Detecting which radio stations people listen to?

[dipchip]

I recently saw an article about a "smart" billboard which detected which radio stations passing cars were tuned to and adjust it mesage for the precieved target group.

Any ideas on how this is done? The coupling between the station and the reciever has to be of a low order, the changes in the prevailing field strength has to be small. Then the distance and fact there is dynamic motion involved?

Any knowledge, insights or ideas?

 

[flatulent]

audience surveying

This is done by detecting the local oscillator radiation from their radios.

The area of audience surveying goes back to at least 1920. Every method imaginable has been proposed. In a home, who is watching is as important as what they are watching. One amusing one for in home use is a chemical detector for the chemicals given off by human bodies. Each person has a different ratio of these chemicals.

 

[E-design]

In the UK they use the same method with detection vans driving by houses and determine which TV station a telly is tuned to. They then check to see if that address registers a valid TV license.

E

 

[sick_man]

in the uk vans? cars traveling about
NO these days they walk about with hand held devices in pairs

like the police

personaly i can have a 2p coin recieve television
so i can show the guy at the door
tell him he needs an apointment and he has the correct address
show him my log and tell him too beet it
so i never pay a licence for something whos radiation cooks you slowly

till bed time

as for your radio detector

it is as was first proposed the local oscillator re radiation from the car antennas

any reciever can be monitored using the second IF and the first

all radios for cars i have ever seen use 10.7 mhz IF for the first stage
and 440 - 450 or 460khz or so for the second

perhaps youl find that as each car comes in range first the local osc at 455 is interigated then the second

but bear in mind you can also tell what freq your listening too by leakage at other freq for instance 100mhz + 10.7 = 110.7 +455khz = 111.155.mhz a nice quiet freq most places