# Antenna for Resolving 180° Ambiguity with Direction Finding

Discussion in 'Wireless & RF Design' started by jpanhalt, Oct 1, 2016.

1. ### jpanhalt Thread Starter AAC Fanatic!

Jan 18, 2008
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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

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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If the wavelengths of interest are short enough, would a parabolic reflector help?

3. ### jpanhalt Thread Starter AAC Fanatic!

Jan 18, 2008
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It is at 500 kHz (600 m).

John

4. ### Alec_t AAC Fanatic!

Sep 17, 2013
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I guess you don't have a ~1200m diam dish .

Jul 11, 2016
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