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Detecting TV receivers

The well known UK RDF system is the TV Detector Vans.  Their main use is psychological warfare.  Their presence in an area is advertised beforehand.  They do a lot of driving around main roads in a town, without actually operating.  The vehicles are plainly marked with large letters.  The word gets around quickly.

A TV Detector Van has a list of all addresses for which a valid TV receiving licence exists.  It drives slowly down all the streets in an area.  Its RDF aerials locate all TV receivers which are turned on.  If an unlicensed TV is found, photographs are automatically taken of the part of the house where the TV is and of the various readings of the RDF equipment.  These photographs are available as evidence in court, to back up statements.

Most people don't think of a radio or TV receiver being able to transmit any signals, but they do.  So do many other electronic devices.  UK and European laws specify maximum signal strength limits for devices which aren't intended to transmit.  Such transmissions don't travel far, but are often detectable in adjacent buildings or outside the buildings.

Animal tracking

There are rules on unmanned transmitters using the amateur radio bands.  On other bands, RDF is used to track the location and movements of seals, sharks (not many in the UK), crocodiles (not many in the UK.  Sharks ate them all), whales, falcons and many other animals large enough to carry a small beacon transmitter with a battery providing a limited transmitter life.

Aircraft tracking

Those who experiment with "model" rockets or radio controlled aircraft may fit them with a beacon transmitter so that if they go out of visual range, they can be located.

Large aircraft are fitted with a black box (often coloured bright orange) flight recorder.  It also contains a beacon transmitter which is activated if the the aircraft crashes.  RDF techniques are used to locate it.

With aviation radio, many airports are fitted with an RDF station.  The instant that a radio signal is received at that RDF building, even before a word is spoken, the RDF station sends a data transmission down a BT private circuit to a central point giving the frequency, time and bearing of the received signal.  The computer at the central point combines all of the information received from several or many RDF stations and logs the location of the aircraft at that time.  The information is available to any air traffic controller who requires it.  Radar systems have dead spots and limited range, so the instant RDF facility supplements radar.

Vehicle tracking

A stolen car may activate a beacon transmitter fitted inside the car in a secret location and without an obvious aerial.  Ferry ports often contain beacon receivers to indicate if a stolen car is being taken out of the UK.  Police forces usually have a few cars fitted with an RDF system to locate stolen cars.

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Page updated on 09 January 2017

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