Plane & Pilot
Tuesday, April 23, 2013

Dual Electronics XGPS170


A new portable passive ADS-B receiver


The reason it didn't detect traffic is a function of how the ADS-B system works. There are two completely different data channels. The first is an enhanced version of the Mode-S transponders already used by the vast majority of airliners, business jets and turboprops, which operate at 1090 MHz.
Devices like this are a bargain for pilots needing in-flight weather data. unlike competing satellite-based systems, ADS-B weather doesn't require a subscription.
For technical reasons, the FAA decided to offer a different data channel for low-altitude general aviation operators—that's the 978 MHz system used by the XGPS170 and other passive devices. A network of ground stations has been installed covering most of the continental U.S. (and parts of Alaska), that offer a rebroadcast function. This system translates between the two data channels, so that aircraft equipped with 978 MHz equipment can see 1090 MHz Mode-S traffic (and vice versa). The ground stations can also relay traffic that is detected by ground-based radar.

Here's the catch: The ground stations only relay traffic on a channel if they're in contact with an ADS-B equipped aircraft on that channel—and then relay traffic within a certain volume around any such aircraft. In other words, to get service you're expected to transmit, as well as receive. The system isn't designed to support passive devices that don't transmit.

In order to get reliable traffic indications on the XGPS170, you'd also need to install a 978 MHz universal access transceiver (UAT). If someone else with a UAT happens to be flying nearby, then you might see some traffic—but the ground station would be relaying traffic based on a volume around that aircraft, not around you. Given these limitations, I can't recommend the XGPS170, or any other passive 978 MHz ADS-B receiver, for traffic awareness.

On the other hand, I'm delighted to recommend the XGPS170 as a completely functional GPS and weather awareness device for pilots who fly within U.S. ADS-B coverage. Devices like this are a bargain for pilots needing in-flight weather data—unlike competing satellite-based systems, ADS-B weather doesn't require a subscription.

Dual's suggested price for the XGPS170 is $799.99. For more information, visit http://gps.dualav.com.



0 Comments

Add Comment