Operation,
Screen Layout and Navigation
139187 / Rev. 500
RGS-2000NG TCAS Test Set Operation Manual
1-2-3
September 2021
Subject to Export Control. See Cover Page for details.
Page 199
3.6.13.4
UAT Overview
UAT messages are bursted messa ges that are aligned with UTC time by means of GPS. The basic
modulation is continuous Phase Frequency Shift Keying with a modulation index of 0.6 and a data rate of
1.041667 megabits/second (0.96us bit period) that produces a +/-312.5kHz FSK signal. One UTC second
is broken up into Ground Segmen ts and ADS-B Segments as shown in the following figure.
F i g u r e 1 . 2. 3 - 1 7 2 U T C S e co n d
Each segment is broken up into specific time slots defined for both ground and ADS-B. Each segment is
250us long and the begi nning of the segment is defined as a "Message Start Opportunity".
The Ground Segments and ADS-B Segments share the same modulation type, but differ in size. The
Ground messages 4.274ms in length containing 432 bytes of payload data. The Airborne (ADS-B)
messages are 265 or 420us in length containing 144 or 272 bytes of payload data.
3.6.13.4.1
Airborne Message Format
Air transmissions start at MSO 752.
F i g u r e 1. 2 . 3 - 1 7 3 A D S- B M e s s a g e F o r m a t