Antenna for Resolving 180° Ambiguity with Direction Finding

Thread Starter


Joined Jan 18, 2008
This question is related to my studies of the AS3935 lightning detector. I spent an inordinate amount of time getting my emulator to be reproducible and predictable. It is finally there, I think. So, I built a test bench to see whether the "arbitrary" strength value reported by the AS3935 (registers 4, 5, and 6<bits 0-4> = 21 bits total) could be used to determine the direction of a strike. Preliminary results are encouraging. Here's a picture of my test fixture:


Sorry for the darkness. My camera is misbehaving -- or maybe it was just the Michigan/Wisconsin game.

Anyway, pointed directly at the receiver, I got an average intensity value of 20482 (n=3, range ± 230). That reproducibility really pleased me (distance readout was 11 km). At 45°, I got 15750 (n=3, range ±400), distance readout was 14 km changing to 11 km. (The AS3935 uses an adaptive algorithm based on history that is proprietary. I can bypass it by clearing the appropriate register.) Using the arc-cosine function, that result is good enough for me. Of course, there will be a 180° ambiguity. I am familiar with ADF and the use of a sense antenna to resolve that ambiguity.

My question is whether there is any other way to resolve that ambiguity without using a "sense" antenna as is used in ADF's? A method using, say, a third receiver with a ferrite loop antenna would be perfectly OK with me.

Regards, John