Radar Identified wrote: When we're safely clear of the apron/ramp area, during taxi we turn the radar on and point the nose (radar antenna is in the nose cone) at a distant object or set of buildings. If there is a rainshower in the area, even better; we tilt up the antenna and see if the rain shows up on our Multi-Function Display (MFD). Only takes a couple of seconds for the radar sweep to pick it up. We then check that the pattern on the MFD "jives" with what we see outside. So more of a practical test than anything.
So it is not an actual calibrated something or other that makes this test independent.
Police radar testing is very similiar (if I'm understanding correctly). After you have done a self test, you basically rely on an object that you can see at a unknown distance (haven't seen a co-pilot get out a tape and measure to a building)
Police radar testing is beyond just a self test. A test also has to be done in regards to our speedometer. Meaning we have to move, activate the radar and see if the patrol speed matches with the speedometer reading, if 2 antennas are being used, this comparison must be done with both antennas. This comfirms the antennas are transmitting and receiving properly, and produces a speed at a known rate.
I had one case where the internal self-check was showing that it was working, even en route, but the antenna had failed (that was one fun afternoon

)... which is why I'm a bit skeptical of internal circuit tests proving that the device is working.
If a self check passed, the officer does the patrol speed comparison and no reading, or intermittent reading, the antenna is not working properly and the unit is taken out of service and sent for repair. Would not be any different with a tuning fork (ding) no reading, antenna not working, unit sent for repair.
Above is merely a suggestion/thought and in no way constitutes legal advice or views of my employer. www.OHTA.ca