External antenna for the new TomTom Go 540, Go 740 & Go

[g4ens]

I can't find any details of the external antenna for the Go 540, Go 740 & Go 940 range.

Can anyone help?

Reg.

[dlpruk]

I'd be surprised if you need an external aerial for a 540 as mine works very happily indoors.

David

[mikealder]

There is no connection available for an external GPS aerial on the x40 range - Mike

[g4ens]

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!

[mikealder]

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

[g4ens]

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.

[MrT]

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

[Andy_P]

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.

[Darren]

[philpugh]

[g4ens]

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!

[MrT]

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

[g4ens]

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.

[philpugh]

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

[mikealder]

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

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