Radar Question ATPL

[ibcd]

Hi,
Need help solving this problem.

Q. A radar antenna rotates at 15rpm. It has a pulse width of 2 microseconds, and a beam width of 3 degrees. Two aircraft are flying towards the antenna at the same speed and initial range, but separated laterally by 1nm. At what range from the antenna will the radar first be able to distinguish between the two aircraft?

Possible answer choices:

a) 15nm
b) 20nm
c) 30nm
d) 45nm

Thanks....

[Captain inSensible]

A radar antenna rotates at 15rpm. It has a beam width of 3 degrees. Two aircraft are flying towards the antenna at the same speed and initial range, but separated laterally by 1nm.

Isn't this just the 1 in 60 rule? If the angle is 1Degree, at 60 nm distance the deviation will be 1nm. (just in case you'd forgot:))

So: The radar will be able to differentiate between two targets when they are a beamwidth apart (or greater). The aircraft are seperated 1nm and the beamwidth is 3 degrees, according to the 1:60 rule above that will be when they are nearer than 20nm.

Or am I being too simple?

Capt iS..

[ibcd]

I get it now. Thank you for the quick reply. I was using the 1-60 rule, but incorrectly. :)