TCAS and Transponder avionics
I'm interested in designing a TCAS and Transponder system to put on a light
aircraft. could anyone help?
I know that radioamateurs have built some simplified instrument, but would not to give specifications.
thanks in advance.
The specs are located on http://www.rtca.org and see DO-181C for ATCRBS & Mode-S transponders. TCAS uses UF16 and DF16 Mode-S messages to do its job. The transponder frequencies are 1030MHz for interrogations and 1090MHz for replies. It is a difficult job to receive and transmit, and there are lots of rules and regulations to get one certified for aircraft....that is why they are expensive.
Those documents are expensive too! Any other links you may know about that may have free info. I would also like to build a receiver that would plot aircraft positions. There are some hobby ones out there but they are still S1000. I have googled "mode S physical layer" but can't find much.
http://www.kinetic-avionics.co.uk/sbs-1.php
A little bit more history for other people reading this thread. http://en.wikipedia.org/wiki/ATCRBS
Typical commercial transponders use ATCRBS (Mode 3/A and C) and Mode S. Typical military transponders use Mode 4 and newer more-complex Mode 5.
ModeA is the aircraft 4 digit ID.
ModeC is the aircraft altitude. The ground primary radar uses the reflected high-power primary radar time to determine the distance from the ground to the airplane, then using the altitude from the airplane and simple trigonometry, the location in the air is determined. Unfortunately, only the ground radar station knows this information.
ModeS is a longer transmission and reply. Every 0.5 Sec the transponder sends out a DF11 squitter that provides the unique plane number. The DF11 squitter has been around since the beginning of ModeS. A newer DF17/18/19 squitter has evolved since the late 90's that provides 3-dimensional space location. Even if you capture this information, you have to run all the packed-data bits through a long algorithm to convert it into 3D space coordinates.
Typically a transponder waits for an interrogation before it send a reply, except for squitters which are replied at a common rate.
Added after 11 minutes:
There ModeS Squitters and Replies look like this waveform at 1090MHz. The pulses are simple CW and no modulation...the pulses are either there or not there.
I forgot to say the new transponders get the coordinate information sent by the DF17/18/19 squitters from GPS / GLONASS and other sources. This entire new schme is known as "ADS-B" so do some searching on it too. Another term to search is "TDS-B" is some what related but just more information.
Added after 15 minutes:
TCAS is a method for tranaponders on 2 airplanes to communicate with each other, using ModeS UF16 / DF16 messages, to tell each other their relative location and projected flight pathes. If the projected flight path for either plane comes too close, then the transponders will coordinate with each other and the planes avionics flight system to give audial warnings to the flight crew.
Added after 5 minutes:
Another very good source is the Aeroflex/IFR test equipment manuals. There is complete waveforms and other good information. http://www.aeroflex.com/products/man...RF%20and%20IFF