log, Lead, and Lookout! ie: Keep a Deadrecon. log, watch the depth meter, and post a competent lookout.
The selective availability of GPS is a joke the government has played on us. Think about it, if you wanted to locate the precise coordinates of an important target(read that as "place to go to") in the U.S., you buy a standard GPS, and that will get you close or "accurate". If you want precision, add differential GPS (based on land based radio stations provided by: yep, you guessed it, our government) and your targeting information is now almost as precise as non-selective availability GPS! Don't you just love it when our tax dollars do so much good! I love it when a plan comes together!
Isn't this fun??? I would keep both devices, and use them with knowledge of what they are telling you and an awareness of each units limitations.
Dave Stump
Captain Commanding
s/v Hanalei (CD-30)
dbartram@hunton.com
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Olli Wendelin
Navigation
"I trust it implicitly"
As GPS has become more available (cheaper), I have noticed the number of magazines articles on groundings increase. Mostly because people read the numbers on the GPS and assumed that's where they were. There are many reasons why this may not be true; conflicting datums, outdated chart, GPS inaccuracy, satellite angle, poor antenna, proximity to florecent lighting, etc.
To me the biggest problem is blindly following one source of position information. Navigation is the art of using all information to safely guide your ship. I had to review the ships position constantly when Officer of the Deck in the Navy. We had many sources of position information; Dead Reckoning, Visual, Celestial, Loran A, Loran C, Omega, NAVSAT, and Ships Inertial Navigation System (SINS). These were plotted on the chart and compared with soundings and radar. They were always a cluster, never a dot. Seldom was ships position considered a certainty, it was a circle of probability. The better the position information, the smaller the circle.
Someone mentioned taking there ship into a harbor in the fog trusting GPS. I would prefer sharp lookouts, radar, local knowledge, and dead reconning (with GPS as a backup), or maybe I would just wait for the fog to clear.
Olli Wendelin
BLUE MOON
Charleston, SC
wendelin@spawar.navy.mil
As GPS has become more available (cheaper), I have noticed the number of magazines articles on groundings increase. Mostly because people read the numbers on the GPS and assumed that's where they were. There are many reasons why this may not be true; conflicting datums, outdated chart, GPS inaccuracy, satellite angle, poor antenna, proximity to florecent lighting, etc.
To me the biggest problem is blindly following one source of position information. Navigation is the art of using all information to safely guide your ship. I had to review the ships position constantly when Officer of the Deck in the Navy. We had many sources of position information; Dead Reckoning, Visual, Celestial, Loran A, Loran C, Omega, NAVSAT, and Ships Inertial Navigation System (SINS). These were plotted on the chart and compared with soundings and radar. They were always a cluster, never a dot. Seldom was ships position considered a certainty, it was a circle of probability. The better the position information, the smaller the circle.
Someone mentioned taking there ship into a harbor in the fog trusting GPS. I would prefer sharp lookouts, radar, local knowledge, and dead reconning (with GPS as a backup), or maybe I would just wait for the fog to clear.
Olli Wendelin
BLUE MOON
Charleston, SC
wendelin@spawar.navy.mil
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D. Stump, Hanalei
Re: Accuracy versus Precision
Darin,
You are PRECISELY correct. Thanks for your input. I don't think Walt will delete this as it is something that adds to all of our knowledge. It's about things we don't usually think about. Good discussion!!
Dave Stump
Captain Commanding
s/v Hanalei (CD-30)
You are PRECISELY correct. Thanks for your input. I don't think Walt will delete this as it is something that adds to all of our knowledge. It's about things we don't usually think about. Good discussion!!
Dave Stump
Captain Commanding
s/v Hanalei (CD-30)
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Stickler
Re: Accuracy versus Precision
It is possible (and likely) to be precisely WRONG. Accuracy is the goal. Precision is merely a measure of the measure (1%, 5% or 10% or whatever). Believe me you can measure to the .0001 of a degree, but if you have sighted in on the wrong landmark....
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Larry DeMers
Re: Loran vs. GPS, ASF, and more...
Local disturbances using LORAN are more due to the dielectric transistion found when the signal goes from earth under it to water under it. This has been recognized, and in fact many charts have compensated for this already (my Lake Superior set is compensated this way, and is marked "ASF corrected"). This correction is known as ASF, or Additional Secondary Factor. It is correct that you can enter this into your LORAN anytime you feel that it is warranted. ie: You are standing at a landmark of known location, and the loran shows you a 1/8th mile away..you can put that place dead-nuts on, and then the readings int hat general area will be have their accuracy increased by your correction. However, once leaving that area, turn off the correction that you input, as it is no longer valid.
The FAA and the CG are bringing another constellation of satellites on line over the next year or so, which will have the GPS differential time correction signals encoded on the GPS signal, so that your receiver will be compatible (with appropriate soft and firmware upgrades), without an external rcvr. or antenna. That is one reason why you want to buy a GPS with as many satellite channels as possible..like 12 would be great. Not every satellite you are tuned to will have the DGPS encoded signal on it's transmitter, so if you have the ability to get multiple satellites, you would have the opportunity to pick and choose which have the desired signals.
This will then bring us full circle; the Government "gave" us GPS, they took away the accuracy that makes it useful, then they will be "giving" it back to us at additional costs. Ain't it grand!
demers@sgi.com
The FAA and the CG are bringing another constellation of satellites on line over the next year or so, which will have the GPS differential time correction signals encoded on the GPS signal, so that your receiver will be compatible (with appropriate soft and firmware upgrades), without an external rcvr. or antenna. That is one reason why you want to buy a GPS with as many satellite channels as possible..like 12 would be great. Not every satellite you are tuned to will have the DGPS encoded signal on it's transmitter, so if you have the ability to get multiple satellites, you would have the opportunity to pick and choose which have the desired signals.
This will then bring us full circle; the Government "gave" us GPS, they took away the accuracy that makes it useful, then they will be "giving" it back to us at additional costs. Ain't it grand!
demers@sgi.com