| Author |
Message |
TLoewenberg
Guest
|
 Posted:
Mon Oct 17, 2005 12:08 am Post subject:
GPS Satellite Searching in Connecticut |
|
|
I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to track
is if I pull over and stop. Sometimes, more often than not, it doesn't seem
to make any difference. At first, I thought it a problem with the many
trees in this state. Now, I'm starting to wonder if it's the Ct sky or tree
density or lousey State coverage. If you've had similar experience I'd be
interested. The Garmin is about 6 years old; could that be a contributor?
Thanks,
TL |
|
| Back to top |
|
 |
Darren Griffin - PocketGP
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
TLoewenberg wrote:
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an
Axim x30 or Dell 8600. My problem is that both take forever to find
enough satellites to track. Usually, the only way either will find
enough to track is if I pull over and stop. Sometimes, more often
than not, it doesn't seem to make any difference. At first, I
thought it a problem with the many trees in this state. Now, I'm
starting to wonder if it's the Ct sky or tree density or lousey State
coverage. If you've had similar experience I'd be interested. The
Garmin is about 6 years old; could that be a contributor? Thanks,
TL
|
More likely your vehicle's windscreen is the culprit, athermic coatings reek
havoc with satellite signal reception.
--
Darren Griffin
PocketGPSWorld - www.PocketGPSWorld.com
The Premier GPS Resource for News, Reviews and Forums
Creators of the free UK Safety Camera POI |
|
| Back to top |
|
|
Steve Calvin
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
TLoewenberg wrote:
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to track
is if I pull over and stop. Sometimes, more often than not, it doesn't seem
to make any difference. At first, I thought it a problem with the many
trees in this state. Now, I'm starting to wonder if it's the Ct sky or tree
density or lousey State coverage. If you've had similar experience I'd be
interested. The Garmin is about 6 years old; could that be a contributor?
Thanks,
TL
|
hm... interesting... I can't really think of what would cause that.
Windshield maybe? (dunno, just a wag) I travel through Ct. on my way to
Rhode Island for tuna fishing and also sometimes when I head up to Maine
for whitetail and have never had that problem with my 76CS.
Maybe try an externally mounted antenae?
--
Steve
Never read the fine print. There ain't no way you're going to like it. |
|
| Back to top |
|
|
Pete LaFlamme
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
Just drove from Dallas Texas to Manchester Connecticut. While in
Connecticut (4 days) I never had a problem finding satellites.
I have a Garmin 2620 with the latest software (not that should make a
difference) North America City Navigator, version 7.
"TLoewenberg" <termarl@msn.com> wrote in message
news:gaedneH5doPgNM_eRVn-pA@myeastern.com...
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to
track is if I pull over and stop. Sometimes, more often than not, it
doesn't seem to make any difference. At first, I thought it a problem with
the many trees in this state. Now, I'm starting to wonder if it's the Ct
sky or tree density or lousey State coverage. If you've had similar
experience I'd be interested. The Garmin is about 6 years old; could that
be a contributor?
Thanks,
TL
|
|
|
| Back to top |
|
|
Sam Wormley
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
Jack Yeazel wrote:
| Quote: |
"Wayne R." wrote:
To initialize the unit, it needs uninterrupted signal from several
satellites to get the thing initialized. I'm not sure it's a fixed
period or period that's model specific, but moving through trees
during this period constantly resets the buffer (whatever) and
restarts the acquisition process.
Once the initialization is complete, brief interruptions are taken in
stride. (That's one reason why cold start times are longer than warm
start.)
This is the correct answer... In order to lock on to each individual
satellite, the receiver must receive 30 Seconds of PERFECT navigation
data from each satellite... Motion of the receiver is most often the
cause of the long lock times...
The navigation data is repeated every 30 seconds, so with a perfect view
of the sky (depending where you turn the unit on during the 30-second
cycle) it could take 31 to 61 seconds to get a 2D or 3D lock... That's
why Garmin states it as "45 seconds, typical"...
|
Welcome back! :-) |
|
| Back to top |
|
|
peter
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
Jack wrote:
| Quote: | The navigation data is repeated every 30 seconds, so with a perfect view
of the sky (depending where you turn the unit on during the 30-second
cycle) it could take 31 to 61 seconds to get a 2D or 3D lock... That's
why Garmin states it as "45 seconds, typical"...
|
What am I missing? Once the receiver locks onto the signal from a
satellite by correlating with the correct spreading code it can start
reading the data link which, as you state, repeats with a 30 second
frame period. So the receiver can store the incoming data until it can
identify the frame structure and therefore properly interpret the data.
Since a frame of the message takes only 30 seconds that amount of data
should be sufficient for the receiver to start its processing and
determine a position fix. I don't see why it would ever take the 61
seconds stated above in the absence of data errors.
Actually only 18 seconds (3 subframes) of the 30 second data message
are required to be received for the unit to use that satellite for a
position fix since the other two subframes have almanac data on the
other satellites (with a superframe of 24 frames providing complete
almanac data every 12.5 minutes). So if we're lucky in our timing of
turning on the receiver we might be able to make do with less than 30
seconds of error-free data, but I don't see why we should ever need
more than the 30 second frame length plus the processing time. |
|
| Back to top |
|
|
Jack Yeazel
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
"Wayne R." wrote:
| Quote: | To initialize the unit, it needs uninterrupted signal from several
satellites to get the thing initialized. I'm not sure it's a fixed
period or period that's model specific, but moving through trees
during this period constantly resets the buffer (whatever) and
restarts the acquisition process.
Once the initialization is complete, brief interruptions are taken in
stride. (That's one reason why cold start times are longer than warm
start.)
|
This is the correct answer... In order to lock on to each individual
satellite, the receiver must receive 30 Seconds of PERFECT navigation
data from each satellite... Motion of the receiver is most often the
cause of the long lock times...
The navigation data is repeated every 30 seconds, so with a perfect view
of the sky (depending where you turn the unit on during the 30-second
cycle) it could take 31 to 61 seconds to get a 2D or 3D lock... That's
why Garmin states it as "45 seconds, typical"...
--
Jack
Get general GPS information at: http://www.gpsinformation.net/ |
|
| Back to top |
|
|
Stan Gosnell
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
"TLoewenberg" <termarl@msn.com> wrote in
news:gaedneH5doPgNM_eRVn-pA@myeastern.com:
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim
x30 or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to
track is if I pull over and stop. Sometimes, more often than not, it
doesn't seem to make any difference. At first, I thought it a problem
with the many trees in this state. Now, I'm starting to wonder if
it's the Ct sky or tree density or lousey State coverage. If you've
had similar experience I'd be interested. The Garmin is about 6 years
old; could that be a contributor? Thanks,
TL
|
Where are the receivers? They have to have a good view of the sky. You
need to make sure they're well into the windshield, and that the
windshield doesn't have metallic tinting in it. Some windshields will
completely block GPS signals, as well as those used by toll roads to
detect the quick-pay thingies. Usually there is a bare spot right behind
the rearview mirror, though.
--
Regards,
Stan
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin |
|
| Back to top |
|
|
Wayne R.
Guest
|
| Posted:
Mon Oct 17, 2005 12:08 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
On Sun, 16 Oct 2005 15:26:53 -0400, "TLoewenberg" <termarl@msn.com>
wrote (with clarity & insight):
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to track
is if I pull over and stop.
|
To initialize the unit, it needs uninterrupted signal from several
satellites to get the thing initialized. I'm not sure it's a fixed
period or period that's model specific, but moving through trees
during this period constantly resets the buffer (whatever) and
restarts the acquisition process.
Once the initialization is complete, brief interruptions are taken in
stride. (That's one reason why cold start times are longer than warm
start.)
| Quote: | Sometimes, more often than not, it doesn't seem
to make any difference. At first, I thought it a problem with the many
trees in this state. Now, I'm starting to wonder if it's the Ct sky or tree
density or lousey State coverage.
|
If you're keeping the unit on the dashboard, as you twist around under
the tree cover, you're limiting sky view even more, and just
complicating the initialization period with more resets. Consider a
rooftop antenna, and don't move for a couple of minutes when you start
it up - you'll get a stable lock quickly.
| Quote: | If you've had similar experience I'd be
interested. The Garmin is about 6 years old; could that be a contributor?
|
Like most digital equipment, they either work fine or they're
obviously malfuncitioning. Time spent out of the the box only matters
if it's getting a beating too. |
|
| Back to top |
|
|
Jack Yeazel
Guest
|
| Posted:
Mon Oct 17, 2005 5:09 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
I'm gonna' get into trouble answering this question without Sam
Wormley's help!
-But as I understand it, all navigation messages start at the same time
(world wide)... Thus if you turn on a receiver one second after the
navigation messages start, the first 30 seconds will be rejected but the
second 30 seconds can be received error free which equals 61 seconds to
lockon...
peter wrote:
| Quote: |
Jack wrote:
The navigation data is repeated every 30 seconds, so with a perfect view
of the sky (depending where you turn the unit on during the 30-second
cycle) it could take 31 to 61 seconds to get a 2D or 3D lock... That's
why Garmin states it as "45 seconds, typical"...
What am I missing? Once the receiver locks onto the signal from a
satellite by correlating with the correct spreading code it can start
reading the data link which, as you state, repeats with a 30 second
frame period. So the receiver can store the incoming data until it can
identify the frame structure and therefore properly interpret the data.
Since a frame of the message takes only 30 seconds that amount of data
should be sufficient for the receiver to start its processing and
determine a position fix. I don't see why it would ever take the 61
seconds stated above in the absence of data errors.
Actually only 18 seconds (3 subframes) of the 30 second data message
are required to be received for the unit to use that satellite for a
position fix since the other two subframes have almanac data on the
other satellites (with a superframe of 24 frames providing complete
almanac data every 12.5 minutes). So if we're lucky in our timing of
turning on the receiver we might be able to make do with less than 30
seconds of error-free data, but I don't see why we should ever need
more than the 30 second frame length plus the processing time.
|
--
Jack
Get general GPS information at: http://www.gpsinformation.net/ |
|
| Back to top |
|
|
matt weber
Guest
|
| Posted:
Mon Oct 17, 2005 5:33 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
On Sun, 16 Oct 2005 15:26:53 -0400, "TLoewenberg" <termarl@msn.com>
wrote:
| Quote: | I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to track
is if I pull over and stop. Sometimes, more often than not, it doesn't seem
to make any difference. At first, I thought it a problem with the many
trees in this state. Now, I'm starting to wonder if it's the Ct sky or tree
density or lousey State coverage. If you've had similar experience I'd be
interested. The Garmin is about 6 years old; could that be a contributor?
Thanks,
TL
Where do you put the GPS when you drive? It is important they have |
good view of the sky, and are able to watch the same, good sized
portion until they get a lock. Unless you put the GPS all the way
forward up against the windshield, you usually cannot get an initial
lock. I don't think a GPS 3+ supports an external antenna, but on the
models that do, well I have a velcro strip all the way at the front
where the dashboard meets the windshield, and that's where I put
external antennae. Provides a veiw of about 70% of the sky, anything
more than about 65 degrees above the horizon can be seen, regardless
of change of direction.
In addition, the internal battery (on the PCB, not the AA cells that
power the GPS III) may have failed. This causes the unit to fail to
retain current almanac information, and that slows down initial
acquisition not a little, a lot..... |
|
| Back to top |
|
|
Dale DePriest
Guest
|
| Posted:
Mon Oct 17, 2005 6:31 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
peter wrote:
| Quote: | Jack wrote:
The navigation data is repeated every 30 seconds, so with a perfect view
of the sky (depending where you turn the unit on during the 30-second
cycle) it could take 31 to 61 seconds to get a 2D or 3D lock... That's
why Garmin states it as "45 seconds, typical"...
What am I missing? Once the receiver locks onto the signal from a
satellite by correlating with the correct spreading code it can start
reading the data link which, as you state, repeats with a 30 second
frame period. So the receiver can store the incoming data until it can
identify the frame structure and therefore properly interpret the data.
Since a frame of the message takes only 30 seconds that amount of data
should be sufficient for the receiver to start its processing and
determine a position fix. I don't see why it would ever take the 61
seconds stated above in the absence of data errors.
Actually only 18 seconds (3 subframes) of the 30 second data message
are required to be received for the unit to use that satellite for a
position fix since the other two subframes have almanac data on the
other satellites (with a superframe of 24 frames providing complete
almanac data every 12.5 minutes). So if we're lucky in our timing of
turning on the receiver we might be able to make do with less than 30
seconds of error-free data, but I don't see why we should ever need
more than the 30 second frame length plus the processing time.
|
You are correct. There are 3 6 second packets and it must receive all
three to be ok. It is easy to corrupt the data however, since driving
under a wire while receiving the data will interrupt the flow resulting
in a 30 second delay. In the worst case with no interruptions it can
take 5.99 seonds of throwaway data since it didn't start exactly on the
correct interval, 12 second of data, 12 seconds of nothing (the good
data is repeated only every 30 seconds(, and 6 seconds more. Thus it can
take 36 seconds to get the data if it all comes the first time.
Dale
--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs |
|
| Back to top |
|
|
TLoewenberg
Guest
|
| Posted:
Mon Oct 17, 2005 7:27 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
Hmmm, on placement, I try to position the gps as far forward on the dash as
possible. I also have a ram mount that positions the gps further back but
with the antenna still under the windshield. How would I know (or find out)
if the pcb battery has failed? Is it user replaceable? If the battery is
okay, how long does the III+ retain the almanac data? As for the small
bluetooth gps, I place it all the way forward in the center of the
windshield. The bluetooth gps is a Dell, who has agreed to replace it under
warranty. If the new one, acts the same way, I can only assume too many
trees and/or a gps unfriendly windshield.
Thx
TL
"matt weber" <mattheww50@cox.net> wrote in message
news:42s5l1l2t7vdjs0p1b0hbs940d4ckpuidm@4ax.com...
| Quote: | On Sun, 16 Oct 2005 15:26:53 -0400, "TLoewenberg" <termarl@msn.com
wrote:
I have a Garmin 3+ and a NavTeq bluetootch gps that I use with an Axim x30
or Dell 8600. My problem is that both take forever to find enough
satellites to track. Usually, the only way either will find enough to
track
is if I pull over and stop. Sometimes, more often than not, it doesn't
seem
to make any difference. At first, I thought it a problem with the many
trees in this state. Now, I'm starting to wonder if it's the Ct sky or
tree
density or lousey State coverage. If you've had similar experience I'd be
interested. The Garmin is about 6 years old; could that be a contributor?
Thanks,
TL
Where do you put the GPS when you drive? It is important they have
good view of the sky, and are able to watch the same, good sized
portion until they get a lock. Unless you put the GPS all the way
forward up against the windshield, you usually cannot get an initial
lock. I don't think a GPS 3+ supports an external antenna, but on the
models that do, well I have a velcro strip all the way at the front
where the dashboard meets the windshield, and that's where I put
external antennae. Provides a veiw of about 70% of the sky, anything
more than about 65 degrees above the horizon can be seen, regardless
of change of direction.
In addition, the internal battery (on the PCB, not the AA cells that
power the GPS III) may have failed. This causes the unit to fail to
retain current almanac information, and that slows down initial
acquisition not a little, a lot..... |
|
|
| Back to top |
|
|
Steve Calvin
Guest
|
| Posted:
Mon Oct 17, 2005 7:42 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
TLoewenberg wrote:
| Quote: | Hmmm, on placement, I try to position the gps as far forward on the dash as
possible. I also have a ram mount that positions the gps further back but
with the antenna still under the windshield. How would I know (or find out)
if the pcb battery has failed? Is it user replaceable? If the battery is
okay, how long does the III+ retain the almanac data? As for the small
bluetooth gps, I place it all the way forward in the center of the
windshield. The bluetooth gps is a Dell, who has agreed to replace it under
warranty. If the new one, acts the same way, I can only assume too many
trees and/or a gps unfriendly windshield.
Thx
TL
Gawd, top postint sux |
--
Steve
Never read the fine print. There ain't no way you're going to like it. |
|
| Back to top |
|
|
Sam Wormley
Guest
|
| Posted:
Mon Oct 17, 2005 7:44 am Post subject:
Re: GPS Satellite Searching in Connecticut |
|
|
peter wrote:
| Quote: |
What am I missing? Once the receiver locks onto the signal from a
satellite by correlating with the correct spreading code it can start
reading the data link which, as you state, repeats with a 30 second
frame period. So the receiver can store the incoming data until it can
identify the frame structure and therefore properly interpret the data.
Since a frame of the message takes only 30 seconds that amount of data
should be sufficient for the receiver to start its processing and
determine a position fix. I don't see why it would ever take the 61
seconds stated above in the absence of data errors.
Actually only 18 seconds (3 subframes) of the 30 second data message
are required to be received for the unit to use that satellite for a
position fix since the other two subframes have almanac data on the
other satellites (with a superframe of 24 frames providing complete
almanac data every 12.5 minutes). So if we're lucky in our timing of
turning on the receiver we might be able to make do with less than 30
seconds of error-free data, but I don't see why we should ever need
more than the 30 second frame length plus the processing time.
|
Before a receiver can use a satellite as part of the position,
velocity, time (PVT) solution, it must verify that it has current
ephemeris data for that satellite. The ephemeris data is transmitted
every 30 second.
Each satellite transmits only its own ephemeris data, not to be
confused with every satellite transmitting the almanac data for the
whole constellation every 12.5 minutes.
A correlator is assigned a PRN code based on almanac information,
and may "latch onto" the appropriate satellite signal immediately,
but need to make sure it has the current ephemeris data to be of
much help.
All correlators my not grab their respective satellites at the
same time and my have to wait for the next 30 second interval.
Worse yet, you may drive under a tree or otherwise encounter
an obstruction when the ephemeris data was being grabbed... and
may have to try again.... and again.... and...
See GPS User Equipment Introduction - Sept 1996 (PDF Format)
http://www.navcen.uscg.gov/pubs/gps/gpsuser/gpsuser.pdf |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in