Back in the 60's we made traffic loop detectors with a solid state transistor radio tuned to a 24/7 AM station (CFRB 1010) for the Toronto centrally computerized traffic control system. Since this was full AM we were able to ignore the modulation and use the carrier only. Setting a relay to be open when no vehicle was present and the antenna effect with a car or motorcycle was present would close the relay. A little experimentation allowed us to get an all weather setting.
This was done because sensor makers wanted a huge amount of $$ for making one of these. This was thought up by Mario P. Vano, a ham radio man and head tech on the project. He is now in Minneapolis area.
Just google "vehicle loop detector" and all sorts of results/manufacturers should show. Worked with many brands over the years, Sarasota is a big manufacturer. Most are all digital these days, no analog tuned circuits present to best of my knowledge. They are being phased out now to CCTV cameras. The cameras detect a change in the scene, close contact, traffic light changes. This is due to loop failures and having to re-saw cut roadway or dig up old loop if it has failed. Still feel loop detector is superior as it detects vehicles metal mass and not just a change in contrast in the video scene.
loop vehicle detector
Re: loop vehicle detector
