Maybe I'm just imaging things, but it seems like it is taking my nav system longer and longer to "lock on" to two or three satellites when I first start up the car.

When I picked up my TL-S a month ago, I was impressed with how well it locked on and kept contact with at least three satellites (three green bars on the display). I live in the Northeast in a very rural area so lots of open sky. Even in a blinding rainstorm with heavy cloud cover and lightning activity I still would have three green bars. And when I first backed out of my garage, it would go from no bars to green bars almost instantly. Lately, I'll have to drive five minutes or more before I get *any* satellite contact and then it is usually only two satellites (yellow bars). More often than not, I'm driving in wide open farm country on a sunny day and only see yellow bars on the display. It still tracks pretty well and I guess if I didn't see so much green the first few weeks I used it I wouldn't even care. I know sun spots and other atmospheric EMF interference can wreck havoc on GPS systems. So is anyone else in the Northeast having trouble with their navs?

 

I live in Northborough and I have been into worcester, and Boston and I have not had that problem. Maybe I have not noticed it. I well check it out when I get my car back.

 

Never had that problem in my TL-S or my former 99TL!
Maybe you have a poor connection between the unit and the antenna!

:-jon

 

pianoman41--I had the same concerns you did. Mine worked great the first month I had it but then the yellow bars began to show about 50% of the time but with no loss in tracking or operation. However, when first starting out, the street name would not be displayed until I drove about 1/2 mile then all was well. It cleared up after a month or so and now always shows the green bars and street name right away. Apparently it has something to do with the atmosphere or satellite positions, if the month as an "r" it, etc. Anyway I believe this is normal.

However, the 3 green bars don't indicate how many satellites your vechile is seeing. It indicates signal strength. It works like this: no bars--NO signal; 2 YELLOW bars--weak signal; 3 GREEN bars--Strong signal.

If you wish to see how many satellites your vehicle is "seeing," do this to reach the hidden "Diagnosis Menu": (but don't change anything--just view!)

Turn ignition to ON. (No need to start the engine but it works while running too.)

Press OK on the Disclaimer screen. (Important!)

Press and HOLD the MENU button.

While still holding the MENU button, press and HOLD the MAP/GUIDE button.

While still holding those two buttons, Press and HOLD the CANCEL button.

You should be pressing and HOLDING all three buttons at the same time. HOLD all 3 buttons for about 3-5 seconds and the "Diagnosis Murder err...Menu" should display. You can now let go of the buttons.

One of the menu choices is GPS. Press GPS and the screen will display a cool representation of up to 8 satellites and their position in the sky. On the right side of the screen (inside the circles) the yellow dots are the satellites your car is actually in contact with. The blue dots are the satellites your car is searching for. (The left side of the screen shows graphics of the 8 satellites--the yellow ones you can see, the black you cannot.) It should connect with all 8 after a few moments. You can see each satellite change to yellow as it finds each one. Mine usually connects with all 8.

There are lots of other menu choices in this Diagnosis Menu too so have fun but don't change anything, just look at the screens as I have no idea how to get the settings back to their default.

Hope this helps!

 

OK, I write software for GPS sensors for aircraft for a living, so let's see if I can contribute a little towards this discussion.

The slow acquisition problems that occur may be the result of expired almanacs. GPS receivers use almanacs downloaded from the satellites as part of their data stream to predict the positions of satellites given a position and time. Thing is, the almanacs have a lifespan of 1 week, after which a new almanac must be downloaded. A complete almanac download takes about 12 minutes (the GPS data stream is extremely slow--only 50 bits per second!). Without a valid almanac, the GPS receiver wouldn't know which satellites to look for.

Picture this: You've been driving around and the GPS is tracking fine. You pull up into your garage and turn the car off. During that time, the almanac expires. The next morning, you turn on your navi and it's completely lost! It must then search the sky for any valid satellite and download a brand new almanac before it can navigate. This process will probably take about 15 minutes.

Yes, this happens even for aircraft GPS's.

By the way, the GPS satellite signal is very weak, and is easily obstructed by buildings and foliage. Parking in a garage or carport will obstruct the signals until you drive out.

 

By the way, have any of you ever driven through a tunnel and the signal is lost, of course? As I understand it, the system keeps working by using "dead reckoning" and makes an educated guess as to where you are until you have a signal again. It works great--I was impressed. Can you expound on this daverman?

 

Yep, in addition to using the GPS signal, the Navi also monitors the vehicle speed sensor (VSS) signal that drives your speedometer to determine your groundspeed. It combines this information with a yaw rate sensor which senses how rapidly you're turning.

So, when the GPS signal is lost, speed + direction will give you your current position based on your last known position. Simple, and it works! You can drive through tunnels and covered parking lots and the system will track reasonably well.

Another trick that the Navi uses is map-snapping. Whenever you're traveling at some speed close to a road, the Navi software will "snap" you to that road. This takes care of errors in the GPS signal and the position estimation. This works especially well when you make a 90-degree turn at an intersection.

Another tidbit: During normal driving, the Navi actually uses the VSS+yaw rate sensor as its primary navigation source, and uses the GPS signal occasionally to correct its position. Don't tell anyone!

 

This is just like your PCS phone. When you turn it on everyday, the phone has an MRU or a "most recently used" list that might contain Kansas City, Overland Park, Olathe, St. Jo, St. Louis, etc. It can find service quickly by first scanning the MRU and getting a hit in just seconds.

If you turn off your phone, get on an aircraft, fly to Minneapolis, when you get off the plane and turn on your phone, it checks the MRU first, doesn't fine your "friendly" systems, then starts scanning the PRL (preferred roaming list) until it finds Minneapolis. Depending on the phone's scanning algorithm and the structure of the PRL, this could take several long minutes until you "find service."

I wonder what kind of MRU the Navi has. I know GPS has something like this because they always say if you go to China (way, way far away) you might have trouble.... read here for more GPS info.

 

I'm a techno-geek extraordinaire so you know I already checked out all the set-up menus. However, in the FSM when it discusses the navi it says that three yellow bars means it has only made contact with two satellites, and futher explains that this means it can give an accurate lat and long, but cannot do elevation (is that right daverman?). Once it picks up the third satellite, the three bars turn green and now it can correctly calculate lat,long and elevation. So green does mean 3+ (up to 8 I believe at one time).

 

Okay, so maybe this is contributing to my problem. Since my place of work is only 7 minutes from my house (yeah, long commute!), if my almanac expires and then it tries to fire up the next day looking for it, I'm not giving it enough time to find and download the new one? And if I don't do any other driving for three days straight (just back and forth to work), then I never get the new almanac because it can't complete the download?

Now *that's* going to be a cool excuse to use on the wife to go out for a drive: "But honey, I've gotta go out and update my alamanc. I'll be back in an hour!!"

I like it..........

 

Interesting...I didn't know that. I was looking at the Acura Navi manual (page 48) and it simply states "strong" or "weak." But that's good to know!

 

I don't have the nav but I was wondering, shouldn't there at all times be at least 3 satellites overhead for triangulation???

 

I'm probably wrong but wouldn't the triangle be the two satellites and me?

 

Correct. Satellite 1 to ground and satellite 2 to ground plus satellite to satellite gives you triangulation. Adding the third gives the third dimension for elevation.

 

The GPS satellite constellation also contains the capability to switch into a 'P(Y)' mode of operation which requires the use of special keys to continue to operate without loss of accuracy. In this mode, false information is embedded into the system to purposely confuse the GPS receivers which do not have the special keys. All this was intended for wartime use by the government which btw as I understand it can be defeated by the use of a 'differential' reference signal from a ground station someplace. Does anyone know if the GPS satellite constellation is ever being switched into/out of this mode of operation and if so, how often?

 

I don't have that problem here in Boston and in the Metro West area.

 

Great give me something else to look at and worry about

I've never even noticed how many satalites mine gets. The NAV is as accurate as I could imagine.

I'm in NJ.

 

I believe that feature has been turned off, for the time being.

During the Gulf War, they turned it off since the military was relying on commercial GPS receivers -- they could produce enough secret-decoder versions fast enough. After the Gulf War was over, they scrambled again. My dad had a receiver on his boat, and you could definitely see the difference in accuracy.

Anyhow, about a year or two ago the shut off the scrambling. Why? There were plenty of "Differential GPS" systems on the market that used a fixed ground point of reference to correct for the scrambling. In fact, the Coast Guard ran a number of Diff. GPS broadcasting stations. Finally, the feds decided it was dumb to have one branch of the military defeating the scrambling on another branch, and they turned it off. As far as I know, it's still off.

 

Correct me if i'm wrong but i think you need 4 satellite signals to find your exact location in 3-D space. The reason is that 3 sats will give you the trilateration but will have to estimate your altitude. Also, you need the 4th satellite to give you time correction information needed for accuracy.

amcl

 

You are correct. The Navi (and other ground-bound GPS's) can use 3 satellites plus your last known altitude to estimate your position on the ground. 4 satellites is the minimum required for 3D positioning. Remember that there are 4 variables to be found: the three axes of position plus time. More satellites will reduce your estimated position error, although it's their position in the sky that affects position error the most.

Nick: You're referring to SA (Selective Availability). The Dept. of Defense has switched SA off for quite a while now. P(Y) code is encrypted, and decrypting receivers are strictly for the military. No commercial receivers are available.

pianoman: Yep, that's probably what's happening. You need to drive around for about 15-20 minutes for a complete almanac to be downloaded. Some GPS receivers extrapolate the almanacs well beyond their 1 week lifespan with good results, but apparently our Navi doesn't.

A bit of trivia: aviation GPS receivers use the input from an encoding altimeter as an additonal "satellite" which provides height above sea level.

 

OK, while we're on the subject, this has always bothered me.

The nav system does not seem to be particularly accurate in my car. Many times, when I pull out of the garage, it puts me on the wrong street in my neighborhood. I understand this is probably because I don't see the satellites right away, but it takes it a couple of minutes to think I'm actually driving on the right road. I thought it received a constant signal, which means as soon as I get out on the main road - which is wide open, no trees, buildings, etc. - it would correct itself.

What's more annoying is that when I am on the freeway, many times the nav system shows me as being on the access road that runs parallel to the freeway. This doesn't seem to correct itself quickly or at all - I have run for 10-15 miles on the freeway and it always says I'm on the access road.

Does anyone else see this with their system, or could I have a problem with my system?

 

This is a very common problem with the Navi's. The culprit is most likely the map-snapping feature that snaps you to the nearest parallel road to your last estimated position. When that happens to be a frontage road, that's what you get.

The problem is made worse when you drive off a main road into an unmapped region (like your driveway). The snapping feature sometimes won't let you leave the road soon enough, so your position is compromised.

Also, reversing your car sometimes degrades your position. When you reverse, the speed sensor is not functional, so the Navi must estimate your position, usually with questionable results. Driving a straight line in reverse seems to be the worst. Full-tilt reverse turns seem to be well-estimated.

Most of the time, driving on a mapped road for about 1/2 mile and then making a right-angle turn onto another road fixes your position error. If you get on the highway before this happens or after driving a long straight road, the Navi may think you are turning onto a parallel road.

You may be able to fix the problem by using the Setup/Position Correction option just before you drive onto a mapped road.

 

1. The Acura Care people consulted Alpine (on my behalf) and said to never use the position correction option. (I know this sounds nuts -- I said, "Why did you put this in the manual and as a user option..." They didn't respond, they just said not to use it.

2. The position correction has an unknown "radius of correction" -- I was given about three different stories about the radius from the adjustment point that the positional correction would modify. Another rep. said that the adjustment altered the entire map, but I've checked this out, and this isn't the case.

3. Differential GPS -- a local ground station puts out a very accurate correction signal ( the ground station is stationary, so it is not moving -- it does know where it is). Units that can use this technology, have accuracies good enough to check for fault slippage (ground movement). Our NAVI units DO NOT use Diff. GPS, so the mean error (positional error) can vary from about 50 to 200 feet -- this enough to allow the unit to "latch" on to a parallel road. I've seen this behavior come and go, depending on area and random factors.

4. You are quite correct about the 90 degree turns helping the system align the sat. info with the NAVI’s map data. In fact, the "cool" reset procedure to align a unit that has been turned off, requires the user to make a 90 degree turn after driving dead straight for ONE mile. Then vary the driving. (Sorry, for this -- you won't need to ever do this unless your battery is disconnected for more than 20-30 minutes…)

BTW -- some of the dealers just calibrate the units with the car sitting in the lot (not moving). The Acura Care/ Alpine Engineers suggested the 1 mile straight, 90 degree turn, and varied driving as the #1 way to get the unit working after a hard reset! (There are some more minor details, but I've already gone way too far).

 

I think this is bogus. I've used the correction feature several times with good results.
I can't determine the radius of correction for certain, but it seems to be about 500 ft. or so. Actually, corrections seem to be made only once every 2 seconds or so.

What did the rep mean by "altering the entire map"?
You are correct, DGPS is not used. Instead, the Navi depends on the speed and yaw rate sensors to provide short-term accuracy, and GPS only for long-term accuracy.

Maybe the Navi can snap to a road based on your speed... say, if you're traveling 65 MPH on a 35 MPH frontage road, it will select the highway instead... But on second thought, the way we drive... forget about it
I'm surprised that the dealers do not calibrate the yaw rate sensor sensitivity. As you can read from my previous posts, I had to manually tweak the yaw rate damping to prevent my position icon from jiggling all over the place.

 

I've posted this link before but you probably missed it so I'll post it again: http://joe.mehaffey.com/ Everything that has been talked about here you'll find there.

If you want to be as smart as daverman about GPS, everything you can possible want to know about GPS is on this website, these guys know it all. Most of their info relates to portable handheld GPS but it's the same concept and the same satellite system. I caution you about receiving info from Alpine and/or Acura about the Navi. Unless you're talking to the Chief Scientist or the Lead Engineer or the Project Manager, don't count on getting the correct answer to your question(s). They don't know as much as GPS as you think.

Do the research for yourself, it's all there: SA (isn't on, why it was turned off, how large was the error), almanacs, 4 satellites (for 3D nav), differential GPS, dead-reckoning, satellite orbit patterns (where are the satellites at any one time), signal strength (how strong does the signal really need to be), daylight savings time/internal clocks/GPS time/World time zones, where these maps come from, what happens when a satellite goes down, does weather affect GPS, the future of GPS, etc.

 

Fascinating information! My Nav always has the 3 green bars showing, but the system is not too smart. I keeping asking for a route to the moon and it doesn't know!