Thanks to useful discussion on the
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Garrett Groundhog ADS Schematic
thread, I have mostly resolved this. What I found was this:
* I have three coils - a 3.5" co-axial, a 7.5" co-axial (?? - the phase response as I sweep an object suggests it is co-axial, not co-planar) and a 10.5" co-planar. I don't have a detector connected to them - I'm just looking at the properties of the coils themselves when hooked up to my computer sound card.
* the only way the three can be connected up the same way and give sane responses is if:
Pin 1 = shield and Rx (signal ground?)
Pin 2 = Tx
Pin 3 = Tx
Pin 4 = Rx
* Connecting up as per homefire's observations in the
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Garrett Groundhog ADS Schematic
thread gives a response... but not a consistent one that would let coils be interchangeable.
* Reversing the Tx/Rx circuits compared to what I've just described also gives a response, but a lower one... and I'm guessing you'd want to shield the Rx circuit more than the Tx
The pin numbers are what I read looking into the plug on the coils, and are numbered going counter-clockwise from left down then across up to the right.
Now I'm just left with this mystery: what is wired up inside that allows...
* Interchangeability between co-axial (1 Tx coil, 2 Rx) and co-planar (2 Tx coils, 1 Rx), and
* Gives a response when you cross the Rx/Tx circuits
I really like the response of the co-axial coils (simple phase relationship - easy to write software for) so if anyone knows the internals, I'd love to find out.
Paul.
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http://www.thunting.com/smf/index.php/topic,7095.msg48613.html#msg48613
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