Lost satellite reception downtown

Lots of vertical obstructions and reflections of satellite signals.

You can get external an antenna if you plan on spending lots of time there and want to have your 350 working more than it did on your visit.

Thank you, have you used an external antenna in this type of situation before?

Or you can have your wife (or husband ... need to be equal opportunity here ) stand out the sunroof, or on the roof itself, holding your GPS high in the air!

I agree and I've used an external antenna for years going back to my StreetPilot Color Map... As kch50428 indicated, this is an urban canyon. The GPSr really needs line of sight contact with at least 3 satellites to provide a fix. Sitting on the dash in open terrain, the GPSr gets a fairly good view of the sky looking up and forward and to the sides, often seeing 6-9 birds. Depending on the slope of the windshield, there is a certain shadow to rear unless you drive a convertible. With an external antenna, you may see 10-12 birds. Put tall buildings to either side and the view of the sky shrinks considerably. An external antenna may help, but depending on the constellation at any given time, a narrow view of the sky looking up through the slot of the buildings may not see enough satellites to get a fix.

Many GPSrs have a way to display what satellites it sees. On my nüvi 750's main screen, if I press and hold the signal strength meter on the upper left of the main screen for about 3 seconds I see a graphic representation of the current constellation. The red dot on the outer ring represents direction of travel at the horizon, the inner ring represents a vertical cone view of 45°. The ∙ in the center represents straight up. North is at the top of the ring. The graph to the right shows the signal strength of each bird it sees. Note: This screen also shows the current position of the Sun and the Moon. As the satellites pass in orbit, the constellation constantly changes with some dropping off one horizon and others coming into view on another. Birds that should be in view are known to the GPSr by virtue of the inter-satellite communication but will be grayed out on the screen if something is blocking the view and their signal strengths are too low.

To illustrate this, set your GPSr on a picnic table out in the yard with a good view of the sky. Look at this screen and then start stacking soda cans to one side and watch the signal diminish on those where the cans block the line of sight. You may also observe that a strategically placed can may actually boost the signal of many of the satellites since it is acting as a reflector that enhances the reception.

The bottom line is that an external antenna will improve your GPSr's ability to see a bigger chunk of the sky, but there may be times that there are too many obstructions to overcome.

As is the case in tightly packed downtown areas of cities that have lots of tall buildings. Chicago is only one.

Just try to plan for it and don't panic.

Newer gps receivers that have newer chipsets work better too. A while agao SIRF III chipsets for example had faster acquiring times and seemed to hold up to more interference from things overhead. I'm not sure what the latest chips are and what would be in your model of gps.

Thank you for your answers. I was kind of upsetting when I was trying to get out of downtown and not really knowing which way to go. I really rely on my GPS now and when it doesn't work it is a problem. Driving around the streets just trying to figure things out just doesn't work for me know. My GPS is too important.

Thanks. That's an excellent, clear explanation of reception problems. Also, I didn't know how to access the satellite screen on my nuvi 750 until now!

Bob

Last year I was in downtown Chicago with my c530. Got out of the car and started walking. Sure enough, on certain streets I would loose the signal and then it would come back. Not sure if the greater signal strength from an external antennae would help, but as far as position, inside or outside the car didn't make a difference.

Not a great idea. Buy a paper map for sure if you ever plan on driving in Boston.

Between the buildings, tunnels, and multi-level roads & crossings you'll get stuck in a infinite toll-loop as well as never get anywhere.

Been there, done that, won't ever do it again!!

The satellite signal will also bounce off those buildings resulting in reduce precision.

It is scary in a strange city and your Garmin is giving you grief to say the least. Or when you know you are going the right way and it says " make a u turn your going the wrong way". That will give you a thrill.

I hate it when it does that. The best advice I think I have read and agree with is don't freak out. Just keep driving, relax and it will eventually work out. If you are in a hurry, forget about it until you get your bearings. You can have an accident if your stress level goes up so you have to remember one thing " IT IS WHAT IT IS ".

A back up when traveling is a good idea, although I rarely have one myself.

Thank you for such a great explanation

Let me also add that reflected signals travel a farther distance (and get delayed), and that induces errors (because the GPS uses the latency of the signal from the satellite to calculate its location).