Multi Purpose GPS receiver

[pjpearce]

I am looking to put a portable GPS routing system in my car, and have a separate hand-held device for walking/cycling.



It seems that a Garmin/Magellan unit with NMEA output would be an ideal answer, but I need the speed/sensitivity of a SiRF II receiver for the car.



Does anybody have any idea/experience of what type of hand-held (if any) will fit my requirement.
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pjp

[Dave]

If you're definately looking for a handheld GPS, then you can use this in-car too. If you wanted a Pocket PC or Palm street routing system with re-routing and voice navigation then you can simply connect a Garmin or Magellan up to either a Pocket PC or Palm and get the best of both worlds. Both Garmin/Magellan won't be a problem in-car, but I would suggest going for one that has a Quad Helix antenna as you'll get better signal in-car. Either something like the GPSMap76 or any of the Magellan Meridian range have Quad Helix antennas and you wouldn't notice any difference from say a powered in-car GPS Receiver. The only downside would be that you would need to power the Garmin with batteries. There are several powered cable sets, but one I've tried I had bad experience with the cable melting, so if you wanted to use a handheld GPS in-car, then I'd suggest sticking with batteries.

[pjpearce]

Thanks Dave,



I guess your answer is what I expected, I am only now concerned with the re-acquition time of the hand-held GPS units compared to the dedicated in-car SiRF II receivers (~ 0.1s).



Does anybody know what chipset's are used by the hand-helds manufacterers and their re-acquition times.



I am harping on this subject since I will be spending quite a lot of time in the "Urban Canyon" and I want to be sure the above solution is workable.








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pjp

[Dave]

Although most of the handheld manufacturers won't tell you re-acquisition time, it really won't be much of an issue. I have a Garmin GPSMap76S and coming out from a tunnel will re-acquire from 0 sats to 7 sats within a couple of seconds.



The only issue you'll have is batteries, you'll need to keep recharging them or find a reliable in-car accessory charger for the handheld GPS Receiver.

[pjpearce]

The major issue here, as I see it, is "within a couple of seconds".



If I am driving downtown somewhere, between high buildings, I might possibly get satellite signal(s) at junctions (unless there is one directly overhead), which I would cross in about a second or so, this would imply that a normal hand-held GPS receiver would fail to locate itself at all unless I stopped in the middle of a junction.



The beauty of the SiRF II receiver is that it can re-acquire lock (even on a single satellite signal) in 0.1s - plenty of time when crossing a junction.



So it comes back to, how fast can hand-held GPS receivers re-acquire position lock, and can they lock/ track with only a single satellite signal.



Since Garmin/Magellan etc. do not publish this information, I must conclude that I cannot use a hand-held GPS receiver for car use in city centres.



I would be very interested to know if anybody has successfully used a hand-help GPS receiver, connected to a Pocket PC or Palm in city centres.


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pjp

[DavidW]

Certainly Garmin use their own GPS chipsets and they don't publish a right lot of information about it. I'm not sure about Magellan.



One thought that comes to mind is a Fortuna GPSmart, which uses a SiRF chipset (not sure precisely which one - but it will be a recent one). It appears there's PDA cables available for the cheaper model, or if you have Bluetooth on your Pocket PC you can use the Bluetooth model.





I guess a look in the Fortuna forum will see what people think of them. I know very little other than they exist.







David

[Dave]

pjp, I quite frequently use a Garmin GPSMap76S both walking and driving through city centre's and London and don't have any issue with re-acquisition. 2 Seconds has been my slowest time, on average, it's probably just short of a second.



I use a large combination of CF card GPS Receivers, Bluetooth, in-car GPS mouse, and I'd say certainly the Garmin's with the Quad Helix are on par with all the other's running SiRF I or SiRF II.



The only thing I would recommend against is going for a hanedheld receiver that uses a patch antenna.

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