Here is some information regarding the Honeywell RDR-4B that we have installed in our A320s. So far (other than in the sim), I have only seen the windshear icon taxiing to the gate. Other pilots I have talked to, that have seen the icon, have not seen any false warnings.
According to an engineer from Collins, their PWS radar can process doppler returns from extremely low levels of rain. Well below the level required to be depicted as a green return. So it is possible for their system to detect and display windshear without any rain being displayed on the ND. I assume the same is true for the Honeywell system, but I don't have any documentation for this.The more that I learn about the efforts that went into the engineering of these PWS systems, the more respect that I have for them. I hope you find this informative.
The Kid
1. The radar sets the tilt angle for the PWS automatically to locate the center of the beam at 100 meters above the ground at 6 nmiles. If there is excessive ground clutter that interferes with the PWS detection, then the antenna tile might be increased to position the beam as high as 300 meters above the ground at 6 nmiles. These tilt settings provide the optimum detection of the outflows from the windshear. Only the selected tilt from
the control panel is displayed on the ND, not the actual tilt angle for the PWS mode.
2. The displayed tilt never changes between the PWS and other modes; since the PWS tilt is never displayed. We implemented this way to avoid tilt angle changes every other sweep.
3. The R/T is activated at 2300 ft AGL, but it does not start doing PWS immediately. First, it goes through some monitoring checks (BITE). Then, it establishes the parameters for PWS detection. Since, there is no requirement to display any PWS information until aircraft gets down to 1500 ft AGL, the data bus to the EFIS is not turned on until 1500 ft AGL. That is why you would not be seeing any tilt display above 1500 ft, although the radar is turned on at 2300 ft.