Improving Ground Returns......

[CYYZGUY]

Since ADS-B is line of sight, how is it possible that some ground returns still get picked up?  As most of you know I live relatively close to the airport (CYYZ in Toronto), but certainly not line of sight to aircraft sitting on the ground.  I have many trees, houses and other small buildings in my way.

I also find the larger aircraft, usually say a Boeing 767 and up seem to put out better ground returns.   I assume this is because they are slightly higher off the ground....

can anything be done antenna wise to improve the ground returns, or not really?

I will say, after I changed out my PL-259 connectors to N-Type, the sensitiveity did increase and I am getting more returns in general, including ground.

best regards,

Jason

[Runway 31]

Jason,

On the ground the aircraft weight on wheels switch puts the Mode S into Ground Mode. This stops the transponder from replying to air surveillance radars which do not want to see you on the ground, but still allows MODE S surface movements systems such as ASDE-X to track your aircraft on the ground.
 
The surface system does not want the aircraft to squawk at the gate because the proximity of buildings and moving vehicles can cause false tracking to occur. At the same time, if you leave the transponder as it was while flying you are now using an unassigned Mode A code which may have already been reassigned to another flight at the same airport.
 
Once upon a time leaving the transponder on was used as mitigation against aircrews forgetting to turn it back on and so becoming airborne without TCAS protection; but that was before ground systems that tracked transponders. Another way has to be found to mitigate that problem and I believe most aircraft now have TCAS OFF warnings on the dashboard.

The link here gives some additional information fron Amsterdam Schipol regarding ground movements  http://www.lvnl-ohd.nl/ATC%20Fact%20sheets/AFS%2007%20Transponder%20ground%20operations.pdf

I dont know whether the info gives an answer to your question but I hope it helps.

Googling mode-s ground operations will probably give you loads more info.

Alan
 

[CYYZGUY]

Thank you for the information and link.   Very useful reading!

regards,

Jason