The market for inexpensive portable ADS-B receivers that deliver free in-flight data to Apple iPads and other devices is heating up. Boston-based Radenna pioneered this market with the original SkyRadar unit, which communicates wirelessly with the iPad, providing a means to receive free in-flight weather and traffic data from the growing ADS-B ground station network. Sporty’s Pilot Shop is now selling the $799 Stratus portable ADS-B receiver, which runs on battery power, but offers only weather data and not traffic. Stratus works with the ForeFlight Mobile iPad app, while the SkyRadar units provide weather and traffic on SkyRadar’s own iPad app and the Hilton Software WingX Pro app.

The original single-band SkyRadar, now called the SkyRadar S-2, receives ADS-B data on the 978 MHz Universal Access Transceiver (UAT) frequency and sends data to iPads wirelessly via Wi-Fi. More than one iPad/device can use the data at the same time. The S-2 and the new dual-band D-2 require external 12/24-volt power. A newer unit, the L model, has internal Waas GPS and ADS-B antennas, and is more compact than the S and D models. The S and D models require external antennas (a GPS “hockey puck” and an ADS-B antenna), but the L model can be used with or without the external GPS antenna. The L model also requires external power. Prices are $599 for the L, $679 for the S-2 and $799 for the D-2. These prices have dropped considerably from more than $1,000 for the original SkyRadar UAT receiver when it was introduced. SkyRadar receivers also work with the PCAvionics MountainScope, iFly 700 and iFly 720 hardware.

I tested the dual-band Skyradar D-2 recently using an original iPad and both the SkyRadar and WingX apps. The L model was not yet available, and SkyRadar expected to begin shipping that one on May 20.

The SkyRadar D-2 offers the advantage of displaying ADS-B traffic data (TIS-B) via 978 UAT and 1090ES (extended squitter) as well as weather (FIS-B), which means that it receives both the 978 UAT signal and the 1090ES signal from ADS-B ground stations. The single-channel S-2 and L units receive only on 978 UAT.

No traffic data is available unless an aircraft is transmitting an ADS-B out signal (on either 978 UAT or 1090ES), which is required to “wake up” the ADS-B ground station to let it know to transmit traffic information. There are relatively few light aircraft with ADS-B out transceivers, but business aircraft and airliners are increasingly capable of waking up ground stations with 1090ES ADS-B out signals.

At the time I tested the SkyRadar D-2, WingX was not capable of displaying traffic, so I installed the SkyRadar app and was able to see traffic flying in the Los Angeles area, as well as current weather information. The obvious benefit of ADS-B receivers such as the SkyRadar units is that the data is free, courtesy of the FAA (and of course, our tax dollars). And the SkyRadar boxes include a Waas GPS receiver and external antenna, which eliminates the need to use an external GPS to supplement the iPad’s GPS.

The traffic display shows 978 UAT/mode-C traffic in blue, and 1090ES/mode-S traffic in green. A solid traffic arrow is ADS-B and a wireframe arrow is transponder-generated. The arrow shows the direction of the target; the longer the arrow, the faster the target. Relative altitude is also shown. By placing the SkyRadar App’s information circle over the target, you can quickly see the target’s N-number, speed and relative altitude. During the test, I didn’t see any 978 UAT/mode-C traffic, likely because no nearby aircraft equipped with 978 UAT ADS-B out transmitters were sending a signal to wake up the ground station. I could see this traffic on the Garmin G1000 displays of the Cessna 172 that I was flying.

FIS-B weather works only on the 978 UAT frequency, so 1090ES-equipped aircraft won’t be able to receive free weather data. The SkyRadar and Stratus ADS-B units thus offer an inexpensive way to obtain cockpit weather on iPads. Radenna says that the SkyRadar unit will receive weather data at the flight levels, but you might have to tap into a belly-mounted DME antenna. FIS-B weather products include Nexrad, Metars, TAFs, winds and temperatures aloft, airmets, sigmets, notams, pireps and TFRs.

The ADS-B ground station network already covers a lot of U.S. territory, with 385 ground stations in place covering much of coastal Alaska, and most of the coasts and border areas of the Continental U.S., including the Gulf of Mexico. The full ground station network is scheduled for completion next year.