Transmitter Hunting using TDOA: Time Difference of Arrival

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Byon Garrabrant N6BG shows off the TDOA antenna which he built. This is used to find the physical location of a transmitter. The antenna uses a yard stick as the main body of the antenna with two fold out whips on each end. Through the use of a PIC microcontroller a tone is generated based on the synchronization of signals detected by each side of the antenna. When the signals are equal, the antenna will be pointing at the transmitter.

[@n9eerptr]

This is Doppler DF unit developed by the Germans in WWII. In WWII the ship receivers did not have RF front end amp so the LO would go back up the antenna and radiate. Germans knew Allied ship freq and radio being used so could determine LO freq and listen even when ship was not transmitting. I am sure with WWII tube tech it was large unit. I built about 10 years ago using 555 and PIN diode switching. Also there are manuf that do make with 4 or more antennas with diplay and do not have to turn the antenna array. Coast Guard in Florida have units on their boats and also array on towers for locating boats in need. Does work great, even the 2 antenna version. Works with FM rig and listen for tone null to determine direction. There are many articles in QST, CQ and older mags on this unit. Has been very popular unit for DFing. I am sure the FCC has some.

[@harrymagooslum5770]

Yes, you are correct. It's "doppler" or "phase difference" but too many people try to label this TDOA. In the truest sense, it is not.

[@davidbird8204]

Hello do you sell the signal finder as a kit . If so how do I buy one and how much are they

[@iforce2d]

2:21 Phase goes up? Phase goes down? You'll know that one side is closer? I don't follow the reasoning. As long as you only have two points to compare, there will always be ambiguity right?

[@patrickjeromeobaldo2450]

One way for this to work is to use one element as the front, the other as the rear element. Measure the time it takes for each to receive the signal. The rear element should get a delayed signal, equal to it's distance, from the front element. This way, it eliminates the problem with the Equidistant TDOA method.

Would it be possible to find CW transmitters with horizontally polarized signal using this setup?

[@roidroid]

Bit confused why he didn't use 3 antennas to start with, you wouldn't need to spin it, but you would need to add some sort of display to communicate the result to you (ie: a rotatable arrow). But his way, you don't need an arrow, it's just the direction you're standing, simple.

[@AhmedElAtari]

Nice... Keep Up