[Scan-DC] 324.0

[ROCKONYC@flash.net]

Don't forget the military's Mode IV which, if I 
remember correctly, is similar to IFF but a separate 
box in a US military aircraft.  Unlike modes 1,2, and 
3, which are continuously transmitting their codes 
through their transponder, Mode IV requires 
an "interrogation" and a "response" and only US combat 
aircraft and military EW/radar stations (ground or 
airborne [AWACS/E-2/Rivet Joint/EP-3/ES-3, etc]) can 
interrogate mode IV. Responses are simply a yes/no, 
or "friend" or "foe". Mode IV requires certain crypto 
to load and the codes need to be changed daily a Zulu 
hour (GMT).

Rick C.
ex-AWACS guy