Raytheon’s ADS-B unit cuts down on

 - February 5, 2007, 5:46 AM

Raytheon Systems Limited (RSL) has unveiled a new automatic dependent surveillance-broadcast (ADS-B) receiver that uses a 16 MHz or better sampling rate, a new algorithm and enhanced error correction to decode 1,090-MHz extended squitter transmissions correctly even in the presence of extreme frequency congestion.

The 1,090-MHz frequency is already crowded with transponder replies to secondary surveillance radar (SSR) interrogations, TCAS squitters, TACAN and DME interrogator transmissions and out-of-band interference from primary radars, DMEs and other emitters, resulting in the phenomenon of false replies unsynchronized in time, otherwise known as fruit.

At last month’s ATC Maastricht show Mike Speed, RSL’s director of ATM systems, said mode-S SSR already provides “selective addressing,” unique addressing to overcome the shortage of Mode 3/A codes, identity retention in stacks and height read-outs in increments of 25 feet, while reducing fruit, enhancing surveillance and reducing R/T workload.

ADS-B improves that by adding improved surveillance accuracy with higher frequency at a lower cost, because the information is transmitted every second rather than five times per minute since the accuracy of the target position does not degrade with distance. Given a suitable cockpit display, it also holds out the possibility of the controller delegating to the pilot responsibility for maintaining separation.

The company has demonstrated the receiver in diverse operational environments over the last year, including the FAA Technical Center in Atlantic City, N.J., which Speed said had described its performance as “miraculous.”

In Mongolia, where it showed its potential to fill gaps in current surveillance or provide coverage where none existed before, the local civil aviation authority asked to keep the equipment on “indefinite test.”

At the Shannon oceanic control center in Ireland it demonstrated the ability to track aircraft 263 nm out over the Atlantic, the sort of performance that might enable the reduction of lateral separation from 60 nm to 10 nm much farther from land than is currently the case.

At the German mode-S experimental center in Gotzenheim, near the high-traffic environment of Frankfurt, it demonstrated a better than 98.8 percent probability of detection.

Meanwhile, at RSL’s Harlow, UK, base–inside the emission-rich London terminal maneuvering area (TMA) and just 12 nm from London Stansted Airport–signals received by a bidirectional antenna on the roof of the office building enabled the new ADS-B receiver to output tracks of aircraft up to 260 nm away. They also revealed that the proportion of aircraft squittering in the TMA “is going up every day” and has increased from 10 percent to 20 percent in the last six months, Speed added.