On Tuesday, December 10, 2013 10:19:07 AM UTC-8, Dan Marotta wrote:

Maybe someone should develop a device like the MRX PCAS which detects
transponders and includes azimuth in addition to range and elevation. Most
of the algorithms have already been developed. There are well established
methods for very accurately locating a transponder. Look up ASDE-X, for
example (LAT/LON/ALT derived from transponder replies). Alas, I suspect
development cost would far outweigh expected return on investment.

I looked it up - ADSE-X is an active radar system that uses either a rotating or phased array antenna (apparently normally mounted on top of the control tower). It's not the sort of thing you'd find you could fit in a glider - even if it were legal. Here's a long to a schematic of the Raytheon version:

http://avstop.com/stories/asde.html

I am not aware of any system you could even adapt to put in a glider that would allow you to get accurate azimuth information off of transponder returns - even in theory.

9B