Hi,
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. The device I am using to receive these transmissions is a DVB-T dongle. I will have to create an algorithm that will use the ping of the above transmissions which I am aware of. My problem is that I am having difficulty understanding how I will decode the signal to read the altitude and differentiate between other aircraft transmitting on the 1090MHz frequency. Could anyone in this forum point me in some direction as to how to learn this? Also apologies if I am unclear.
Regards Allan
On Mon, 17 Feb 2014 14:57:44 +0000 Allan Healy allan.healy121@gmail.com 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
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.
Allan
On 17 Feb 2014, at 15:31, Pete Zaitcev zaitcev@kotori.zaitcev.us wrote:
On Mon, 17 Feb 2014 14:57:44 +0000 Allan Healy allan.healy121@gmail.com 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
Hi ,
just one comment : the interrogation is periodic and stable.. the request is transmitted by a rotating antenna turning at constant speed. If you can get the direct path to the interrogation system, you may estimate the round-trip time and then when the interrogation pulse is sent
sylvain
2014-02-17 16:46 GMT+01:00 Allan Healy allan.healy121@gmail.com:
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.
Allan
On 17 Feb 2014, at 15:31, Pete Zaitcev zaitcev@kotori.zaitcev.us wrote:
On Mon, 17 Feb 2014 14:57:44 +0000 Allan Healy allan.healy121@gmail.com 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
Hi,
as far as I know interrogation requests are send on 1030MHz with a higher bandwidth and a different modulation scheme.
Stefan
Am 17.02.2014 17:11, schrieb Sylvain AZARIAN:
Hi ,
just one comment : the interrogation is periodic and stable.. the request is transmitted by a rotating antenna turning at constant speed. If you can get the direct path to the interrogation system, you may estimate the round-trip time and then when the interrogation pulse is sent
sylvain
Yes, that's true.. but this does not avoid the round-trip measurement...
2014-02-17 17:22 GMT+01:00 Stefan Sydow st@metafly.info:
Hi,
as far as I know interrogation requests are send on 1030MHz with a higher bandwidth and a different modulation scheme.
Stefan
Am 17.02.2014 17:11, schrieb Sylvain AZARIAN:
Hi ,
just one comment : the interrogation is periodic and stable.. the request is transmitted by a rotating antenna turning at constant speed. If you
can
get the direct path to the interrogation system, you may estimate the round-trip time and then when the interrogation pulse is sent
sylvain
Yeah that’s true. I am thinking if I could get the Automatic Gain Control of the transmission from the plane I might be able to give a really rough guesstimate where the plane is in a 2D axis. On 17 Feb 2014, at 16:22, Stefan Sydow st@metafly.info wrote:
Hi,
as far as I know interrogation requests are send on 1030MHz with a higher bandwidth and a different modulation scheme.
Stefan
Am 17.02.2014 17:11, schrieb Sylvain AZARIAN:
Hi ,
just one comment : the interrogation is periodic and stable.. the request is transmitted by a rotating antenna turning at constant speed. If you can get the direct path to the interrogation system, you may estimate the round-trip time and then when the interrogation pulse is sent
sylvain
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Allan Healy -
Pete Zaitcev -
Stefan Sydow -
Sylvain AZARIAN