[falcolas]

> Does an amateur license allow you to operate a RADAR system?

Yes, conditionally. RADAR does not fall under the "specifically prohibited" rule for communications, but it's also not explicitly listed as "specifically authorized" either. Likely up to the discretion of whatever FCC official you asked.

http://wireless.fcc.gov/services/index.htm?job=about_1&id=am...

> the ability to detect and avoid [interference with other] signals.

This is a requirement for all amateur radio transmissions. However, so long as you take reasonable precautions (and react to any reports of issues), you can do it.

In my (unprofessional) reading of the phrase "You determine for yourself whether your communications should be transmitted on amateur service frequencies", a reasonably powered experimental radar system which doesn't interfere with other services would be OK.