Re: [Discuss-gnuradio] Mode-S/ADS-B and UAT

[Andrew Rich]

I have been doing Mode S with a DSO accessed via the USB port and the video 
out on an SBS-1

Using LINUX to decode the samples.

Set trigger. and download

- Andrew -


----- Original Message ----- 
From: "Eric Cottrell" <address@hidden>
To: <address@hidden>
Sent: Monday, December 06, 2010 11:10 AM
Subject: [Discuss-gnuradio] Mode-S/ADS-B and UAT


Hello,

I was emailed by a few people off list that are interested in the 
Mode-S/ADS-B code.  I am still working on it.

I got the DPD Productions antenna just before Thanksgiving, but it was too 
windy to put up right away.  Sitting on the first floor in the middle of a 
wood frame house, the antenna was picking up aircraft from 40 to 140 miles 
away depending on direction.  I could not see low altitude aircraft to the 
south of the nearest busy airport, which is eight miles south.  44 feet 
above the ground on my roof is a different story and I can see aircraft from 
150 to 210 miles depending on direction.  Although the DPD antenna is higher 
gain, I do not get the same level of interference as the colinear.  The DPD 
antenna is suppose to be a narrow bandwidth antenna.  I tried the wideband 
preamp with the DPD antenna and had the same problem with the noise floor 
rising and decreasing range.

I bought a SBS-1 last week.  It is a commercial Mode-S/ADS-B receiver that 
is smaller than the USRP.  The sensitivity seems slightly better.  It could 
handle the wideband preamp better with just a slight decrease in range.  I 
am currently working on providing a port 30003 compatible output for my 
receiver.  Then I can use Planeplotter and can compare my code to the SBS-1.

My nearby major airport has a ASDE-X system for monitoring aircraft and 
vehicles on the airport surface.  It appears they are installing an ADS-B 
Multilateration system as I get a couple of the sensors.  They use DF18 
(Non-Transponder Extended Squitter) and just send an ID and Multilateration 
status.  Two of them ID as STEST123 with the category of Fixed 
Ground/Tethered Obstacle.  The third recently appeared with an ID of 
PTEST123.  The SBS-1 also picked up the IDs so it can decode at least some 
DF18 formats.

I want to do a UAT receiver and was planning a trip to Philly to look at the 
TIS-B/FIS-B ground segment transmissions.  I got a surprise when I found out 
the New England area has TIS-B/FIS-B services.  Someone did a demo of a 
receive only system.  The TIS-B service only transmits if there is a ADS-B 
aircraft using UAT in the area.  Being able to receive TIS-B would be good 
because it includes non-ADS-B aircraft.  There is also cross-linking of UAT 
and Mode-S so ADS-B aircraft on Mode S ADS-B should show up on UAT.
http://www.youtube.com/watch?v=NmYrUGxRC88

It is an iPhone application using a separate UAT receiver costing $1100.
http://www.skyscope.net/

I looked at the 978 MHz UAT frequency and think I see the signal but it does 
not completely match up with the specifications.  The system uses slightly 
over 1 megabit per second FSK with a over 600K shift.  I see what looks like 
the mark frequency, but instead of the space frequency I get another signal 
at the center frequency (978.0 MHz).  If I use a simple PLL FM detector flow 
graph with a scope sink I do see what looks like a bitstream.  The current 
plan is to get my laptop updated and setup, then go mobile.  I suspect there 
is a transmitter at a nearby airport.

73 Eric

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