Which of these 3 GPS Receivers would be best?

thepunkerguy · 07-13-2007, 11:24 AM

Alright, well the receiver I have been using (came with MS Streets and Maps 2006) just doesn't work well enough for me. It seems to take too long to initially lock onto satellites, sometimes it doesn't even connect until I am half way to my destination, even when sitting right on my dash. So Looking around I have narrowed my choices down to these three receivers. What do you guys think will be the best one to use? I want the fastest locking one possible and i want it to be very reliable.I will be mounting it in my dash just below the top of the dash, it will only be covered by a thin layer of plastic from the dash. If you recommend any others, let me know them too. I will be using it with StreetDeck/MapPoint so i need to make sure they work well with that too.

1. GlobalSat BU-353 http://www.amazon.com/GlobalSat-BU-3...339876&sr=1-11

2. Holux GR 213 Sirf Star III GPS http://www.amazon.com/Holux-mouse-re...339876&sr=1-12

3. Navibe GM720 Water-Proof USB Mouse GPS Receiver - SiRF Star III(WAAS Enabled) http://www.amazon.com/Navibe-GM720-W...339876&sr=1-13

- Mike

DarquePervert · 07-13-2007, 11:32 AM

http://www.mp3car.com/vbulletin/faq-...-receiver.html

Asking "What is the best?" is inane.
You're asking for people's opinions as to what is best, so you're going to get multiple answers, most of them different.
I have a BU353 and am very happy with it.

mezz64 · 07-13-2007, 11:33 AM

Go with the GlobalSat, i've got one installed just below the dash and always get at least 7 sats. Never had a problem with it.

thepunkerguy · 07-13-2007, 11:48 AM

Anyone used or know anything about the Navibe GM720? It seems to have the same chipset as the GlobStat but is also WAAS Enaled, incase i ever need it. And its less expensive. Any opinions on that one?

ekaz · 07-13-2007, 01:59 PM

FYI....the Globalstat is WAAS enabled.

nobb · 07-13-2007, 08:00 PM

I have the Streets and Trips GPS and I have noticed that sometimes it has a hard time locking on when moving. For those times that you mentioned your gps wasnt locking on...did you leave your car stationary to give the unit some time to lock on? When stationary, I notice that the unit will lock on in maybe 10-20 seconds.

thepunkerguy · 07-13-2007, 10:17 PM

Quote: Originally Posted by nobb

I have the Streets and Trips GPS and I have noticed that sometimes it has a hard time locking on when moving. For those times that you mentioned your gps wasnt locking on...did you leave your car stationary to give the unit some time to lock on? When stationary, I notice that the unit will lock on in maybe 10-20 seconds.

Yeah, i always usually sit still for a bit before i start going
- Mike

techfire · 07-13-2007, 11:12 PM

Arguably, the three most important factors to consider when buying a GPS receiver for use with a car pc are:

Sensitivity: measured in dBm, not be be confused with dBW (further away from zero is better)
Acquisition - How well can it begin to lock on to satellites
Tracking - How well it can stay locked on to satellites

TTFF - Time to first fix: measured in seconds (lower is better)
Cold TTFF - Usually > 4 hours since last use of the GPS
Warm/Hot TTFF - Usually 0-4 hours since last use

Refresh Rate: measured in Hz (higher is better)
1Hz - Updates once per second (typical update speed today)
2Hz - Updates twice per second
4Hz - Updates four times per second
5Hz - Updates five times per second

All of these specifications are properties of the GPS chipset and firmware version. GPS products that share the same chipset and firmware will have nearly identical performance. Today, the SirfStarIII and MTK are considered the best, with uBlox catching up. Many MTK chipset based receivers (but not all) can be "hacked" to refresh at 1-5Hz.

The 2005 MS Streets & Trips USB GPS used a SirfStarIIe with a -142dBm tracking sensitivity. The SirfStarIII is significantly better with a tracking sensitivity of -159dBm.

thepunkerguy · 07-14-2007, 01:22 AM

Alright, well the one i have now is the one that came with MS Streets and Maps 2006 and is a SIRF III unit. Its the Pharos GPS-500. The only one i can find on their website is the iGPS-500, which looks identical, minus the MS Logos. Here are the specs on it from the Pharos website http://www.pharosgps.com/support/spec_igps500.htm
My next question is this, comparing this one and the GlobalSat one, the specs are the same, except for the number of all-in-view tracking channels. The Pharos only has 12 where as the GlobalSat has 20. Is this a big deal, a noticeable difference? I don't know how important this number is. Would it be worth me spending the money on for the GlobalSat over the Pharos I have now? The GlobalSat also has WAAS, which i don't think my Pharos does, is that a big deal?
- Mike

techfire · 07-14-2007, 02:03 AM

Are you sure that it is SirfStarIII? SirfStarII was 12-channel and SirfStarIII is a 20-channel receiver. Based upon your long TTFF issues, and the 12-channels, it sounds like you have a SirfStarII or some other GPS chipset in your receiver.

More channels can (but doesn't always) mean a faster TTFF. So, there is an advantage to having more channels, but typically only during acquisition. There are currently 30 GPS satellites in orbit. Some of the newer GPS chipsets support 32 channels, but you typically never have more than 12 satellites in view at any given time. The number of correlators also has a significant effect on TTFF, but again, this is a feature of a GPS chipset. SirfStarIII has 200,000 correlators. This is more than any other chipset on the market.

WAAS is the SBAS (Satellite Based Augmentation System) that is used in the United States (EGNOS in Europe). The Pharos GPS that you link to includes SBAS, so it supports WAAS.

If you are having trouble with long TTFF, you should consider these options:
1.) Relocate the receiver (rear deck or external mount)
2.) Upgrade to a GPS receiver with more correlators and better sensitivity
3.) Run your GPS through a powered USB hub (that's wired to battery) to keep the GPS powered while the vehicle isn't running. This will get you the Warm or Hot TTFF numbers that are advertised by your GPS manufacturer.

nobb · 07-14-2007, 02:20 AM

So if you built a 5volt regulator and connected that to your gps to keep it constantly powered (with the two data pins connected to your computer), would that mean you will always be locked on to satellites? If so, wouldnt that yeild even better results than buying a new gps (and cheaper too because the regulator would only cost <$5 to build).

techfire · 07-14-2007, 02:35 AM

If you can keep the GPS powered on when the car isn't, it should make a significant difference. The acquisition sensitivity is always worse than the tracking sensitivity. So you'll be able to track satellites in places that you couldn't acquire locks on the satellites (such as your garage).

That said, you can pickup a new SirfStarIII GPS for less than $40 and could probably sell your old GPS on craigslist for $20.

thepunkerguy · 07-14-2007, 07:51 PM

Like i said in the post i have before, i have the GPS-500 Pharos unit that came with the MS Streets and Trip 2006 and it even says right on the bottom of the receiver "SIRF III", not II. And here is a link to the specs page http://www.pharosgps.com/support/spec_igps500.htm
Maybe the 12 is just a typo and it supposed to be 20? What do you guys think?
- Mike

nobb · 07-14-2007, 08:12 PM

I also have the GPS-500, and it is indeed a SIRF III. I dont think the 12 is a typo. When I have iGuidance loaded, its always x/12 satellites locked on. So I am guessing 12 satellites is the max.

Maybe try building a 5 volt regulator to keep your unit powered on constantly. I dont know how comfortable you are with soldering and stuff, but you can easily build a regulator based on the lm317 chip for really cheap. If you do build it, remember to post the results. It would definately cost less than buying a completely new unit, and you would probably get better results.

Marvin Hlavac · 07-14-2007, 08:42 PM

If you have a SiRFstarIII based receiver, then getting another SiRFstarIII based receiver will unlikely solve your problem. Perhaps you are using too long USB cable extension? Perhaps your car uses the type of windows which doesn't allow radio waves through? Try, at least for testing purposes placing the GPS receiver outside the car.

By the way, most GPS units which came in the Streets & Trips 2006 w/GPS were the Pharos iGPS-360 based on the older SiRFstarII chipset. However, some of the last shipments of S&T 06 indeed included the new SiRFstarIII chipset based iGPS-500 - which is a bit different than the iGPS-500 currently included with S&T 07. The S&T 07 version is much smaller in size, which makes the actual antenna slightly less sensitive.