Flashback Max
Homer, NY
New Member
Joined: 07/19/2004
View Profile
 Offline
|
I was talking to a friend of mine about GPS and sat. radio. He brought up the idea that they might not work in Alaska; the satellites would not cover there or whatever. I don’t know, so I wondered if people had any experience? Thanks
|
joe b.
Florida
Senior Member
Joined: 08/24/2002
View Profile
 Online
|
GPS does work in the far north due to the circumpolar routes of some of the satellites circling the earth. (in theory anyway)
However with that said, I have found that some of the GPS units I have used in the past have problems "interpreting" the info they receive from the satellites due to the convergence of the satellite routes as they cross over the poles. I had one that consistently showed me to be about 100 meters north of my actual position which made the GPS unit "think" I was off route and it didn't like it and tried to keep rerouting me.
One of the main satellites used for N/S is circling the earth over the equator and when it is on the far side of the earth from us, the resulting small angles from the others are not what some units can handle. On my last trip north, 2006, I was using a Garmin 2720 GPS and it seemed to handle it much better. With Streets and Trips running on my laptop, the 2004 GPS dongle, had major problems in the Valdez area locating my position. Another camper next to me was running the same version software of S & T but had purchased a different GPS dongle. His set up worked much more accurately so when I returned home, before the next trip north I purchased a new dongle with the SiRF chip set. It worked much better for me as it is much more sensitive.
Gist of all this verbiage is that the signal is there in the north country, but how the GPS unit handles it is a different story. The one GPS that was giving me all the problems in the north, worked fine by the time I got south of Whitehorse YT.
If you have Nexrad weather services for your GPS, it won't work in northern Alaska from what I understand due to the satellite that broadcast that signal isn't usable by the time it reaches that far north. (perhaps below the horizon?)
Nexrad is much more common in aircraft GPS units than car ones I would guess.
On Edit: Here is a Garmin web site showing the locations of the satellites making up the US GPS system. http://www8.garmin.com/aboutGPS/ As can be seen, when the bird that crosses over Florida, heads for California and around the earth, twice a day is close and at a high angle to Alaska, so most any GPS unit will be generally accurate. However when it is on the far side of the earth, Alaska is receiving the GPS signal for latitude, from the bird over the equator, a much smaller angle to the horizon and much farther away. It takes a high quality GPS receiver to accurately triangulate that equatorial signal, which many boat and aircraft GPS units are able to do, as well as some of the top line auto units. Most electronic equipment comes in many different grades, i.e. stereo units, speaker systems, TVs, nav/com radios, etc. IMHO, GPS units are no different. My $1200 boat GPS does a much better job for me than does my first GPS I bought for my car at $150. If I am involved in an activity that can be life threating such as off shore boating or flying, I want the best navigation equipment that I can afford. But not in my RV as I can always pull over and ask for directions if need be. LOL
* This post was
last
edited 11/17/08 10:08am by joe b. *
View edit history
joe b.
South Florida, Stuart
Formerly of Colorado and Alaska
Driving a Dodge/Cummins
www.jbpacooper.com web site
http://www.picturetrail.com/jbpacooper Alaska 2004 - Alaska 2006 - Colorado photos
|
Hook
Kenai Peninsula, Alaska
Senior Member
Joined: 12/20/2003
View Profile
|
The GPS system on my boat, a Garmin, will bring me back into the Homer Harbor right to the boat slip in a solid fog. I have used it to find my fishing holes, crab pot bouys, etc. Now the Garmin system with the map system that my wife has in her Yukon GMC periodically will show her off the road but I think that is a programmers error from someone entering the wrong coordinates. There are times during startup that it takes several attempts to boot up your location, one time it was over an hour before the GPS locked on but that is very infrequent. I think for all practical purposes they work and are fairly accurate. Going back to the boat, I run twin GPS's. One a Garmin with chart plotter and another handheld Garmin attached to the consule. Both seem to work very accuratley once locked on.
Hook
Chevy 2500 4x4 CC D-Max/Allison, Supersprings,Torqlift
Summerwind 806
"Kik-n-but" 23' modified Atec, twin Yamaha 60's, full electronics,
Hewes 20' Kenai Special 50hp Yamaha, 9.9 kicker
Polaris RZR
|
big dave
Soldotna, Alaska, USA
Senior Member
Joined: 12/15/2001
View Profile
Offline
|
As far as the GPS is concerned, it works great here, it will take you within a few feet of a given set of coordinates every time, but the mapping software doesn't always match the real world. For example, there's an area along the Turnagin arm where my GPS says I'm driving in the water, and I'm off route (there's only one road). I found the same problem in South Carolina. Google Earth will show the same error.
Satellite radio won't work here, the satellites are too low in the sky.
Dave & Rose C
90 Safari Ivory 34' DP
04 Saturn VUE V6
|
joe b.
Florida
Senior Member
Joined: 08/24/2002
View Profile
Online
|
Hook, Dave or others,
Do any of you have experience with GPS topo maps in Alaska? Especially for the hand held units. I have one of the Delorme topo paper atlas books but would like to have something workable for off road hiking and fishing for navigation to find my truck afterwords. LOL I have some friends that live out on the East End Rd in Homer and have found some the roads (?) they live on don't show up on any of my GPS programs. Thinking perhaps a topo map might show their street/trail/path, etc. Does any company make preloaded SD chips with Alaska as a topo map, that could just be plugged into my Garmin? I can only find the CD version listed on the Garmin web site.
thanks,
|
|
|
big dave
Soldotna, Alaska, USA
Senior Member
Joined: 12/15/2001
View Profile
Offline
|
joe b. wrote:Hook, Dave or others,
Do any of you have experience with GPS topo maps in Alaska? Especially for the hand held units. I have one of the Delorme topo paper atlas books but would like to have something workable for off road hiking and fishing for navigation to find my truck afterwords. LOL I have some friends that live out on the East End Rd in Homer and have found some the roads (?) they live on don't show up on any of my GPS programs. Thinking perhaps a topo map might show their street/trail/path, etc. Does any company make preloaded SD chips with Alaska as a topo map, that could just be plugged into my Garmin? I can only find the CD version listed on the Garmin web site.
thanks,
I have Garmin's topo maps of the Western US and Alaska, and they work great! Though your friend's road off East End road may or may not be included, depending on when it was built. I don't know how much lag there is. Check it out on Google Earth.
|
KPSmithSr
Florissant, Mo, USA
Full Member
Joined: 05/29/2004
View Profile
Offline
|
Let me clear up a few things that are misleading on the Garmin site. The GPS satellites do not really follow the obits as shown on Garmin figure; there are no North-South (polar) or East-West (equatorial) orbits for the GPS satellites. (The slanted ones are correct.) All the orbits are slanted at 55 degrees from the equator. That is they go from the southwest to the northeast on one side of the orbit and go down from the northwest to the southeast on the other side of the orbit. There are 6 of these orbit paths with 4 GPS satellites in each orbit. At the northern points of their orbit, there will be satellites visible in Alaska.
The sensitivity of your receiver will allow you to pickup more satellites, in addition; the newer receivers can track more satellites than the older ones. (Older receivers typically had 4 channels where newer ones have 12 or even 24 channels.) GPS works on line-of-sight and normally will not track satellites close to the horizon. For example, if you were in the bay in Anchorage (sea level), a satellite passing over the equator would be less than 10 degrees above the horizon and would most likely not be tracked. (If there were a mountain in the way, it certainly would not track that Satellite.) If that satellite were heading northeast, the receiver would eventually pick it up and track it until it got low in the horizon on the other side of the orbit. It will not track satellite below the horizon since the earth blocks the signal
Sometimes the tracking program in the GPS does not initialize correctly and that can cause a bias or offset from the correct position. Normally restarting the system will correct that. Accuracy of the GPS is not only dependent on the quality of the GPS receiver but also on the position of the satellites the GPS can see. If you are in a valley and all the satellites in view are clumped together, your GPS accuracy normally is poor. The more the tracked satellites are spread in the sky, the better the GPS accuracy. Since the orbits of the satellites do not cross over the North Pole, that section of the sky will never have satellites that can be tracked, limiting the satellite availability compared to points on the earth further south. Ground based receivers in Alaska are more likely to have a problem with masking, due to the mountains, giving them fewer satellites to track. Again, those that it will see during high masking will be clumped together.
If there is something I messed up or if you have more questions, please let me know.
This site will give you a good tutorial on GPS. Click the link for the GPS Constellation to see the path of the orbits.
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html
Ken and Sue Smith
'05 Silverado 3500 LS, DRW, D/A, Sport Red
2007 Carriage Cameo 35KS3
BrakeSmart Brake Controller
|
Grey Mountain
On the rez somewhere in Indian Country
Senior Member
Joined: 08/25/2002
View Profile
Online
|
Don't need a GPS. Got a wife.
GM
2000 Southwind Storm 34N Tin Teepee
Jeep Cherokee toad
Enrolled member of the Comanche Tribe
English Bride
Bichon Frise bear killers:
Lord Shonefeld von Reginald-Friese IV.
Lady Annabelle von Lichenstein-Friese III.
|
joe b.
Florida
Senior Member
Joined: 08/24/2002
View Profile
Online
|
Thanks Ken, your answer makes more sense than mine did. LOL What's your thinking as to why Garmin, the world's largest maker of GPS units, shows the orbits the way they do? Just curious, not doubting.
Lonnie, on my last trip to Alaska in 2006, my wife flew to Colorado out of Anchorage leaving me on my own. Had to buy a new GPS with voice commands just to feel like the wife was still with me. LOL Found one that sounded somewhat like her voice. Just kept waiting for the GPS voice to say "I told you to turn right back at that crossroad."
|
KPSmithSr
Florissant, Mo, USA
Full Member
Joined: 05/29/2004
View Profile
Offline
|
Joe,
Not sure why they show what they show, I was a bit surprised. You would think they would show the orbits a little more accurately than they did. If you look at the link in the post, it gives a good description of the GPS space(satellite) and user (you and me) systems. Back in the May of 2000, a thing called Selective Availability was turned off. The result of SA being turned off is that the civilian GPS receivers are more accurate. So if you were in Alaska before May of 2000, your GPS receiver would not do as well as it does now. As they put up new satellites, the power levels have increased and that has resulted in better receiver accuracy. In addition, the satellite location accuracy has increased and that allows the receiver to calculate their location better. All in all, the GPS has been a success and continues to get better.
Good luck navigating.
|
|
|
|
