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Satellite navigation systems – questions and answers

How do satellite navigation systems (sat navs) work?

Sat navs use a Global Positioning Satellite (GPS) receiver to calculate their position on the Earth’s surface.

This is combined with a road map to show your position within 10 metres. Sat nav software calculates the ‘best’ route between two points, using known data like average road speeds.

All sat navs give voice instructions, like: “Turn left in 300 yards!” Many systems also show the map of your route ahead on a colour screen.

Some sat navs let you type in your destination as a postcode, which is quicker than fiddling around typing in a whole address.

What can I expect from my sat nav?

Sat navs are best seen as ‘co-pilots’ that give you guidance, but leave you to make the decisions. A sat nav can’t make judgments, and it won’t drive the car.

How should I prepare to use my sat nav?

It’s a good idea to read through the system’s quick start guide. These things will also help:

  • Sit in your car and think where would be a good place to put the sat nav. It needs to be somewhere you can see it easily, but won’t interfere with your driving or paying attention to the road.
  • Most sat navs come with a bracket that attaches to the windscreen with a strong sucker.
  • Position the sat nav as low down as possible so you can still easily see the road, and all your car’s instruments.
  • Tap in all the details you have to help your sat nav work out a route to your destination. The postcode is easiest, but otherwise you’ll need to be able to spell the name of the road, town and county.
  • If the address you want to get to is new, your sat nav probably won’t be able to find it. Most systems only update every six months. So if the address you’re going to has only just been built, maybe think about entering the address of somewhere nearby that it will recognise.

Do I need an aerial for my sat nav?

No. All portable sat navs have antenna built in. They pick up the GPS signal that tells the sat nav where it is.

That said, some ‘hard install’ sat navs, like replacement radio units or Trafficmaster installations, need a separate antenna. But they’re included when you buy them.

Some manufacturers offer extra external antennae. These can improve the performance of your sat nav, particularly in built-up areas. But you don’t have to buy one.

Can sat navs be used in any car?

Generally, yes. We’ve heard of some cases of cars with heated windows not getting great reception. It’s best to try a sat nav in your car before you buy it.

What route options do sat navs give you?

Most sat navs give you a good number of options. Usually you can choose the quickest or shortest route, to go via a town or place of interest – or a route that avoids motorways.

Will I still need an atlas?

Don’t ditch the atlas. It’s always worth sense-checking the route your sat nav’s given you on an atlas. Don’t just rely on the sat nav. It won’t always know where the traffic is likely to get hairy – like on the M6 around Birmingham. And it doesn’t know if you’re travelling in rush hours.

Checking the Highways Agency websites can help you see if there are road works or major snarl-ups before you set off.

Traffic England, Traffic Wales and Traffic Scotland

Should I believe the sat nav’s estimated journey time?

It’s a reasonable guide, but a sat nav assumes you’ll be able to travel at average speeds. So if things slow up, or you stop to stretch your legs, it will take you longer than the sat nav estimate.

Are sat navs distracting to use?

Sat nav lovers say they take the stress out of driving and help you to get where you’re going safely and quickly. Which? has tested and compared a lot of sat navs, and says some are more distracting than others.

Things that keep distraction to a minimum include wide screens, clear and simple prompts and user-friendly features.

Can I take my sat nav on holiday in Europe?

Some sat navs come with European maps installed – and most can be upgraded to include them. If you’ve got European maps, you can just put your sat nav in your hand luggage and use it in a hire car when you get off the plane. Bear in mind that a lot of countries ban the use of speed camera detectors, and can fine you for using them.

Remember that your sat nav won’t necessarily know that some mountain roads close or become impassable in the winter – or that some bridges can be out of action when water levels are up. Make sure you pay attention to road signs as well as the sat nav.

What about traffic information for sat navs?

A few sat nav makers give basic information for free. However, most manufacturers offer it as an extra which you can pay for either with a one-off fee, or a monthly or annual subscription.

If you don’t normally come across traffic jams, this might be an unnecessary expense. Also, if the congestion is something that happens all the time – like on the M25 – the traffic information may not flag it up.

Are speed camera detectors legal to use in the UK?

There are three types of camera detectors:

  • GPS units that tell you where fixed cameras are. These are legal in the UK.
  • Jammers, which use a laser signal to cameras which prevent them from taking a reading. These are illegal.
  • The third type picks up signals from mobile cameras and vans. These are currently legal in the UK, but this may change.

What about sat nav map updates?

If you don’t update your sat nav’s software, it won’t know things like where new roads are, or if one-way systems have been introduced.

Portable sat navs can usually be updated by connecting it to your computer and the internet. You can also buy SD memory cards with the maps already loaded onto them. Most phone-based sat navs can download updates through their GPRS connection. And to update a factory-fitted sat nav, you usually have to buy a data DVD from a franchised car dealer.

Updating can be an expensive business, particularly as new information is released a couple of times a year. A new DVD for a factory-fitted sat nav will set you back at least £150. Portable sat nav updates can cost from £40 – £100.

How do I still drive safely while using my sat nav?

  • Read through the route before you set off.
  • Never try to alter the sat nav settings while you’re driving. If you need to change anything, find a safe place to stop.
  • Make sure you don’t block your view with it.
  • Remember, sat navs do make mistakes. Don’t just follow them blindly. If it doesn’t look like there’s a bridge over the river – or that mountain pass looks dangerously narrow and steep, stop and check the road atlas.

How do I stop my sat nav making my car a target for thieves?

Sat nav thefts are on the up – in 2006, the Metropolitan police said in 50% of thefts from cars thieves took the sat nav and left everything else in place. However, there are a few things you can do to deter thieves:

  • Take portable sat navs and brackets with you when you leave the car.
  • Clean suction pad marks off the window or dashboard.
  • Don’t keep the sat nav in your glove box. In fact, leave the glove box open to show you’ve got nothing worth taking.
  • Don’t record your home address in the sat nav. If thieves get hold of your sat nav, they may decide to burgle your home too – especially if you’re clearly not in it.
  • Identify your sat nav with security markers.
  • Make a note of your sat nav’s make, model and serial number.
  • Think about recording your sat nav’s details on a register like

Is my sat nav covered by my car insurance?

Every insurance policy is different – so check with your insurer to see if you’re covered, and what your excess is.

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