If I recall, the "four way DF'er" was a left/right TDOA
box with two sets of antennas. If so, this isn't
really a Doppler project (though I could be mistaken...
I can't remember the details of EVERY project I've read!)
There are many TDOA circuits, ranging from simple to
complex. My current favorites would be those using
a CD4066, CD4053 or similar switch for the phase detector, though I've never actually gotten around to
building one. But most of the circuits will work
reasonably well, as long as they have the left/right
indicator. The best way to start with one is to
attach it to a single set of rotatable antennas so you
can use it hand-held for portable, or stick the
antenna mast out the window for mobile operation. They
are quite easy to use, and in an open area such as a
park they can give excellent bearings and are one of
the fastest methods. But they can be confusing in areas
with lots of reflections.
The RIGHT/LEFT/FORE/AFT method is useful when the
streets are at right angles because there are many
combinations that will get you to the target in the
same distance. But in areas where streets are less
tidy, I prefer something that will allow me to take an
actually bearing, not just resolve which quadrant the
signal is coming from.
For actual doppler circuits, I suggest a visit to thewww.HomingIn.com
site - check the "Projects" and "Links"
for several Doppler projects, as well as K0OV's wide-range
Doppler antenna. The Roanoke Doppler may not be the
"best", but it is reasonably well documented and there
are circuit boards available for it. A lot of people
have started with one, then moved on to a more elaborate
version (and/or designed their own).