You don't need directional antennae. Without getting too long winded (I
know, I know...) you monitor the arrival times and frequencies of the
interrogation signals and the replies and combining that with your known
position, you can mathematically determine the positions of all the
emitters. Multiple samples enable the system to determine velocity (a
vector of direction and speed).


wrote in message
...
On Tuesday, December 10, 2013 1:41:26 PM UTC-8, Sarah wrote:

Well, define "accurate", and "could put in a glider".

Fair enough.

If you were able to put TCAS in a glider that would do it, but trying to get
azimuth information off of passive monitoring of radar returns (like PCAS
does) has to be a hit-or-miss proposition (pun intended) since you don't
have the ability to actively interrogate other transponder-equipped aircraft
to string together enough bits of information to get good direction. You are
dependent on ground radar or TCAS-equipped aircraft to do the interrogating
for you which is no always reliable. Some sort of directional antenna added
to a PCAS might help in the way you describe (showing quadrants), but I have
to believe it's not the sort of thing you could really count on and would
totally suck for glider-glider scenarios.

I'd also add that the research shows that no matter how diligent the scan,
see-and-avoid detects not more than half the targets that are collision
threats. Non-threats are much easier to pick up because of the angular
movement of non-collision targets. So, the fact that you see other aircraft
when you are flying to some extent generates a false sense of security -
your are much less likely to see the one that's going to actually hit you.
There are scenarios in the research where successful detection in time to
act is on the order of 10-20%. That gave me some pause.

9B