My GPS won't work or works badly in-car (Athermic Windscreen)

Some modern cars are fitted with a special windscreen that cuts down the amount of UV (Ultra Violet) rays that will be transferred through the windscreen which help cut down on glare. These windscreens are called Athermic, or UV Coated and will dampen/reduce GPS signals coming through the windscreen, so if you have an Athermic windscreen, it means you will not receive the same quality of signal as you would do by taking the GPS outside of the car.

How do I know if I have an Athermic Windscreen ?

You can either contact the manufacturer of your vehicle, or talk to the main authorised dealer who may be able to tell you. If you cannot receive a firm yes or no, then another way to check is to purchase a GPS, stand outside, receive a satellite fix and see how many satellites you can see on the GPS Screen. Once you have noted this down, move the GPS inside the car and see if the GPS signal drops by 2-4 sats. If it does immediately then you probably have an Athermic windscreen. We have created a list of cars in the table below that we believe have had athermic windscreens fitted throughout part of their history. Please note that manufacturers don't always use the same windscreens through the life of a car model, so even though a model may be listed below, it does not necessarily mean that the current model that you have may have an athermic windscreen. If you are unsure, try the above test or talk to your car manufacturer/dealership.


BMW 3 Series

Ford Mondeo

Renault Laguna

BMW 5 Series

Fiat Multipla

Renault Clio

BMW 7 Series

Mercedes W220-S Class

Renault Master


Mercedes Vaneo

Renault Kangoo

Citreon Picasso

Peugeot 206

Renault Scenic

Citreon C5

Peugeot 306

Renault Espace

Citreon Xsara

Peugeot 307

Renault Megane

Citreon Xantia

Peugeot 607

Renault Safrane

Ford Territory

Renault Traffic

Vauxhall Zafira


I think I have an Athermic Windscreen, what can I do ?

There's a number of things that you can do to resolve this problem:-

bulletReplace your windscreen or change vehicle (this can be quite costly and is not normally the preferred option)
bulletMove the GPS outside of the vehicle
bulletInstall a patch antenna
bulletInstall a Re-Radiating Antenna

Moving the GPS outside of the vehicle
If you have what is called a GPS Mouse, which is a square antenna with a long cable attached, most of these will have magnetic bases (similar to a patch antenna but usually are a lot larger in size). These can be placed outside the car by running the cable inside the door, and plugging into your PDA or other device.

What is a patch antenna and where can I purchase one ?
A Patch antenna is a small square with a magnetic base. It has a long cable coming out of the square patch antenna and usually has an MCX or MMCX connector on it. If you have an external antenna socket on your GPS, then you could purchase one of these, plug it into your GPS in-car, and have the cable running outside your vehicle and fixed to the top of the car via it's magnetic base. This will now send the signal from outside the car, down the patch antenna cable to your GPS eliminating the problem. When using a patch antenna, the internal antenna on your GPS Receiver will be disabled whilst you take the feed from the external patch antenna.

What is a Re-Radiating Antenna and how do I install one ?
A Re-Radiating Antenna basically is like a patch antenna. You have a small square antenna that fixes via a magnetic base to the top or outside bodywork of the vehicle. A long cable comes out of this, and goes back to a cigarette plug. This plugs into your cigarette lighter socket to give it power as it does something a little bit more than a regular patch antenna. Coming out of the cigarette lighter plug, you also have another cable that will end in a plastic vertical stick (like pen/stylus). This will velcro to the dashboard of the vehicle, and what this will do is pick up the GPS data outside of the car, and passively send it down the cable and re-Radiates the signal internally within the vehicle. This is the subtle difference over a patch antenna, and is much better when you don't have an external patch antenna socket on your GPS Receiver that a patch antenna can be plugged into. These cost a little more up to around the A$150 mark, but are well worth the money and a lot cheaper than having your windscreen replaced.

I have a Bluetooth GPS, can I place it on a back parcel shelf, or near another window ?
Yes you can, some people do this. Remember that Bluetooth data will only be sent over a couple of meters, so it's not ideal for all vehicles, but most cars when they do have an Athermic windscreen, do not have Athermic side or rear windows, so in most cases you could try this first before purchasing a patch antenna or a re-Radiating antenna.

I purchased a Re-Radiating Antenna but it's not helping and it's making the signal worse?
This can happen if you have the Re-Radiating antenna placed too close to the GPS Receiver, or too far away. You may need to experiment to find the ultimate distance. For the RA45, usually it's best to have it around 45cm away from the GPS Receiver. Any further or any closer can effectively swamp the GPS Receiver with too much information (or not enough information) and have an adverse effect.