MODE C decoding

Allan Healy allan.healy121 at
Mon Feb 17 15:46:20 UTC 2014

Hi Pete

Thanks for the reply. Yeah I can see the MODE C transmissions with the rtl_adsb alright but I don’t know how to see the interrogation transmissions from an SSR. Like you said there are many decoders available for MODE S. Hopefully my supervisor will understand the gravitas of the project and will accept MODE S as a suitable solution. Still I will try do some more research. If I am successful I will provide my solution to this forum. Thanks again.


On 17 Feb 2014, at 15:31, Pete Zaitcev <zaitcev at> wrote:

> On Mon, 17 Feb 2014 14:57:44 +0000
> Allan Healy <allan.healy121 at> wrote:
>> My name is Allan an I am currently working on my final year project
>> for college. The idea is to create a radar system that interprets
>> MODE C interrogation signals and replies by aircraft and SSR and
>> with this information determine where these airplanes are in your vicinity.
> I never heard of anyone being able to do that so far. Mode S is easy
> and there's any number of 1090 Extended Squitter receivers and decoders
> out there, but Mode C relies on the illumination by the radar to
> trigger the transmission. Since you cannot know where the radar
> is pointing and when the impulse started (and sometimes not where
> the radar is located), you cannot link Mode C squitter with the particular
> primary target.
> You can receive Mode C with rtl_adsb and have a look at 56-bit packets,
> but they are completely useless for an independent ground station.
> Some people nowadays play with a concept of building a something
> like interferometer from 3 or 4 receivers, but nobody has succeeded
> thus far, as far as I know.
> -- Pete

More information about the osmocom-sdr mailing list