For anyone confused, "identification friend-or-foe" (IFF) is the military term for what's more generally called "secondary surveillance radar" (SSR) in the civi

For anyone confused, "identification friend-or-foe" (IFF) is the military term for what's more generally called "secondary surveillance radar" (SSR) in the civilian aviation community. This is the backbone of modern air traffic control radar. The Wikipedia article on SSR is a good read if this topic is new to you: https://en.wikipedia.org/wiki/Secondary_surveillance_radar https://en.wikipedia.org/wiki/Secondary_surveillance_radar In the linked video, it looks like the poster is trying to build a small-scale beamformed directional antenna, which is somewhat related to larger larger phased array radar systems. See: https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array > I had very much incorrectly assumed IFF was a coded challenge-response setup It can be, for Mode 4/5 transponders used by the military. The civilian world uses Mode 3 transponders, which are unencrypted. See: https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes https://en.wikipedia.org/wiki/Aviation_transponder_interroga...