Hello,
I recently got the WBX daughterboard and updated GNURadio after a year
or two of hiatus. I really like the WBX so far, and have some ideas for
receivers, like an ACARS decoder that decodes multiple frequencies
simultaneously, or a trunked radio decoder that can decode the control
channel and one or two voice frequencies. A suggestion would be a WBR
daughter board that is receive only.
I updated my Mode S / ADS-B code to work with the latest version of
GNURadio and the USRP2. The project now builds outside the GNURadio
project. The USRP2 allows me to have a 10M sample rate receiver. I
have to go back and update the USRP1 version.
I like the updated scope sink. It is easier to use and I was able to
find some bugs, including a few stupid bugs, in my code. It was
interesting using the scope with various antenna and wideband preamp
combinations. The preamp with a 1/4 wave antenna worked good. A
colinear decreased range because of a raised noise floor and increased
interference. I moved the colinear to my roof without the preamp and
get a maximum range from 120 to 210 miles depending on direction. I had
it up 25 feet off the roof until a rainstorm and wind bent the bottom
mast section and now it is 15 feet off the roof. This cut down the
range a little. I have a DPD Productions 1090 MHz antenna on order that
should really fill out the range.
My code implements most of the RTCA recommendations in Appendix I of
DO-260B. I thought I had a good receiver, but as I fix bugs in my code
the receiver performance is improving.
http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/nextgen/research_tech_dev/eng_dev_serv/adsb/wg3/Meetings31/media/pdf/1090-WP31-04.pdf
I only know some basic python so I have external C++ programs that
decode the log files rather than doing the decoder in Python. It is an
advantage when I spot a decoding error. I fix it and run the same log
file through the decoder. I am looking at implementing a socket
interface so my code will work with Planeplotter and other programs.
I want to try using a matched filter for preamble detection and a method
that packages the raw samples in a structure when it detects a preamble.
The following blocks work on this structure instead of a stream.
There are now several hardware platforms for decoding Mode S and ADS-B,
mostly from Europe. The SBS-1 implements a complete receiver/decoder
using a FPGA and possibly a soft microprocessor. The RadarBox sends the
raw bits over the USB and decoding is done on the PC. These are the
major players. I was surprised to see at least three other devices.
http://www.radargadgets.com/
This seems like such a niche market and yet there are at least five
hardware solutions and two GNURadio solutions, including mine. I would
like to compare my code with a couple of other receivers to see how good
it is.
73 Eric