emks@uokvax.UUCP (12/10/84)
Is there a difference between IFF/SIF Mode 3 that does or does not report altitude? And what are modes 1 and 2? kurt
levy@trsvax.UUCP (12/11/84)
(from trsvax!levy) Mode 3 can be used with or without altitude encoding. Mode 1, I believe, is left over from an earlier system and only allows a two-digit squawk code. Mode 2 is used by the military.
dwl@hou4b.UUCP (D Levenson) (12/13/84)
Civilian transponders are capable of replying to two types of interrogations, mode A and mode C. The difference between the interrogations is detectable by the spacing of the two pulses which make up the transmission. The transponder answers mode A by sending the code selected by its operator. In answers mode C by sending the pressure-altitude, encoded by a Gray code. Most ATC facilities alternately interrogate modes A and C, thus requesting identity and altitude on alternate polls. Polls occur at a rate of about 100 per second, during the interval that your transponder is illuminated by the major lobe of the ground station's antenna. Military mode 3, I think, corresponds to Civil mode A. I'm not sure what military mode corresponds to Civil mode C, or what the other modes (Civil B, D; Military 1, 2, etc.) are for. -Dave Levenson AT&T-ISL, Holmdel