Road Angel UK

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Global Positioning Satellites

A network of satellites that continuously transmit coded information, which makes it possible to precisely identify locations on earth by measuring distance from the satellites.

US department of defense satellites constantly circling the Earth. The satellites transmit very low power radio signals allowing anyone with a GPS receiver to determine their location on Earth, whether on land on sea or in the air.

The first ones where put into orbit in 1978 with a full compliment of 24 being reached in 1994.
Available for civilian use since the 1980s.

The NAVSTAR ( Navigation Satellite Timing And Ranging) system consists of 3 parts.
The satellites, at least 24 satellites (21 active plus 3 spare) in high orbit about 12,000 miles above the Earth, arranged so that 4 are "visible" with a GPS receiver on the earth at any one time. Travelling at 7,000 mph, this allows them to circle the earth every 12 hours. Power is solar energy with a backup battery and they are built to last about 10 years.
Frequency is 1575.42 MHz.
The time it takes the signal to reach the receiver multiplied by the speed of light gives the distance from the satellite. Receive from 3 or 4 satellites and your receiver can calculate it's 3 dimensional position on the Earth.
Ground stations, the ground stations consist of one master control station and 4 monitoring stations. The monitoring stations collect data from the satellites regarding their position and the time they have on board. This information is sent to the master station, corrected and then sent back to the satellites and so keeps the satellites as accurate as possible.
The user, users are anybody who carries a GPS receiver, including the military, boaters, pilots hikers and motorists.

Road Angel checks its position every second and is able to work out accurately the speed of the vehicle.

Road Angel can store up to 50,000 unique locations on it's GPS database..

Road Angel is constantly comparing its position with the stored locations on the database. When the vehicle gets close to a stored location the unit gives an audible alert with a series of beeps and a visual alert with the screen turning red and the distance indicators lighting up.

Road Angel will not give a false alert for speedtraps facing the wrong direction it uses complex heading software so it alarms only in the direction the camera faces.

As with all GPS technology, when Road Angel is first powered it must acquire satellites to know its position. The first start is known as a cold start which can take up to 45 minutes to acquire the minimum three satellites for correct operation, in our experience it has never taken longer than 15 minutes. Thereafter, warm starts (when the unit has been switched off overnight) should take a matter of minutes and hot starts (same day) a few seconds. When the unit has acquired satellites the display will show the vehicle speed, if the vehicle is stationery it will show "000mph".

If after this period of time the unit is still not showing speed, reposition the unit where it will have a better view of the sky. You can check to see how many satellites it has acquired by scrolling through to the 'sat' menu.