| View previous topic :: View next topic |
| Author |
Message |
neilcharlton
Occasional Visitor
Joined: Jan 06, 2004
Posts: 6
|
 Posted: Fri Nov 05, 2004 1:52 pm Post subject: GPS Cold starts ?? |
 |
|
Hi I recently purchased :
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=4668&item=5730192353&rd=1
from ebay to connect to my laptop with Navigator.
Can anyone tell me more information about GPS cold start and warm up ?
Do these units actually have to be physically warm to work correctly .
As it seems when i start the unit up it can take quite a while for it to find the satellites. Will it help if i warm the unit up in my hands 1st ????
Also the unit sits on my dashboard next to the window . As i use it in central London it regularly looses satellites . Where is the best place to position it ?? Buy a suction cup and place it mid windscreen ?
When these things work its great . When they dont its a nightmare !
Thanks Neil . |
|
| Back to top |
|
 |
icsys
Frequent Visitor
Joined: Feb 20, 2004
Posts: 1154
Location: South Lancashire, UK
|
| Posted: Fri Nov 05, 2004 2:32 pm Post subject: |
|
|
Cold start refers to switching on your receiver for the first time or after a long spell such as a week or so or even you have moved a considerable distance with the receiver switched off then switched it back on again. It has nothing to do with the ambient temperature of the unit so I wouldn't rush out to buy a hot water bottle.
Just make sure that you have a direct line to the sky, and not driving as this will cause a long TTFF.
Warm start simply means the receiver already has the ephemeris data so gets a fix almost immediately (typically 25-40 secs)
TTFF's on most GPS Receivers should be less than 1 minute, usually 50 seconds is an average fix time for most, so if you're experiencing longer fixes, then either you have a heat reflective windscreen, you're commencing your journey before obtaining a fix, or don't have a direct line of sight to the sky. If that's not the case, you probably have a faulty GPS.
I dont recognise it from the picture, do you know the make/model of it?
_________________
Ian.
iPAQ 2210 | Navman 4100 BT Receiver
Navman iCN 635
TomTom GO
Anquet OS mapping
|
|
| Back to top |
|
|
Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
|
| Posted: Fri Nov 05, 2004 3:25 pm Post subject: Re: GPS Cold starts ?? |
|
|
| neilcharlton wrote: | | As i use it in central London it regularly looses satellites . Where is the best place to position it ?? |
Loss of fix is a big problem when surrounded by buildings or heavy tree cover. The ££££ expensive in-car systems often have "dead reckoning" where they monitor the vehicle's speed and direction independently from the GPS receiver to compensate for intermittant loss of signal.
The only thing you can do is make sure that your GPS is situated where it has a good view of the sky. Try putting it on the roof or stick it to the glass of your sunroof (if you have one). Most people just put the receiver on the dashboard and it works fine most of the time.
If you have a heated (some Fords) or heat reflecting windscreen (the ones with a distinctive blueish tinge to them when viewed from outside) then you will have problems using the GPS on the dash and you will probably need an external aerial.
The other thing is that the GPS must "see" a satellite for 30-60 seconds continuously before it can lock on to it and use it. If you are moving and the sats are appearing and disappearing from view then the GPS can't get a first ("cold") fix on them. Once the GPS has a lock on a satellite ("hot" or "warm"), it can reaquire it virtually instantly.
The satellite data goes "cold" after about 6 hours of being switched off and it has to get the 30-60 second continuous view again to lock on. The worst case situation for a GPS is to park in central London for > 6 hours with no signal and then attempt to cold start while surrounded by tall buildings.
Good luck!
_________________
Gone fishing! |
|
| Back to top |
|
|
neilcharlton
Occasional Visitor
Joined: Jan 06, 2004
Posts: 6
|
| Posted: Fri Nov 05, 2004 6:34 pm Post subject: |
|
|
thanks for all the replies. When i drive into a more open area it tends to aquire the sat's easier.
The gps is just a cheap one from Hong Kong , obvioulsy you get what you pay for .
I live on the top floor of some flats in Maida Vale so maybe if i aquire the sat's on the balcony before i leave it might help things a little .
I'll also try sticking the reciever on the roof , it seems to have a magnet on the bottom , unless thats the internal electronics. |
|
| Back to top |
|
|
MrSpock
Occasional Visitor
![]()
Joined: Oct 23, 2004
Posts: 14
Location: Nottingham, United Kingdom
|
| Posted: Sat Nov 06, 2004 10:45 am Post subject: |
|
|
Does that mean then that every time I want to drive off in the morning, when I bring my newly charged GPS and put it onthe dash, I have to wait for a few minutes before I can drive off? Surely so since the unit is undergoing cold start?
Steve |
|
| Back to top |
|
|
Dave
Frequent Visitor
Joined: Sep 10, 2003
Posts: 6460
Location: UK
|
| Posted: Sat Nov 06, 2004 2:38 pm Post subject: |
|
|
Yes, it's best to acquire the satellite lock BEFORE starting your journey. At minimum this will take 30 seconds on a cold fix, most a couple of minutes (on average).
30 seconds is all it takes to download the Ephemeris table from the satellites and to acquire a 4+ satellite fix (3d).
If you start driving before you receive this then you may be passing trees, receiving multi-path errors due to receiving re-bounded signals from buildings and you will then have to wait for the next 30 second transmit start point, and this will add time to acquiring your overall satellite fix.
What I always suggest (and do) is as soon as I get in-car before doing anything else I switch on my Bluetooth GPS Receivers, or put the key in the ignition to power the cabled GPS receivers. That way whilst I'm starting to set up the devices, it's always received a full fix before I start to drive away. |
|
| Back to top |
|
|
Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
|
| Posted: Sat Nov 06, 2004 3:32 pm Post subject: |
|
|
| neilcharlton wrote: | | The gps is just a cheap one from Hong Kong , obvioulsy you get what you pay for. |
Hmm, check and see which chipset it has in it. Most GPS units use the SirfStar II chipset so the the performance of your cheap one from Hong Kong is pretty much the same as a reassuringly expensive one from Britain. 
_________________
Gone fishing! |
|
| Back to top |
|
|
icsys
Frequent Visitor
Joined: Feb 20, 2004
Posts: 1154
Location: South Lancashire, UK
|
| Posted: Sat Nov 06, 2004 6:01 pm Post subject: |
|
|
According to the specs listed on Ebay, it has the SiRF Star II/LP" high performance and low power consumption chipset.
Unfortunately it doesn't list the manufacturer.
_________________
Ian.
iPAQ 2210 | Navman 4100 BT Receiver
Navman iCN 635
TomTom GO
Anquet OS mapping
|
|
| Back to top |
|
|
|
![]() Posted: Today Post subject: Pocket GPS Advertising |
|
|
We see you’re using an ad-blocker. We’re fine with that and won’t stop you visiting the site.
Have you considered making a donation towards website running costs?. Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!
|
|
| Back to top |
|
|
|
Forum FAQ
Search
Usergroups
Profile
Log in for private messages
Log in
