The TAS units have to interrogate Mode S. It is spelled out in the TSO
I wonder what they use it for?
I believe the Mode C pressure altitude is duplicated in the Mode S data but do they use it? If so, that would be nice because setting e.g. a GTX330 to Mode A (which I suggest is done often deliberately) might still radiate the pressure altitude on Mode S, no?
Peter wrote:
e.g. a GTX330 to Mode A (which I suggest is done often deliberately) might still radiate the pressure altitude on Mode S, no?
I don’t think so. The only operational reason not to squawk mode C would be to avoid confusing ATC ( or TAS boxes) if the reported altitude was incorrect. But that would affect mode S altitude as well.
I am planning to buy tomorrow the TRX-1500A that is advertised that when connected to a compatible transponder such as Garrecht VT-2000, will enable ADS-B out.
Does anyone know if the GPS source of the TRX-1500A sent to the transponder is WAAS (SIL-3) and will result in my aircraft being shown on regular TAS/TCAS equipped planes?
Currently the GPS source of my transponder is a Garmin GNS530 (non WAAS) and everybody seems to ignore my ADS-B out signal, even FlightRadar24 (most of the time).
The information on the manufacturer’s website it’s not clear (must be automatically translated from German).
Thank you!
Sounds fishy to me.
It is easy to make an ADS-B IN + FLARM IN box, which receives everything from SIL=0 to SIL=3, and displays the traffic on some tablet device.
The challenge is to make it so it can display on panel mounted avionics. For a start, supposedly, displaying anything below SIL=3 on certified avionics is illegal.
The Garmin traffic protocol (the one which runs over RS232) is confidential. It can probably be reverse engineered… depending on whether they have some strong crypto in there.
I am not sure if this was discussed here previously but I think the ARINC429 version is better defined and probably easier to reverse engineer. If they have crypto in there, it could be hard or impossible but fundamentally a unidirectional data link can only run with a fixed key and the key must be in the firmware of the transmitting device… So this could open up the data display on panel mounted avionics – even though the installation is likely “technically illegal” unless there is an STC covering the interconnection. In practice most people would connect it instantly without saying anything. Look at the years long wait for the Avidyne TAS6xx ADS-B IN, and there are questions (which nobody can answer) as to whether ADS-B-only traffic will display on which display devices. For example I have been told that my two Sandel SN3500s will not display any ADS-B targets, ever, and nobody knows about the KMD550 MFD. This is nuts, since the data stream could have been kept the same as before.
A box like this, if it works, is an opportunity to deliver a real working solution.
Back in January 2014, exactly a year before this thread started I read an article on how ADS-B works. Today when going through all my old notes in search of information about alternates I found my notes about ADS -B and wondered how much had really changed over the last 4 years.
The three principal systems at the time were,
1090 MHz ES (extended squitter). It worked with a Mode S transponder.It was the system most used by airlines. GA mode s transponders at the time were not totally compatible. They needed upgrading for ADSB. On the Garmin GTX 330 it cost around 1500 euros. However at the time Europe had not committed to investing in the gound stations necessary to send the information to the aircraft so that it could be displayed on a screen. And other information like the weather being sent by the same system was not even being discussed. I’m not sure it was even planned in the USA on this system at the time.
- UAT(Universal Access Transceivers) which worked on a band of frequencies around 978 MHz. They transmitted as blind calls aimed at no one in particular. The FAA ruled that to receive information, aircraft carrying such equipment should emit their identity, their heading, their speed and their altitude. As in the case of with mode S extended squitter, the emitter needs to be linked to a GPS WAAS, EGNOS or Glonas. One receives information on other traffic from ground stations. In the USA it was also planned to send other info, like the weather on this system. I don’t know if European authorities considered this system at all.
VDL4
To continue, finger trouble.
The third system being looked at was call VDL4 (VHF data link 4) It transmitted the same information as 1090 ES and UAT but used VHF bands between 108MHz and 136 MHz. This system was being heavily pushed by the Swedish CAA. It presented advantages over the other 2 systems but the lack of 25kHz frequencies and the move to 8.33MHz put a brake on its development.
They are just my notes at the time, but I’d be interested to know how modern equipment and regulations have developed or not.
Just received an answer from the producer:
the TRX-1500A GPS signal is Source Integrity level 0 (SIL=0)
So it won’t show on any certified TAS/TCAS equipment. I can leave the transponder connected to the existing GNS530, as it makes no difference.
I wish a cheaper, single function GPS WAAS receiver that can forward signal to the transponder would be available, so you don’t have to spend a fortune on a GNS530W…
Has Europe ever intended to send anything up to an airborne aircraft (weather or traffic) as any Europe-wide (or even country-wide, funded by the CAA) implementation? I’ve never heard of such a thing. They have it in the USA.
