Jake, On Mon, 24 May 2004 16:03:37 +1000, Jake Anderson wrote: > thaught, > perhaps listen for the ground interrogation request? *Very* difficult to do! The interrogation is sent out in a narrow, rotating "beam", so you'd probably have to be airborne and close to the replying aircraft to be able to recveive it at all. Added to which there can be many aircraft and a large number of stations interrogating at any time in a particular area, so knowing which reply is to which interrogation would be something of a lottery. Incidentally a Mode A transponder code is 4 x octal digits, with a possible "Ident" bit, giving a minimum of 22 bits. I'm not sure how you could compress that into 15-ish, as Matt said? Cheers, Howard Winter St.Albans, England > then you will know what the reply is? > > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Matt Redmond > Sent: Monday, May 24, 2004 3:47 PM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [PICBASIC]:TRANSPONDER > > > I assume you mean aircraft transponders? > > You might check SourceForge or similar sites to see if someone is working on > an open-source TCAS-type system. > > Aircraft xpdrs transmit on 1090 MHz. The data is sent as a series of 15 (or > maybe 14 or 16?) pulses 0.45 microseconds wide and 1.45 microseconds apart. > The data is encoded by the presence or absence of specific pulses. Similar > to the way binary data is encoded, but somewhat more convoluted. > > You are going to have some difficulty because mode A and mode C responses > look identical - there is no way to tell them apart. Usually a ground > station will interrogate the xpdr by sending a mode A request then a mode C > request. The xpdr will answer and the ground station will know how to > interpret the response (as a code or as an altitude). If you are going to > listen passively, you won't know which information the xpdr is sending. So > depending on what you are doing (homegrown TCAS?) you might have to > interrogate on 1030 MHz - which is sort of a no-no as it creates clutter on > the frequencies used. > > I have assumed you want to /do something/ with the data. If you only want > to detect the presence of an xpdr and not work with its data, bearing or > distance, then all you need is a receiver tuned to 1090 MHz. > > > > > > From: Fernando Santos > > Date: 2004/05/23 Sun PM 09:44:06 GMT > > To: PICLIST@MITVMA.MIT.EDU > > Subject: [PICBASIC]:TRANSPONDER > > > > Hello > > > > Where can I find a transponder receiver circuit that can detect a > > transponder > > in a distance up to 1m > > > > Thanks in advance > > > > Fernando > > > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body