FlightAware Discussions

978 Mhz UAT in the US

I’m a little confused on what information is on 978 Mhz in the US. Will general aviation broadcast ADS-B on 978 Mhz? Also I was wondering if is it possible to decode TIS-B traffic to plot like we are doing on 1090? Thanks for the information.

Some GA aircraft will broadcast on 978 MHz, but most are choosing to equip using 1090 MHz hardware. At this time we are not attempting to decode traffic on the 978 MHz frequency, but we are looking into options for simultaneously decoding both frequencies.

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How do you know “most are choosing to equip using 1090 MHz hardware” ?

Unless those GA airplanes already have a mode-s transponder, it is often cheaper for them to go the UAT route.
I’m not sure we have statistics on the 1090 vs 978 choice for GA, you’d probably have to ask a bunch of
different avionics shops to get an answer.

By shipping these cheap ADS-B 1090mhz only receivers everywhere you are discounting all the GA traffic you
will miss by not shipping a dual mode receiver.

This article has some interesting details about ADS-B deployments in the US.
faa.gov/nextgen/media/AEA%20 … lation.pdf

In particular, they say that as of May 2014 about two-thirds of installations are 1090ES and about one-third is UAT (978 MHz). You can assume that larger aircraft that ever need to operate at higher altitudes or fly outside of the US airspace are choosing to equip with 1090, though that doesn’t mean exclusively large aircraft are on the 1090 frequency. Unfortunately, the lower operating altitudes of UAT aircraft will also mean that the transmission range will be shorter since ground obstructions will be more likely to interfere with line-of-sight reception, which means there will probably be a lot more coverage gaps with the same number of receivers.

Although one of the original FAA intentions of the UAT frequency was to minimize installation costs (and frequency congestion), that is turning out to not usually the case since the final FAA ruling was that standard transponders would still be required. For UAT installations, aircraft need to have an additional hardware box that transmits on a separate frequency and synchronizes with the standard transponder so that they are both squawking the same code, which means two pieces of hardware that can fail. For the same cost or less (a low as $2500), you can just replace your current transponder with a TT31/KT74/GTX330ES assuming you already have a compatible WAAS IFR GPS, which will output on 1090 and eliminates the weight, power, buttons, and failure conditions of an extra box. That also has the benefit of taking an old Mode C transponder offline and replacing it with Mode S, which is more bandwidth efficient on the 1090 frequency too.

The majority of the FlightFeeder receivers that we have been shipping have been to locations outside of the US, where 1090 MHz is the only frequency option so being dual-frequency capable is not a factor there. We are actually evaluating ways to support dual frequencies for US receivers economically in a future hardware revision of the FlightFeeder, but we don’t have anything decided or finalized yet.

Does anyone know if those RTL/SDR dongles can support 978?

I’ve been able to tune mine to 978, but have not detected any packets. I’m using code from here: github.com/zaitcev/ruat

Are you using “dump1090” tuned to 978?

No that won’t work because the data formats are different. I posted a link to what I’m using in my previous post.
I had to download and compile it.

The majority of the FlightFeeder receivers that we have been shipping have been to locations outside of the US, where 1090 MHz is the only frequency option so being dual-frequency capable is not a factor there. We are actually evaluating ways to support dual frequencies for US receivers economically in a future hardware revision of the FlightFeeder, but we don’t have anything decided or finalized yet.

I’d be interested to get 978 data on my PiAware box in Maine and report what it sees to FlightAware, hope you will support the software for it.
Would be cool if the NooElec NESDR Mini USB RTL-SDR & ADS-B Receiver Set I bought per the parts list at http://flightaware.com/adsb/piaware/build could support it.
I’d be willing to add another USB receiver to the Raspberry if needed.
Would be great if it could work with the high gain antenna http://www.dpdproductions.com/page_vhf_air.html#adsbout I just ordered.

In Europe some people are equipping small aircraft with flarm equipment - see flarm.com/

This is really intended as a glider anti collision “Flight-Alarm” system but is much lower cost than ADS-B and does provide a location transmission method for aircraft that don’t fall under the ADS-B regulations.

I too am interested in adding UAT a Decode, as there is a FAA ADS-B ground transmitter 2 miles away from my home.

I elected to install 1090ES in both my Gyroplane and My Mooney as I am only required to have one box, instead of two with UAT. Since the FAA still requires the mode-C.

I do have portable Recievers for fis-B and Tis-b

Can you help set this up? As a GA person I’d love to see what 978 traffic is out there. I am an airplane person, not a computer person, and if someone can give some guidance on tuning to 978 I’d love to give it a go.

I have a Garmin GDL-88 installed in my Mooney, have to look to see if it is transmitting on 1090 or 978. Hmmm.

I believe the GDL88 is 978 output only. Your old transponder will still be outputting on 1090, but presumably only legacy mode C or whatever level of output it supports.

That is correct, as I have a Garmin GTX-327 transponder, which is Mode3C only. To put out on 1090 I would have to replace that with a GTX-330ES, which runs about $3700 plus installation cost less resale on the GTX-327, which is probably something like $1100 give or take. Call it $3000 net cost, or thereabouts. Ouch.

I think your assumption that GA is equipping with 1090 is incorrect, unless your definition of GA is “biz jets that fly above 18000 all the time”. Light GA – and there is a lot of light GA – is mainly below 10,000 (at least here on the USA East Coast) and is largely choosing 978 / UAT because it’s a) available and b) cheaper. I wanted the clean integration of ADSB and a certified installation, so I went the full Garmin route when I installed the GTN-650 / GDL-88 / GTX-327 package in my plane.

I will say that having onboard traffic and TIS-B weather has improved my general likelihood of seeing other nearby aircraft traffic when I am flying. The legacy Mode S based traffic availability is becoming more and more rare – I have a GTX-330 (not ES) with GNS-430’s in a Cirrus I fly, and I don’t see nearly the same volume of traffic, and I get “not available” quite often. The TIS-B availability with the GDL-88 has been quite good, ADSB general coverage is getting pretty complete these days.

Just my experience…

– Don

I have recently been experimenting with Mutability’s dump978 (https://github.com/mutability/dump978) using a second RTL dongle on my RPi Model 1 B+ with good success. If you use two dongles, be sure to keep them well separated or shielded to minimize cross-interference.

I generally only see activity during the daytime hours, when most of the GA traffic is up in the air, and also from smaller commercial traffic whenever 1090 gets crowded.


It is interesting that most of the repair facilities I’ve asked are pushing the 978 Mhz hardware for GA. Reasoning seems similar to what is on the FreeFlight Systems website:

**1090ES or 978 UAT?

Aircraft that fly below FL180 can fulfill ADS-B Out requirements with either a 1090ES or 978 UAT datalink radio.
However, a 978 UAT is highly recommended because:

It uses efficient, reliable, low-power, high-integrity digital data transmissions vs. 70-year-old radar-based technology
It only requires a simple retrofit installation for most aircraft.
The 978 UAT paired with an approved ADS-B position source works with existing Mode A and C transponders. The 1090ES option requires replacement or modification of an existing transponder.
The 978 MHz frequency has ample capacity for increased airspace use and for aviation data services while the 1090 MHz frequency is already congested and lacks capacity for growth.**

Certainly this is a US General Aviation issue only.

UATs are MUCH better at data transfer than 1090ES, and for aircraft pilots who want airborne weather and other useful information are definitely the way to go. Airliners went with 1090 mode S transponders because it was needed to support their mandatory TCAS anti-collision systems. General aviation pilots are not required to carry TCAS, hence don’t care much about mode S, and will not be required to have ADS-B Out capability at all until 2020. That being the case, they haven’t been stampeding to spend the money needed to upgrade to ADS-B - there’s really no reason to do that yet. However, as the deadline approaches, more and more will be appearing.

1090 does have some advantages. Equipping any turbocharged GA plane with 978 is silly, because you are now limiting yourself to below FL180. Even some normally aspirated planes can go above FL180. Secondly, you now have to maintain 2 boxes - a 978 transmitter, and a Mode C transponder. If either of them fails (after 2020), you’re grounded until you can get it fixed.

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I was doing some 978 testing last night and saw a flight at 27000 feet. He was broadcasting on 978 AND 1090 at the same time.


Tail number and ICAO edited out:
MDB Type: 1
Address: XXXXXX (ICAO address via ADS-B)
NIC: 9
Latitude: +39.8536
Longitude: -83.4756
Altitude: 27075 ft (barometric)
N/S velocity: 213 kt
E/W velocity: 391 kt
Track: 61
Speed: 445 kt
Vertical rate: -256 ft/min (from barometric altitude)
UTC coupling: yes
TIS-B site ID: 0
Emitter category: Medium Wake 7000-34000kg
Callsign: XXXXX
Emergency status: No emergency
UAT version: 2
SIL: 3
Transmit MSO: 24
NACp: 10
NACv: 2
NICbaro: 1
Capabilities: CDTI ACAS
Active modes:
Target track type: true heading
Sec. altitude: 27175 ft (geometric)