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