"Tony" wrote in message
roups.com...
Can anyone offer specific info as to the frequencies most commonly used
for a/c searches (non cooperative aircraft, ie xponder off)?

Any radar designed for this can track an airplane with or without the
transponder. It has nothing to do with the frequency.

The various stealth aircraft are even vulnerable to certain radar
frequencies. This type of radar is not very common though.
So even an airplane designed to be invisible to radar can be
tracked with the proper equipment.