Aircraft - ADS-B REceiver, R820T USB RTL-SDR DVB-T Dongle, Propeller or Stamp...

xanatos

Hi folks,

Been a long time since I've been on here... lots happened since then. Among them is that I'm getting my Private Pilot's License. So my hobby project list has grown in that direction as well. I want to build a small ADS-B dedicated, standalone receiver. Not at all worried about it being certified, just want something that'll display the ADS-B messages that I can play with.

Apparently people have been having good luck using the UK USB TV Receiver Dongle, the R820T USB RTL-SDR DVB-T Dongle. But everybody uses it with a PC or a Mac. I want to use it with a Propeller and display it on one of my LCD displays.

Has anyone on here yet built an ADS-B receiver using the R820T USB RTL-SDR DVB-T Dongle - or anything similar - that talks to a Propeller (or even a stamp)? Those of you who remember me know that pretty much all I need is some basic info on interfacing to the unit's USB (not sure if I need an FTDI, or?) and the command set and data format and I can fly with it from there (no pun intended). As far as I understand the output of the R820T USB RTL-SDR DVB-T Dongle will be 8 bit (probably 8/N/1) and should be easy to format/parse.

Thanks for any direction you all may provide.

I hope everybody's been doing well - if any of you have interesting projects going on, etc., I'd be happy to hear from you.

Dave

PS., Ebay for the R820T USB RTL-SDR DVB-T Dongle: http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.TRS0&_nkw=R820T+USB+RTL-SDR+DVB-T+Dongle&_sacat=0

xanatos

Adding these links & info - ADS-B Data Packet Formatting for myself and anyone else who wants to do this:

https://en.wikipedia.org/wiki/Secondary_surveillance_radar#Mode_S

The website http://adsb-decode-guide.readthedocs.org/en/latest/introduction.html contains the following - which is pretty much everything dealing with the format of the data, once it is received correctly... so that's what I need to do now is figure out the hardware interface to the R820T dongle, and the commands to send to it to select the frequency, modulation type, etc., so I can receive the ADS-B data stream.

Here's the lead-in to the readthedocs.org site to give you an idea of the specificity and richness of the depth of info. It appears to have everything you'd need if you want to read ADS-B messages from traffic in your vicinity:



An ADS-B message is 120 bits long:

BIN format:
1000110101001000010000001101011000100000001011001100001101110001110000110010110011100000010101110110000010011000

HEX format:
8D4840D6202CC371C32CE0576098

This table lists the key bits of a message:

Bit from Bit to Abbr. Name
1 5 DF Downlink Format
6 8 CA Message Subtype
9 32 ICAO24 ICAO aircraft address
33 88 DATA Data frame
89 112 PC Parity check

The type of the message can be identified by checking its Downlink Format (DF), bit 1 to 5. For ADS-B message, we need: DF = 17 (in decimal), or 10001 (in binary),

Within the data frame, another import value is the Type Code. it tells what is inside of the data frame, it is located from bit 33 to 37 (5 bits)

Bit from Bit to Abbr. Name
33 37 TC Type Code

ADS-B message types

By looking at the DF and TC we can quickly understand what kind of information is contained in the data frame. The relations are listed as following:

DF TC Content
17 1 to 4 Aircraft identification
17 9 to 18 Aircraft position
17 19 Aircraft velocities

Note that within different type of the messages, the configurations of the bits in data frame are different..........



Much, much more follows on the pages in the site.

Dave

Duane Degn

It's going to be tough interfacing with those USB dongles with a microcontroller.

The FTDI chip allows a Prop or Stamp to communicate with a PC as a USB slave device (with the PC the host). The dongles will require a USB host.
Scanlime wrote some USB host software for the Prop. There are links to her site, OBEX object, and the forum thread near the bottom of this post.

http://forums.parallax.com/discussion/comment/1050128/#Comment_1050128

xanatos wrote: »

As far as I understand the output of the R820T USB RTL-SDR DVB-T Dongle will be 8 bit (probably 8/N/1) and should be easy to format/parse.

That's because you're used to dealing with reasonable serial devices. The "U" in "USB" stands for "Unreasonable". The PC requires a USB device send it information about itself. The exchange is one of the things Micah figured out and it sounds like it's not trivial.

Cool to hear about your pilot's license. Congratulations.

xanatos

Thanks - checking out the links to Scanlime's Host code now...

Dave

xanadu

I don't think the dongle outputs the ADS-B message. The dongle is merely a receiver and everything is controlled via software. You'd still need a computer of sorts, running ADS-B software.

I'm sure there are more expensive receivers with serial output, but the $10 dongles are going to need a fast host.

xanatos

Hmmmm... this seems to be correct - although I'm not too sure that the basic function of some of these ADS-B freeware software downloads might not be replicable in a Propeller. The website I referenced above shows the breakdown of the ADS-B data packet format down to the bit level. It *seems* that as long as I get the RTL dongle tuned to 1090.0 mHz, I should get a data stream. Here's more details about using the RTL dongle with several different Win/Mac/Linux ADS-B readers: http://www.rtl-sdr.com/adsb-aircraft-radar-with-rtl-sdr/

Dave

CRST1

Don't forget if you are looking for tracking on other aircraft on the 1090 band that you will not get dependable info even when you get the stream decoded. The 1090 band will only transmit out when a certified adsb aircraft sends a transmission. So if there are no aircraft in your area transmitting you will not receive anything. Also when a adsb aircraft transmits the reply is formatted to only send information on other aircraft in his area. So you might not receive tracking of aircraft that are near you at all.
I have been looking into this for a while now for the 978 band to receive the weather and the encoding is very complex for that.

Dean

xanatos

Hi Dean,

I'll keep that in mind as I build. I've seen some very impressive results from folks using the RTL SDR setup with some free software like dump1090, etc. Apparently if you know the command set to tune the RTL SDR dongle you can even do it with a terminal server like hyperterm, terminal, etc. But it's a learning project for me and it's really helped me understand ADS-B much better now.

I've thought about creating a "roll your own" all-in-one that includes Mode S, Weather, ADS-B traffic, etc., combine that with Ramsey's no-tune/no-LO Air-Band Receiver kit (which I bought and put together in under and hour - and it's fantastic!) - and create some seriously fun air watching. But I know nothing right now about the formats of the other parts to this - like weather - or what the processing power would need to be to decode & format it all. More fun for later...

Dave

xanadu

Yes, ADS-B requires an ADS-B out signal from a transponder to wake up the ground station. The thing is, by 2020 all aircraft will have ADS-B out, so it's really just a temporary problem. In metro areas you have commercial aircraft taking care of it for you.

You also cannot get ADS-B weather on the ground, so all of your testing will be in the air.

It's too bad those old 1090 mhz satellite receivers that can be modified for 1030 are so hard to find. They had two pins you connect to a comparator, no USB and probably the same price.

Back to the USB part, if you're able to use hyperterm on the dongle that is awesome! Where are you reading about that?

davejames

Hey Dave - long time.

Were you in recovery after exposure to those ultraBetaWhammy waves your last project produced?

Dave