Thanks Peter.
Can't say I'm particularly interested in the audio warnings but can you describe the specifics of the 'Mode S' detection as against the ADSB? does this provide the PCAS type functionality?
Hi again Vic,
As you will be aware, ADSB provides accurate position information (as does the new PAW Bridge P3i), so the moving aircraft can be displayed on a tablet using SkyDemon, EasyVFR, Runway HD, etc. As you presumably know, raw transponders do not provide any position information except (in the case of modes C and S) - altitude information.
Systems like the PCAS (which I have run myself since 2009) operate by decoding this altitude information and then trying to determine distance to target by interpolating from the strength of the received signal. Even with some very clever mathematical algorithms, however, it is extremely difficult to do this reliably and accurately, principally due to the massive variation in output strength between light and commercial aircraft transponders. The principle criticism of the ZAON products has always been that the reported distance to targets was unreliable. This led to reports of 'false alerts', when the target aircraft was in fact there, but just too far away to see.
As trying to accurately show distance to target from transponders is unreliable, we decided early on not to do so, but instead to simply identify the presence of (at present) mode S aircraft with a simple graphical warning (e.g. in SkyDemon an aircraft symbol centred on your own position and including call sign / ID and relative altitude - other tablet systems vary in the way they display the information). This is then supplemented by audio alerts 'traffic - notice', 'alert' then 'danger' if the aircraft continues to get closer. The use of audio alerts is deliberate to encourage the pilot to look for the approaching aircraft
outside the cockpit rather than on a display screen.We have also provided user selectable 'Mode S Detection Range' settings to cater for flight from sparsely populated (in transponder terms) 'rural' areas to operation in a high density CAT environment. This work is ongoing with further developments expected.
Hope this helps make things clearer.
Regards
Peter
