Time Difference Of Arrival (TDOA)

Radio communication is always threatened by QRM, willful or errant signals making useful communication difficult or impossible. Traditionally, hams have made a game/contest of finding unknown transmitters and rewarding the most skillful.

A new method of this with technology is emerging, called TDOA. I like to think of it as reverse “gps”. The ultra accurate time signals from gps satellites are used to determine distance from random fixed stations to an errant target station based on time difference to each random TDOA station location.

KiwSdr is already doing this with hf band. One the links below shows how the location of one the infamous Russian numbers stations was found.

http://kiwisdr.com/

https://www.rtl-sdr.com/kiwisdr-tdoa-direction-finding-now-freely-available-for-public-use/

A very interesting application of TDOA principle is for locating repeater offenders. Although rtl2832 base sdrs are generally very poor receivers, they can used for this. If connected to a web sever and digital data recorder, an errant signal needs only to defined by frequency timestamp.

TDOA data from each random rx location at a specific time should yield location within 1ft.!

http://www.panoradio-sdr.de/tdoa-transmitter-localization-with-rtl-sdrs/

I estimate cost of each location (3 required) is less than $100.

Gary Lust ae7ov