Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site hou4b.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!mhuxj!houxm!vax135!ariel!hou4b!dwl From: dwl@hou4b.UUCP (D Levenson) Newsgroups: net.aviation Subject: Re: IFF/SIF Modes - (nf) Message-ID: <1223@hou4b.UUCP> Date: Thu, 13-Dec-84 08:55:47 EST Article-I.D.: hou4b.1223 Posted: Thu Dec 13 08:55:47 1984 Date-Received: Fri, 14-Dec-84 06:50:25 EST References: <1200006@uokvax.UUCP> Organization: AT&T Information Systems Laboratories, Holmdel, NJ Lines: 19 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