The Radar Detector Source

Posts Tagged ‘antennas’

I was traveling along Interstate 5 today between LA and the Bay Area today and was using my new Cobra XRS 9970G. Throughout the trip, the radar detector kept going off with X, Ka, and K alarms. When they went off I couldn’t help but wonder, "Where are these signals coming from?" I looked around and didn’t see any sources for what my radar detector was picking up. (One possible thought I had was maybe they’re coming from the really tall cell phone towers that have the half-ball shaped antennas?) Other than the occasional highway patrol officers and and their vehicles, where are these alarm signals coming from? Or are they mostly false alarms?

A police cruiser sets up a novel radar speed trap, consisting of two transmitting antennas at the edge of a main north-south road. One antenna is 2.0 m [W] of the other. The antennas, essentially point sources of continuous radio waves, are fed from a common transmitter with a frequency of 3.0 x 10^9 Hz. The trap is set for cars travelling south. A motorist drives a car equipped with a radar detector along a east-west road that cross the main road at a level instersection 1.0 x 10^2 m [N] of the radar trap. The motorist hears a series of beeps upon driving west through the intersection. The time interval between successive quiet spots is 0.20s as the car crosses the main road. How fast is the car moving?