New speed detection?

[Brian Stirling]

I've seen a couple of places that have those electronic sign that tell you how fast you're going that didn't seem to emit radar or lidar. I have a pretty decent radar detector, Escort Passport 8500X50, and most of these signs are detected but a couple get no response from the Escort. Any idea what speed detection method is being used?


Brian

 

[MixMasterTang]

Do those signs in question just display a number as you pass or do you see them actively changing as you increase or decrease your speed? It could be as simple as a measurement of time it took you to get from point a to point b and calculate speed based on that.

 

[LTC8K6]

From another forum:

The speed sign is probably using FM-CW modulation to sense the direction of vehicles in its field of view. FM-CW is allowed for license-free "Part 15" devices by the FCC. FM-CW is not allowed for police radar. Your RD won’t alert because it doesn’t see the frequency.

http://en.wikipedia.org/wiki/Continuous-wave_radar#Modulated_continuous-wave

 

[Brian Stirling]

From another forum:



http://en.wikipedia.org/wiki/Continuous-wave_radar#Modulated_continuous-wave

OK, that makes sense -- radar detectors oerate in the microwave region and many detect lidar as well, but if the emission is outside of the microwave region it aint gonna detect.


Brian

 

[KentState]

The one at work tops out at 45mph.