If you want to build something that will locate the roving transmitter on
your plot of land that is 300 foot by 300 foot it might not be too hard to
do if you can get your four receivers to do a little bit of timing
computations for you.

Set the roving unit up to send a pulse on a regular basis. It doesn't have
to carry any data or anything like that and it wouldn't have to be too
powerful either.

There are a few assumptions that can be made that are pretty definate.

1. The distance from two diagonal corners of the square is the maximum
distance the transmitter can be from the receiver and still be in the area
that is designated as home.

2. The transmitter should be home. If the calculations are coming out wrong
then the transmitter has violated the bondary of home.

3. All four of the receivers must be set to a very accurate clock so that
they are all using the same reference.


I don't have a calculator with me that will let me do the calculation to
find the diagonal distance across the square so I will use 450 feet as the
rough number for the maximum distance from any receiver.

The first receiver detects the transmit pulse and it is known that the
transmitter is within 450 feet of that receiver. That starts a clock. The
second receiver detects the transmit pulse and the time since the clock
started is noted. The third receiver detects the transmit pulse and the
time since the first receiver detected the signal is noted. With this much
information the position of the transmitter can be determined on a two
dimensional plot. The fourth receiver could be used for a sanity check to
make certain that the transmitter is in the expected location and it would
allow better coverage for when only three receivers can detect the signal.

The space between clock start and second receive detect is the difference in
distance between these two receivers. The next detect is the difference in
distance between the first receiver and the third. And lastly the fourth
detect sets the distance between the fourth receiver and the first. If the
math is done right there will be four circles drawn each has the center at
the corner of your property. When the drawings are made they will all cross
in only one place. There will be other places where two or three circles
cross.

The nice thing about doing it this way is that there is nothing mechanical
and with todays computing power that is available a solution can be had
within milliseconds of the transmitter putting out a pulse.

An idea for the accurate clock could be to use a receiver at each receiver
in the square to receive a local TV station and use the synch pulses as a
reference. Just don't forget the propagation delay is from one side of the
square to the other and figure that in.

Another option would be to put a GPS receiver at each corner and use the
clock from these as your reference.

Or you could use a common receiver site and one clock feeds all four
detectors. Just remember that there will need to be four receiver
antennas and corresponding feed lines to take care of.