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« on: November 14, 2023, 2216 UTC »
The length of the coax line can just move the receiving location a few meters. Nothing that counts. This wrong idea comes from the usual combination of identical antennas close to each other for standard goniometry. Once, I set two FM antennas 1 wavelength apart on top of a rotor. All bearings were 15 degrees false, and that was because I did not care to make coax lines of exactly equal length for both antennas to the combiner.
In TDOA, the phase of the RF signal is anything and unknown. What is important is the phase (or delay) of the recovered audio after detection. A difference of 1 millisecond means a difference of distance of 300 kilometers between the TX and the two receivers, thus giving an hyperbola for possible TX locations. With at least a third KiwiSDR (or more), several hyperbolas can be drawn, and where they encounter is the probable place of the TX. Of course, with signals reflected by the ionosphere layers, the hyperbolas should be blurred, and so is the 'point' where they encounter. The error can be much larger when the propagation is quickly changing between daytime and nightime conditions.
BTW, note that only modulated signals can be treated by TDOA. If there is no modulation (or even if the S/N is too bad), TDOA can't do anything. Only the traditional goniometers can give some bearings.
On the other hand, TDOA can be accurate with direct propagation along/just above the ground. And setting a TDOA receiving station is easier than a goniometer station, so FCC (and alike elsewhere) could easily relie on many stations, wherever there is a powerline and an internet connection. Less easy where solar PV panels (and batteries) and radio or satellite links are needed.
As you know, shortwave signals have a short direct range, particularly when the polarisation is really only horizontal. No, an horizontal dipole is not enough to achieve such a goal.
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