View previous topic :: View next topic |
Author |
Message |
g4ens Occasional Visitor
Joined: Jun 16, 2007 Posts: 13
|
Posted: Wed Jan 14, 2009 5:37 pm Post subject: External antenna for the new TomTom Go 540, Go 740 & Go |
|
|
I can't find any details of the external antenna for the Go 540, Go 740 & Go 940 range.
Can anyone help?
Reg. |
|
Back to top |
|
|
dlpruk Regular Visitor
Joined: Dec 24, 2006 Posts: 88 Location: Nottinghamshire
|
Posted: Wed Jan 14, 2009 6:10 pm Post subject: |
|
|
I'd be surprised if you need an external aerial for a 540 as mine works very happily indoors.
David |
|
Back to top |
|
|
mikealder Pocket GPS Moderator
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
|
Posted: Wed Jan 14, 2009 6:15 pm Post subject: |
|
|
There is no connection available for an external GPS aerial on the x40 range - Mike |
|
Back to top |
|
|
g4ens Occasional Visitor
Joined: Jun 16, 2007 Posts: 13
|
Posted: Wed Jan 14, 2009 6:52 pm Post subject: |
|
|
Thanks Mike.
I find this a surprising omission, having always used an external antenna since 1996 when I bought my first GPSr.
Looks like TomTom are dumbing down their newer products, just like Garmin. My reason for looking elsewhere! |
|
Back to top |
|
|
mikealder Pocket GPS Moderator
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
|
Posted: Wed Jan 14, 2009 6:56 pm Post subject: |
|
|
The newer devices contain receiver chipsets that are better in terms of sensitivity, the older devices used to struggle under Athermic glass needing the external aerials, the newer units simply work - Mike |
|
Back to top |
|
|
g4ens Occasional Visitor
Joined: Jun 16, 2007 Posts: 13
|
Posted: Wed Jan 14, 2009 7:19 pm Post subject: |
|
|
I drive Land Rovers. My Defender has a heated windscreen and the rear of the cab is aluminium. The Luton Top camper body is GRP and aluminium. The only clear area are the two side door windows. It's almost a Faraday Cage!
I'm interested in acurate tracks and not those locked to the unit's roads.
Radio signals travel in straight lines, so an internal antenna would hardly ever 'see' a direct signal.
I also have a pocket data logger that has a high sensitivity chipset. Yes it works inside buildings, but it's accuracy is not as good as older less sensitive receivers. |
|
Back to top |
|
|
MrT Frequent Visitor
Joined: Nov 14, 2003 Posts: 2143 Location: Surrounded by A1, M1 & M25
|
Posted: Wed Jan 14, 2009 8:04 pm Post subject: |
|
|
Heated windows have narrow filaments in them which GPS signal can pass through. I know I have two cars with them and no problems at all. The car also has metal roof as do most except convertables.
The antenna used will have no effect whatsoever on being locked to the units roads. _________________ Drivelux |
|
Back to top |
|
|
Andy_P Pocket GPS Moderator
Joined: Jun 04, 2005 Posts: 19991 Location: West and Southwest London
|
Posted: Thu Jan 15, 2009 12:12 pm Post subject: |
|
|
As Mr T says, modern units have no problem with heated windscreens at all.
There was an issue with heat REFLECTING windscreens (so called "athermic" screens), but most units with the latest SIRF III GPS chipsets seem to cope with those OK too. |
|
Back to top |
|
|
Darren Frequent Visitor
Joined: 11/07/2002 14:36:40 Posts: 23848 Location: Hampshire, UK
|
Posted: Thu Jan 15, 2009 12:17 pm Post subject: |
|
|
g4ens wrote: | I'm interested in acurate tracks and not those locked to the unit's roads. |
Then an x40 is hardly the most suitable device! Lock to road is the default setting and not configurable in common with most road navigation devices.
Quote: | I also have a pocket data logger that has a high sensitivity chipset. Yes it works inside buildings, but it's accuracy is not as good as older less sensitive receivers. |
Not sure what you are comparing here but a modern receiver chipset is at least as accurate in ideal conditions as any older device and in sub optimal conditions it will hold onto a signal where older devices would not. _________________ Darren Griffin |
|
Back to top |
|
|
philpugh Lifetime Member
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
|
Posted: Thu Jan 15, 2009 12:21 pm Post subject: |
|
|
g4ens wrote: | I drive Land Rovers. My Defender has a heated windscreen and the rear of the cab is aluminium. The Luton Top camper body is GRP and aluminium. The only clear area are the two side door windows. It's almost a Faraday Cage!
I'm interested in acurate tracks and not those locked to the unit's roads.
Radio signals travel in straight lines, so an internal antenna would hardly ever 'see' a direct signal.
I also have a pocket data logger that has a high sensitivity chipset. Yes it works inside buildings, but it's accuracy is not as good as older less sensitive receivers. |
Most cars are partial Faraday Cages but most newer (SiRF III and later chipsets) devices will work well enough. At least your roof (GRP) is transparent to most RF waves unlike us car drivers. Cars are pretty good Faraday cages at most commercial FM requencies - hence the need to use external aerials and the vastly improved reception if using an external aerial with the RDS-TMC units. At GPS frequencies (10 * FM) they become much less effective Faraday cages.
I don't know the x40 series but what does it log - actual position or position after lock to road? I have a QSTARZ datalogger and running this on the dash of my VW BORA gives tracks that are rarely off the road on 1:25K OS maps when plotted - more than accurate enough for my use.
My GO720 very nearly always has maximum GPS bars shown (and this is the same when it is in the car and parked up in a 3 sided corrugated-iron barn on the farm) so I'm not particularly concerned about lack of GPS signals on this device. The only time I've noticed it drop a bar so far is in very heavy rain and city centres - both notorious problems for reception of radio at these frequencies. I haven't used it, yet, in the other problem scenario - heavily leafed trees (dry or wet). _________________ Phil |
|
Back to top |
|
|
g4ens Occasional Visitor
Joined: Jun 16, 2007 Posts: 13
|
Posted: Thu Jan 15, 2009 4:29 pm Post subject: |
|
|
Thanks Phil for an interesting reply. I was quite happy 13 years ago with my Garmin 75 plotting me in a field along side a road on my Psion computer. But things improved and now appear to be degrading. My Land Rover cab is all metal except for the two door windows - top and back all metal.
My Garmin 2610 uses an external antenna that is clipped to the cab roof gutter, so partly shielded by the camper body. The bed over cab is GRP and the rest is metal. Depending on the arrangements of the SVs, the camper body and the fact that I am driving in a valley with many trees; the 2610 will still loose signals.
I also have a Qstarz BT1000 that I leave on the bed under the GRP body. I also have it on my belt at times. I find using Google Earth that as I did a sharp 90 deg. turn; the plot continues in a slight curve overshoot. Then slowly returns to the correct plot.
The track from the 2610, when plotted on Memory Map OSGB maps, does not have this overshoot problem. There are a number of plots from Qstarz trackers on the internet and they show poor accuracy walking under suburban trees.
Garmins departure from 'technical' GPSrs (what can I buy to replace my 2610, that works with MapSource on a Tablet PC?) means that I am having a problem finding a suitable replacement. I have no problem with using more that one GPSr. Garmin, Southampton, suggest the Nuvi 5000, but that only uses pre-loaded maps and not MapSource.
I still use my eMap while walking, as it's replacement the Qstarz, does not plot such an accurate track as the old eMap. The Qstarz maybe more sensitive, but it is not as good on accuracy (and not serial O/P)!
I was considering replacing it with a Garmin 76CSx, as I could use the same maps as my 2610. But Garmin have now withdrawn my second licence that I paid for. That would provide the Serial 232 output I need for connecting to my ham radio, like the eMap.
Having for many years used the excellent Palmtop (that's TomTom's owners) software on Psions, which still provides the best experience for moving maps and waypoint & POI management, I'm struggling to find a current replacement.
My ideal setup would be a navigating GPSr to display and tell me where to go, with the Tablet PC showing where I have been and where I want to go. But waypoint/POI management is inferior to Palmtops old software. As well as MM OSGB, I also have an extensive collection of maps for Europe and beyond, in OziExplorer.
The Geosat 5 blu APRS is a possibility as it will connect directly with my ham radios and display other hams on it's screen. It will also automatically navigate to a moving destination (another ham driving his car), but I doubt I would need that much! |
|
Back to top |
|
|
MrT Frequent Visitor
Joined: Nov 14, 2003 Posts: 2143 Location: Surrounded by A1, M1 & M25
|
Posted: Thu Jan 15, 2009 4:58 pm Post subject: |
|
|
TomsToms do not record tracks and are designed for routing over roads from fixed node to node and not free cross country. The GPS data is not externally output or recorded.
As to the overshoot that is probably the sensitivity of the unit and the recording interval. On MM with a GlobalSat BT338 using WAAS I set a 10 second interval and a minimum change distance of 15 meters. As my HDOP and PDOP are normally less than 3 meters that is sufficiently accurate for me. _________________ Drivelux |
|
Back to top |
|
|
g4ens Occasional Visitor
Joined: Jun 16, 2007 Posts: 13
|
Posted: Thu Jan 15, 2009 5:23 pm Post subject: |
|
|
Thanks Mr T.
I was not aware that the current TomToms do not record or output GPS data. The company became well known for deleting features from it's products in it's early years!
However, my 'more than one' GPSr solution would not rule out an x40. The 940 could be ideal as it has maps of 35 countries in Western & Eastern Europe, compared with only 31 in the 740. I could use a re-radiating antenna system.
But the fact that the major feature of the new product is it's use of a built-in SIM card, that will only work in one country, is rather odd. This suggests that there will be a future upgrade or replacement product that would work in most countries that the maps cover. But they have not quite reached that point in development.
Folk that travel throughout Europe use a number of SIM cards, depending on which country they are in for their normal cellphones. |
|
Back to top |
|
|
philpugh Lifetime Member
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
|
Posted: Thu Jan 15, 2009 5:37 pm Post subject: |
|
|
Interesting comment about the BT1000 (the same as I have). The usual track log position is that the straight lines drawn between the log points 'cut' corners but the points themselves are (more or less) on the track. I have my 1000 set to log every 2 secs as I usually use it for slow activities (walking/cycling/sailing). When plotting I try to ignore the lines as they get in the way! I don't think I have ever seen an overshoot as you describe. I do get the occasional "position wander" - but it's usually within the normal error for commercial GPS systems (~15 metres) but there is nothing you can do about that - it's inherent in the way the system works.
It's difficult to explain an "overshoot" as the system doesn't take into account speed and directional change - it just calculates positions. If it's within the 15m then it should be considered a good positional fix. It just goes to show that you can't rely on these systems for precise navigation - you certainly wouldn't want to use them on an autopilot to navigate yourself into a small harbour for example. And who is to say which of two or more systems logging simultaneously is more correct than the other. I often walk with my QSTARZ1000 and Garmin Colorado 300 logging. The tracks are different - but well within the 15mtrs and the OS don't claim any specific accuracy for paths on their maps.
Don't forget the HDOP (Horizontal Dilution of Precision) so often used by manufacturers is a statistical figure and not an absolute error figure.
EDITED Spelling mistake:
Added: You can significantly improve the accuracy by long-term logging at a single position and statistically analysing the data. Other ways include using differential GPS via WAAS/EGNOS or commercially available services. _________________ Phil |
|
Back to top |
|
|
mikealder Pocket GPS Moderator
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
|
Posted: Thu Jan 15, 2009 6:29 pm Post subject: |
|
|
Re-rads were made illegal a couple of years ago in this country so unless you already have one you won't find them for sale, I think there are also restrictions on re-rads in the USA as I have very recently been exploring the purchase of such a system for a building - Mike |
|
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 |
|
|
|