Avionics News January 2021 - 59

resources to invest in and build a network similar to the
U.S. system.
For others, a bit of crystal-ball gazing convinced some
to wait on another option, one satellite-based similar
to the position source used by most ADS-B users. That
space-based solution became available in 2019 with the
completion of an Iridium satellite-based system for use
as an ADS-B link, with the vendor a company known as
Aireon.
As the company puts it, " Aireon has deployed the first
global air traffic surveillance system using a space-based
ADS-B network that meets the strict, real-time air traffic
service surveillance requirements for separation services,
anywhere in the world. "
The backbone of Aireon's technology resides on a
constellation of Iridium satellites. Eight Iridium launches
on SpaceX Falcon 9 rockets successfully occurred
between January 2017 and January 2019, each lofting 10
satellites with ADS-B transceivers. The system became
whole when the final 10 satellites were lofted into
orbit on that final SpaceX Falcon 9 rocket in January
2019. That launch completed the 66-satellite Iridium
constellation of Aireon ADS-B transceivers - plus spares
- setting the stage for the next evolution in ADS-B
surveillance: global coverage.
The company Aireon is a joint space-based ADS-B
venture between Iridium Communications, Nav Canada,
the Irish Aviation Authority, Italian air navigation
service provider ENAV, and Naviair - which provides air
navigation services in Denmark, Greenland, and the Faroe
Islands. Nav Canada is the lead air navigation service
provider in the Aireon joint venture.
As Aireon notes on its website, " Iridium hosts Aireon's
specially designed receivers on each Iridium satellite,
providing coverage over 100% of the globe. Iridium's
low-latency, 66 cross-linked low-Earth orbit satellites
make it uniquely suited to meet the technical demands of
global air traffic surveillance and tracking. "
Already, air traffic service authorities around the world
want to use the Aireon network to support their ADS-B
needs. But the Aireon solution raises another equipment
issue for pilots and aircraft owners to resolve: the need for
so-called " diversity " for reliable use of the Aireon satellite
network.
Fortunately, the avionics community was already
working on resolving that need because countries other
than the U.S. require, or will when their ADS-B systems
go live, for users to employ ADS-B Out that works
on 1090 MHz with Extended Squitter and is diversity
compliant.

Diversity: first, it is not a racial thing
Americans hear a lot about diversity, in educational
institutions, in politics, in business and other aspects of
life. " Diversity " in those contexts relates to populating
with people who reflect the diverse mix of American
citizens and residents - Caucasian, African American,
Hispanic, Asian, et cetera.
In the ADS-B world, however, " diversity " relates to an
ADS-B Out source that uses two antennae - one on the belly
of the aircraft, as Mode A/C/S transponders have long used,
the second antenna on the top of the aircraft's fuselage.
The uAvionix tailBeaconX

With only a bottom antenna - the vast majority of
U.S. systems - ADS-B transponders have a clear view
of the Federal Aviation Administration's ground network
of about 800 stations. The bottom antenna, however,
is largely blocked from " seeing " the Aireon ADS-B
transceivers riding on the Iridium satellites.
The solution sounds simple enough: top-mounted
antennae connected to the ADS-B Out transponder.
Unfortunately, adding the top-mounted antenna isn't as
simple as using a splitter to connect both antennae to
the ADS-B Out source. That requires a 1090 MHz ES
ADS-B Out transponder with two transmission sources,
each connected to one of those two antenna - top and
bottom.
Before shop customers and clients question why they
need yet another equipment upgrade, shop managers
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Avionics News January 2021

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