Trasponder C mode

[tfede]

Hi,

does the system detect also trasponders in C mode (only ID+Height) ?

Federico

[The Westmorland Flyer]

No, at least not at the moment. It is looking for ADS-B traffic only.

[DavidC]

There are two reasons why it won't work with Mode C

a) Transponders with Mode C only transmit in response to a radar scan. So if out of radar coverage (eg below 3000 feet in much of the UK), they don't emit anything at all.

b) Mode C doesn't include any position information other than altitude, whereas ADS-B includes full GPS position and other data (eg callsign). So in order to know where the signal is coming from, you need some expensive antennas and electronics that can detect the direction and estimate the distance based purely on signal strength. There are some TCAS/TAS systems that can do this, but you'd be looking at £10K+ for anything including useful directional information. The cheaper portable units (eg Zaon) were said to have unpredictable performance.

So we really need more aircraft to be fitted with any/all of ADS-B, F***M and PilotAware to be able to track other traffic inexpensively.

[The Westmorland Flyer]

b) is the principal issue in my opinion. I routinely fly in airspace where there is no radar service on offer yet it is rare for my transponder to show no interrogations at all, even below 1000ft. Just because there are no service providers doesn't mean that there is no radar coverage.

FWIW I think that ADS-B will become the system of choice in the fullness of time. Position reporting systems such as P3i and Fl*** which use the license-free ISM band will always be limited by legal power constraints and the need for yet another antenna capable of seeing the whole sky. As relatively few GA aircraft have transponders with extended squitter capability, let alone ADS-B in, I suspect that time is still well into the future. In the meantime, PAW looks like the best option.

[ianfallon]

Yes - it's a cheap gateway to ADS-B in (and 'out' if you have a mode S transponder) available right now.

The peer to peer transceiver side is a great bonus and should give a nice solution for non mode S aircraft until the ADS-B panacea arrives!

[Robski]

Wouldn't it be nice if we were allowed to let PAW transmit ADS-B messages!

I suppose I can see why this might be frowned upon - the integrity of the whole ADS-B infrastructure would be at the mercy of bods with dodgy soldering irons and limited understanding - but the counter argument is what is the point of ADS-B if it is too expensive for small aircraft to be able to participate in!

Rant over!

[Admin]

Wouldn't it be nice if we were allowed to let PAW transmit ADS-B messages!

I suppose I can see why this might be frowned upon - the integrity of the whole ADS-B infrastructure would be at the mercy of bods with dodgy soldering irons and limited understanding - but the counter argument is what is the point of ADS-B if it is too expensive for small aircraft to be able to participate in!

Rant over!

Hi Rob,
anyone else pitch in, but I am pretty sure you will be able to do this, once I get the code resurrected to provide NMEA messages out to the transponder.
I understand the rules are now relaxed so that you can do this SO LONG as you set the integrity level bit accordingly on your transponder.
Thx
Lee

[Richard]

Just got the reply, Does this help on the rules.

"We will add your name to the list of participants.  You will need to follow the LAA process for implementing the minor modification and you must check the SIL and SDA of your transmissions are set to zero.  This would normally entail a test flight within the NATS’ ADS-B coverage, which is south and east of lines from Bristol to Stafford then across to Skegness, however, NATS are working with the LAA and the CAA to determine how we can perform a nationwide check."

Now to get the installation signed off and I'm good go for the testing.

[Robski]

I was thinking more of having a home made ADS-B transmitter without the need for a commercially supplied mode S transponder, but your point is well taken.

[The Westmorland Flyer]

It'll be interesting to see how all this pans out.

Using extended squitter in SSR transponders for ADS-B was a bit of a cludge in the first place. It was just a convenient way of using a frequency that was already allocated to aviation and could relatively easily be adapted to support ES, thus enabling existing aircraft infrastructure to be used. In the US there is already concern that ES will result in too much traffic on 1090MHz and they are proposing a separate, non-SSR frequency of 978MHz for GA aircraft.

If that were to be adopted here then it would open up the idea of an ADS-B only transceiver, which could be produced far more cheaply than a Mode-S + ES transponder. Such a unit would not need any user controls, therefore requiring no panel space and could be put anywhere in the aircraft within reason. It would still need an external antenna and probably have a transmit power in the 10s of watts PEP level, rather than a few hundred mW. It's the sort of thing a company like Trig would jump at.

[dougblair]

The Reply

"This would normally entail a test flight within the NATS’ ADS-B coverage, which is south and east of lines from Bristol to Stafford then across to Skegness,"
Long way for Westmorland Flyer to go for a test and me from Mona.  Inverness
Is interesting.  If FR24 and  Pilotaware can do better than this there must be an opening for a feed to NATS.  The potential of a large amount of receivers gives potential for error checking on a grand scale.

Lee is it possible to decode enough of the ADS-B for the web interface to identify the target ( reg or hex ) and display the long and lat and altitude that is being sent out ? This would make for a useful piece of test kit.

Doug

[bryannortje]

Hi Lee

I am eager to get the PAW NMEA messages output to input to my FUNKE TRT800 Mode S trnspndr so more than willing to be a tester for this for the PAW community.....

Cheers
Bryan

Ps: you expect it to be in the next software release ?

[Paul_Sengupta]

If that were to be adopted here then it would open up the idea of an ADS-B only transceiver, which could be produced far more cheaply than a Mode-S + ES transponder. Such a unit would not need any user controls, therefore requiring no panel space and could be put anywhere in the aircraft within reason. It would still need an external antenna and probably have a transmit power in the 10s of watts PEP level, rather than a few hundred mW. It's the sort of thing a company like Trig would jump at.

This is what the NATS LPAT device does if I understand it correctly, albeit still on 1090 ES.

[Admin]

Hi All,

There was a question a while back about handling bearingless traffic.
I am at least partway forward in showing something ...

I guess the question is what should the limits be set to for relative height ?
the rings can be displayed as Red/Amber/Green so three height levels could be used.

[rg]

What sort of range can you detect targets out to?