No ADS-B Reception

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AB5R
Posts: 12
Joined: Sat Feb 20, 2016 3:30 am

No ADS-B Reception

Postby AB5R » Wed Mar 23, 2016 4:44 pm

I guess that I am not doing something right or do not fully understanding ADS-B. It is my understanding that the aircraft transmit an ADS-B signal and a satellite rebroadcasts on 1090 or 978 MHz which may be received, decoded and displayed with Virtual Radar software.

My questions are:
1) Is this signal from the satellite AM modulation?
2) Is this a geosync. satellite? Which or where is this satellite?

I cannot receive anything on either 1090 or 978 with a discone antenna, but would I would think that I could see something! There's no since in installing 1090dump if I can't receive the signal. ANY HELP WILL BE APPRECIATED.
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sdrplay
Posts: 582
Joined: Wed Jan 07, 2015 7:58 am

Re: No ADS-B Reception

Postby sdrplay » Wed Mar 23, 2016 5:02 pm

It's a line of sight system and the signal comes from aircraft transponders, so it will depend on where your antenna is located, etc. - the signal is at 1090MHz - I made an 8 stage co-linear antenna - you can find plenty of videos on youtube showing how to make them, it's pretty straight-forward.

Best regards,

SDRplay Support
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DF1KZ
Posts: 19
Joined: Fri Nov 27, 2015 1:37 pm

Re: No ADS-B Reception

Postby DF1KZ » Wed Mar 23, 2016 5:34 pm

Hallo AB5R,

I use the SDRplay together with an ICOM-Discone, 20m aircell7, dump1090 to receive ADS-B signals - it works good.
If the plane is eg 35.000ft high the line of sight is more then 200km if there is nothing in between. Living in a large German city with the discone on the roof abt.12m high I can receive and decode signals from planes up to 100km away.

btw: ADS-B is a transponder-signal transmitted by the planes as an answer on 1090MHz and is (afaik) not received by satellites. ACARS-Signals may be received by satellites and downlinked.

You don't need to care abt. the modulation - this is done by dump1090. Just use "start.bat".

Wolfgang (DF1KZ)
Last edited by DF1KZ on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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SDRplay (RSP1, RSP2 pro) with:
RFsystems DX-10 (14kHz to 50MHz), ICOM Discone AH8000 (10MHz to 2GHz)
12m above ground

AB5R
Posts: 12
Joined: Sat Feb 20, 2016 3:30 am

Re: No ADS-B Reception

Postby AB5R » Wed Mar 23, 2016 5:40 pm

Thank you for reply. Are you saying the signals come DIRECTLY (line of sight) from the aircraft and NOT a satellite? I am not clear on your reply. Line of sight to WHAT? Assume it is AM modulation.

I am about 50 miles south of the DFW airport which is fourth largest airport in world. I would expect to receive something.

Thanks for reply.
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AB5R
Posts: 12
Joined: Sat Feb 20, 2016 3:30 am

Re: No ADS-B Reception

Postby AB5R » Wed Mar 23, 2016 6:17 pm

Thank you Wolfgang. Why would I not need to know the modulation mode? I'm using SDRPlay to receive and SDRConsole software. It has to be set on some mode.

So, you are saying that the ADS-B signal is coming from the plane, not a satellite? My discone is above rooftop; therefore Omni directional.

Beats me why I am not receiving anything. (I just checked continuity on that antenna and it is NOT shorted. Eliminates that, I guess)

Frustrating to say the least. Thanks again for input.
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sdrplay
Posts: 582
Joined: Wed Jan 07, 2015 7:58 am

Re: No ADS-B Reception

Postby sdrplay » Wed Mar 23, 2016 6:32 pm

The modulation used is pulse position modulation (PPM) I believe. It's a digital system and each burst of data contains 112 bits of data.

You would have thought 50 miles from an airport would be good, however from tests that I've done, you'll have more success with planes at a higher altitude. For example, I can "see" planes that are 175 miles away that are at 36000 feet easier than planes that are at a lower altitude but a lot nearer. I also currently have a problem to the East of my location because my antenna is mounted on the West side of my house and not that high up. When I look at the range plots on a map, I have a hole on the East side of my coverage area.

You probably won't be able to decode the signal with SDR software without some sort of plugin or specific application such as the dump1090 software.

Best regards,

SDRplay Support
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AB5R
Posts: 12
Joined: Sat Feb 20, 2016 3:30 am

Re: No ADS-B Reception

Postby AB5R » Wed Mar 23, 2016 6:44 pm

Thanks again. I am starting to get the idea that maybe SDRPlay is not needed? How else would a receive a 1090 MHz signal? I had the impression that SDRPlay with whatever software for it; 1090 dump and Virtual Radar were the ingredients needed. I thought 1090 Dump was written to work with SDRPlay.

What do I know, I am NEW.....DUH.

Regards
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13dka
Posts: 127
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Re: No ADS-B Reception

Postby 13dka » Wed Mar 23, 2016 8:09 pm

I can assure you that reception of 1090 MHz is a lot better with a receiver (such as the RSP1) between the antenna and the computer. :mrgreen: The version of the Dump1090 decoder you can download from the SDRPlay website was specifically recoded to work with the RSP1. Other options are specific ADS-B receivers and RTL-based USB-TV sticks and a decoder that supports them (for example RTL1090 and also Dump1090 for the RTL sticks).

The decoder takes care of tuning, mode setting and everything else on the receiver, that's why you don't have to bother with that at all.

User "SDRPlay" has made an important point as to why being 50 miles away from the airport is not always a good reception point because the planes tend to fly lower around airports. Here's a (sort of) range footprint in relation to plane altitude - first you see the range you get from planes at flight levels >300 (30,000+ ft), then I use the filter slider to make only plane signals from lower altitudes visible (below FL300, 200 and 100).

altitude_vs_range.gif
altitude_vs_range.gif (22.41 KiB) Viewed 2941 times


As the animation indicates, range decreases very much with altitude. In a distance of 50 miles to the airport, planes on the ground are beyond your radio horizon, and approaching planes from all directions except your location will be too, or just slightly above the radio horizon because typical approach glide slopes start at only a few 1000 ft above ground level. So most of the traffic approaching and departing from DFW cannot be seen from your location, only planes at higher altitudes will be "visible". Sometimes high altitude airways are passing above a major airport, sometimes not, so you may or may not be able to see much traffic with different destinations than DFW, and all of it will depend on time of day due to the flight schedules.

Another big point is the antenna. DF1KZ reported that he can receive planes from a distance of 100km / 53 NM (nautical miles) with his discone, which seems to indicate that discones might not be very good for 1090 MHz - even the tiny magnet-mount antennas delivered with the cheap TV dongles will probably do better than that, a tiny quarterwave groundplane or a simple collinear dipole setup for 1090 MHz will be much better and certainly cover the maximum possible range of ~270mi - if no obstructions are in the way.

The latter is another crucial point - at 1090 MHz all sorts of materials will not let anything through, and if you have a hill, a house or a tree in the way, it will cast a shadow if you will and you might not receive anything behind that obstacle. So maybe you just need a little patience to see plane data (from high-altitude overflight) on your Dump1090 screen (to verify the general function of your setup) and improve things from there.
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AB5R
Posts: 12
Joined: Sat Feb 20, 2016 3:30 am

Re: No ADS-B Reception

Postby AB5R » Wed Mar 23, 2016 9:04 pm

Thanks to ALL. I've got it working, sort of. Probably needs tweaking though.

I just did not realize that it would work without the SDRPlay being turned ON.

Regards,
Jerry AB5R
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DF1KZ
Posts: 19
Joined: Fri Nov 27, 2015 1:37 pm

Re: No ADS-B Reception

Postby DF1KZ » Thu Mar 24, 2016 1:24 pm

@13dka
I agree, the discone does not seem to be the best antenna for ADS-B reception. Additionally there are 20m Aircell7 cable in between the discone and the SDRplay but nevertheless I receive a few transponder-signals so I can be sure that dump1090 is working.
Next thing I will do is try to receive weather-balloons on 402MHz to 405Mhz.

Wolfgang (DF1KZ)
Last edited by DF1KZ on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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SDRplay (RSP1, RSP2 pro) with:
RFsystems DX-10 (14kHz to 50MHz), ICOM Discone AH8000 (10MHz to 2GHz)
12m above ground


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