I'm not sure whether this has ever been addressed on the CD board. This weekend the admiral and I anchored out in the Piankatank River off the lower Chesapeake Bay. We have anchored there overnight in the past, most recently in July. The last two times we have done so, our Garmin 76 WAAS GPS lost satellite reception for periods of 30 seconds or so. In July another couple reported the same experience. I don't know what model GPS they were using, but it was in exactly the same place in the anchorage. We had perhaps 5-6 satellites locked in when it happened. Fresh batteries, nothing between the GPS and the sky.
Has this happened to others? I'm curious.
Mario
capedory252NOSPAM@aol.com
GPS Deadspots
Moderator: Jim Walsh
-
Ken Coit
Re: GPS Deadspots
Mario,
As reported elsewhere on this board, I have been experiencing strange GPS readings with my Magellan GPS 3000 XL both in stationary and highway condiditons, as well as a stationary Garmin III+. I am currently planning to buy a unit with WAAS for further experimentation and possible installation aboard Parfait. The abrupt location changes are at least sometimes associated with a change in satellite status, but I have not taken the trouble to log all the messages from the GPS for detailed analysis of that after the fact.
I don't think the phenomenon is related to your specific location, but it could be that there is some form of electromagnetic interference that makes some locations less GPS friendly than others. On our most recent road trip there were long segments when the Magellan GPS behaved as one would reasonably expect and other segments where there was a distinct and consistent error for several miles. The errors were clearly bounded. I have the log of the latter half of the trip and will be willing to share it.
I wonder if there is a GPS forum where this is also being discussed, but I haven't found it yet. I have inquiries into the Magellan GPS support people, but I've had no response yet.
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
parfaitNOSPAM@nc.rr.com
As reported elsewhere on this board, I have been experiencing strange GPS readings with my Magellan GPS 3000 XL both in stationary and highway condiditons, as well as a stationary Garmin III+. I am currently planning to buy a unit with WAAS for further experimentation and possible installation aboard Parfait. The abrupt location changes are at least sometimes associated with a change in satellite status, but I have not taken the trouble to log all the messages from the GPS for detailed analysis of that after the fact.
I don't think the phenomenon is related to your specific location, but it could be that there is some form of electromagnetic interference that makes some locations less GPS friendly than others. On our most recent road trip there were long segments when the Magellan GPS behaved as one would reasonably expect and other segments where there was a distinct and consistent error for several miles. The errors were clearly bounded. I have the log of the latter half of the trip and will be willing to share it.
I wonder if there is a GPS forum where this is also being discussed, but I haven't found it yet. I have inquiries into the Magellan GPS support people, but I've had no response yet.
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Mario wrote: I'm not sure whether this has ever been addressed on the CD board. This weekend the admiral and I anchored out in the Piankatank River off the lower Chesapeake Bay. We have anchored there overnight in the past, most recently in July. The last two times we have done so, our Garmin 76 WAAS GPS lost satellite reception for periods of 30 seconds or so. In July another couple reported the same experience. I don't know what model GPS they were using, but it was in exactly the same place in the anchorage. We had perhaps 5-6 satellites locked in when it happened. Fresh batteries, nothing between the GPS and the sky.
Has this happened to others? I'm curious.
Mario
parfaitNOSPAM@nc.rr.com
-
Larry DeMers
Re: GPS Deadspots
That sounds an awful lot like local RF interference is upsetting the Signal to Noise Ratio of the receiver. You can have every single satellite in the lower order (less than bird # 100 I believe) constellations working fine, but if the high order bird (bird # 120 and above) is not being seen by the antenna (like the BBQ was left up and in the way..Dohhh)then you will only get a std. fix..not a Satellite Differential Fix.
Cheers,
Larry DeMers
s/v DeLamer
Cape Dory 30
demers@sgi.com
Cheers,
Larry DeMers
s/v DeLamer
Cape Dory 30
Mario wrote: I'm not sure whether this has ever been addressed on the CD board. This weekend the admiral and I anchored out in the Piankatank River off the lower Chesapeake Bay. We have anchored there overnight in the past, most recently in July. The last two times we have done so, our Garmin 76 WAAS GPS lost satellite reception for periods of 30 seconds or so. In July another couple reported the same experience. I don't know what model GPS they were using, but it was in exactly the same place in the anchorage. We had perhaps 5-6 satellites locked in when it happened. Fresh batteries, nothing between the GPS and the sky.
Has this happened to others? I'm curious.
Mario
demers@sgi.com
-
Mike Nesja
GPS Deadspots, also in Penobscot Bay, Garmin GPS II Plus
Mario,
This is the 3rd year we have been sailing out of Rockland, ME, using our trusty, normally uninteruptable Garmin GPS II Plus (handheld, not DGPS).
During the last few times out (mid-August to Mid-Sept), sailing in the same section of Penobscot Bay we usually frequent, we have experienced dead spots of sufficient duration for the GPS to do a time out and shut down.
I don't have the manual in front of me, but I think the threshold for our GPS unit to shut down is either 3 or 5 minutes. We have replaced the batteries with very fresh ones, and we have added no new equipment or metal objects to the boat. We have not lingered in close proximity to other boats. There is some traffic (including aircraft in/out of Owl's Head) out there, so I suppose we might be getting shut down by RFI coming from some external source.
Next time out (this coming weekend, perhaps), we will try to be a little more observant and see if we can make note of our surroundings (neighbors) at or around the time that the GPS takes a break.
Mike & Erica Nesja
"Wielewaal"
Cape Dory 25D (#045)
nesjaNOSPAM@aol.com
This is the 3rd year we have been sailing out of Rockland, ME, using our trusty, normally uninteruptable Garmin GPS II Plus (handheld, not DGPS).
During the last few times out (mid-August to Mid-Sept), sailing in the same section of Penobscot Bay we usually frequent, we have experienced dead spots of sufficient duration for the GPS to do a time out and shut down.
I don't have the manual in front of me, but I think the threshold for our GPS unit to shut down is either 3 or 5 minutes. We have replaced the batteries with very fresh ones, and we have added no new equipment or metal objects to the boat. We have not lingered in close proximity to other boats. There is some traffic (including aircraft in/out of Owl's Head) out there, so I suppose we might be getting shut down by RFI coming from some external source.
Next time out (this coming weekend, perhaps), we will try to be a little more observant and see if we can make note of our surroundings (neighbors) at or around the time that the GPS takes a break.
Mike & Erica Nesja
"Wielewaal"
Cape Dory 25D (#045)
nesjaNOSPAM@aol.com
-
Ken Coit
Re: GPS Deadspots, also in Penobscot Bay, Garmin GPS II Plus
I have been doing a little reading today and I am more dangerous than ever. Broadcast TV and VHF stations can cause interference with the GPS reception; satellites may be received via multiple paths which will at least confuse the receiver; and at least some receivers use a different algorithm for calculating position when there are fewer than 4 satellites being received. You don't suppose those algorithms get different results do you?
I have also seen the system shut down for several minutes right here in Raleigh, NC; no need to go to Maine to see that phenomenon. It made me wonder if we were under attack at the time.
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
parfaitNOSPAM@nc.rr.com
I have also seen the system shut down for several minutes right here in Raleigh, NC; no need to go to Maine to see that phenomenon. It made me wonder if we were under attack at the time.
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Mike Nesja wrote: Mario,
This is the 3rd year we have been sailing out of Rockland, ME, using our trusty, normally uninteruptable Garmin GPS II Plus (handheld, not DGPS).
During the last few times out (mid-August to Mid-Sept), sailing in the same section of Penobscot Bay we usually frequent, we have experienced dead spots of sufficient duration for the GPS to do a time out and shut down.
I don't have the manual in front of me, but I think the threshold for our GPS unit to shut down is either 3 or 5 minutes. We have replaced the batteries with very fresh ones, and we have added no new equipment or metal objects to the boat. We have not lingered in close proximity to other boats. There is some traffic (including aircraft in/out of Owl's Head) out there, so I suppose we might be getting shut down by RFI coming from some external source.
Next time out (this coming weekend, perhaps), we will try to be a little more observant and see if we can make note of our surroundings (neighbors) at or around the time that the GPS takes a break.
Mike & Erica Nesja
"Wielewaal"
Cape Dory 25D (#045)
parfaitNOSPAM@nc.rr.com
-
Al Smith
Re: GPS Deadspots
Interesting, but I was anchored in Fishing Bay on Thursday night and lost all gps readings for at least 6 hours, from 1800 hours on. It was fine in the morning, with all systems functioning normally. This is known to occur there and to normallize as one leaves the area. Local marinas even have notices posted telling mariners that their gps is not broken.
Al
saylr@adelphia.net
Al
saylr@adelphia.net
-
Ken Coit
Re: GPS Deadspots
Al,
And Fishing Bay is on the Eastern Shore of MD? Could "they" be jamming the system to make sure it works?
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
parfaitNOSPAM@nc.rr.com
And Fishing Bay is on the Eastern Shore of MD? Could "they" be jamming the system to make sure it works?
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Al Smith wrote: Interesting, but I was anchored in Fishing Bay on Thursday night and lost all gps readings for at least 6 hours, from 1800 hours on. It was fine in the morning, with all systems functioning normally. This is known to occur there and to normallize as one leaves the area. Local marinas even have notices posted telling mariners that their gps is not broken.
Al
parfaitNOSPAM@nc.rr.com
-
Larry DeMers
Re: GPS Deadspots
Ken and all,
When conducting these experiments, and when a loss of a solution is found to have happened, look at your signal strength page and note well how many satellites you have showing on the rcvr. and how strong they are. This is the information that will tell you if the satellites are being shut off (no signal strength) or if they are being interfered with (accidently thru RFI from TV and other radio transmitters, or on purpose by jamming). You will see all of the satellites but their signal strength will be poor.
This would help immensely in determining the cause of these problems.
I can say that it does not appear to be a systemic problem (ie: based on the satellites), as I have not seen these dropouts over the weekends on Superior. However, I only sampled two out of seven days, so that is not a good sample. I do know that a jammer will effect the area of the jammer usually, unless the power output of the jammer is high enough and wide enough to include all satellites seen horizon to horizon. That represents a heck of a lot of power and likely several antennas, each aimed at a single satellite. That would be a larger effort and likely noticed too. But it is possible.
My gut feeling is that it is RFi interfering with the rcvr locally. That seems the most likely anyway.
Good work Ken..;^)
Larry DeMers
demers@sgi.com
When conducting these experiments, and when a loss of a solution is found to have happened, look at your signal strength page and note well how many satellites you have showing on the rcvr. and how strong they are. This is the information that will tell you if the satellites are being shut off (no signal strength) or if they are being interfered with (accidently thru RFI from TV and other radio transmitters, or on purpose by jamming). You will see all of the satellites but their signal strength will be poor.
This would help immensely in determining the cause of these problems.
I can say that it does not appear to be a systemic problem (ie: based on the satellites), as I have not seen these dropouts over the weekends on Superior. However, I only sampled two out of seven days, so that is not a good sample. I do know that a jammer will effect the area of the jammer usually, unless the power output of the jammer is high enough and wide enough to include all satellites seen horizon to horizon. That represents a heck of a lot of power and likely several antennas, each aimed at a single satellite. That would be a larger effort and likely noticed too. But it is possible.
My gut feeling is that it is RFi interfering with the rcvr locally. That seems the most likely anyway.
Good work Ken..;^)
Larry DeMers
Ken Coit wrote: Mario,
As reported elsewhere on this board, I have been experiencing strange GPS readings with my Magellan GPS 3000 XL both in stationary and highway condiditons, as well as a stationary Garmin III+. I am currently planning to buy a unit with WAAS for further experimentation and possible installation aboard Parfait. The abrupt location changes are at least sometimes associated with a change in satellite status, but I have not taken the trouble to log all the messages from the GPS for detailed analysis of that after the fact.
I don't think the phenomenon is related to your specific location, but it could be that there is some form of electromagnetic interference that makes some locations less GPS friendly than others. On our most recent road trip there were long segments when the Magellan GPS behaved as one would reasonably expect and other segments where there was a distinct and consistent error for several miles. The errors were clearly bounded. I have the log of the latter half of the trip and will be willing to share it.
I wonder if there is a GPS forum where this is also being discussed, but I haven't found it yet. I have inquiries into the Magellan GPS support people, but I've had no response yet.
Keep on sailing,
Ken Coit, ND7N
CD/14 #538
CD/36 #84 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Mario wrote: I'm not sure whether this has ever been addressed on the CD board. This weekend the admiral and I anchored out in the Piankatank River off the lower Chesapeake Bay. We have anchored there overnight in the past, most recently in July. The last two times we have done so, our Garmin 76 WAAS GPS lost satellite reception for periods of 30 seconds or so. In July another couple reported the same experience. I don't know what model GPS they were using, but it was in exactly the same place in the anchorage. We had perhaps 5-6 satellites locked in when it happened. Fresh batteries, nothing between the GPS and the sky.
Has this happened to others? I'm curious.
Mario
demers@sgi.com
-
Al Smith
Re: GPS Deadspots
The Fishing Bay I was speaking about is at the mouth of the Piankatank River and the Bay on the Middle peninsula on the western Virginia shore. Very strange occurrence there:>).
By the way, it is one of the most beautiful anchorages on the Bay. Try it if you get the chance.
By the way, it is one of the most beautiful anchorages on the Bay. Try it if you get the chance.
-
Ken Coit
Re: GPS Deadspots
I was going to guess that it had something to do with proximity to the Patuxent River Naval Air Station, but I don'thave to guess anymore. Fishing Bay seems to be about 50 miles south of the NAS by my rough calculation.
There are regularly planned outages of GPS service to aviators within 100 NM of the Patuxent River NAS. The vortex is narrower (90 NM radius)at 4000 ft. and presumably at sea level, but who can say? See the link below.
If you are relying on GPS on the Chesapeake Bay anywhere near the Patuxent NAS or the rivers surrounding it, you and your vessel could well be in jeopardy during these times.
I guess that would also keep things confused in DC too, especially to incoming traffic.
Keep on navigating,
Ken
parfaitNOSPAM@nc.rr.com
There are regularly planned outages of GPS service to aviators within 100 NM of the Patuxent River NAS. The vortex is narrower (90 NM radius)at 4000 ft. and presumably at sea level, but who can say? See the link below.
If you are relying on GPS on the Chesapeake Bay anywhere near the Patuxent NAS or the rivers surrounding it, you and your vessel could well be in jeopardy during these times.
I guess that would also keep things confused in DC too, especially to incoming traffic.
Keep on navigating,
Ken
Al Smith wrote: The Fishing Bay I was speaking about is at the mouth of the Piankatank River and the Bay on the Middle peninsula on the western Virginia shore. Very strange occurrence there:>).
By the way, it is one of the most beautiful anchorages on the Bay. Try it if you get the chance.
parfaitNOSPAM@nc.rr.com