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Hi Ray,
Something your wrote bothers me. Here is what you wrote; "This is using a 2 coils one for transmit and one for receive. I dont need to damp the receive coil. 21 turns of #30 enameled wire 8 inch diameter."
Now, I am not sure just what type of coil you built. Is it a DD or something more like a concentric? Did you modify your PC board by cutting the trace going to TP 2 so you can use a separate receive coil that is not connected to the transmit coil?
Also, you said you don't have to dampen the receive coil. Something is really wrong if you do not have to dampen it. Without a damping resistor, the receive winding should oscillate for some time.
If you are uncertain of what I am talking about, here is a link to a pic I posted quite some time back.
http://thunting.com/geotech/forums/s...ad.php?t=10729
You will see by looking at the pic that TP 2 is now isolated from R11 and the transmit winding. The receive coil will then connect with one leg connected to the ground just like the transmit winding, but the other leg will now connect to TP2.
Now, on my pic of the simple schematic, I screwed up and didn't show the receive damping resistor, so I have drawn a new schematic and attached it.
If you really have a separate receive coil and you have cut the pc board so you can operate a totally separate receive winding, then you will have to have a damping resistor across the receive winding. On a DD coil, a 1.2K damping resistance mounted across a 300 to 450 uh coil works just fine. I normally do not put the damping resistor in the coil winding but place it in the connector. This allows me to seal to coil housing and still get to the resistor should I decide to change it.
Now, if you have completed the DD mod correctly, you should be able to reduce the delay even more.
Typically, you should be able to detect a nickel at about 12" or more and a solid nugget the size you are using to test at about 6" or more.
What are you using for shielding of the windings and how are you connecting the windings to the shielding and to the detector housing? The reason I ask is you do not want to have the transmit and the receive have any connections to the other in the coil housing. The transmit should be totally isolated, even at the shield connection in the coil housing. The shields will tie together at the pc board, or at the coil connector at the earliest.
Reg
Something your wrote bothers me. Here is what you wrote; "This is using a 2 coils one for transmit and one for receive. I dont need to damp the receive coil. 21 turns of #30 enameled wire 8 inch diameter."
Now, I am not sure just what type of coil you built. Is it a DD or something more like a concentric? Did you modify your PC board by cutting the trace going to TP 2 so you can use a separate receive coil that is not connected to the transmit coil?
Also, you said you don't have to dampen the receive coil. Something is really wrong if you do not have to dampen it. Without a damping resistor, the receive winding should oscillate for some time.
If you are uncertain of what I am talking about, here is a link to a pic I posted quite some time back.
http://thunting.com/geotech/forums/s...ad.php?t=10729
You will see by looking at the pic that TP 2 is now isolated from R11 and the transmit winding. The receive coil will then connect with one leg connected to the ground just like the transmit winding, but the other leg will now connect to TP2.
Now, on my pic of the simple schematic, I screwed up and didn't show the receive damping resistor, so I have drawn a new schematic and attached it.
If you really have a separate receive coil and you have cut the pc board so you can operate a totally separate receive winding, then you will have to have a damping resistor across the receive winding. On a DD coil, a 1.2K damping resistance mounted across a 300 to 450 uh coil works just fine. I normally do not put the damping resistor in the coil winding but place it in the connector. This allows me to seal to coil housing and still get to the resistor should I decide to change it.
Now, if you have completed the DD mod correctly, you should be able to reduce the delay even more.
Typically, you should be able to detect a nickel at about 12" or more and a solid nugget the size you are using to test at about 6" or more.
What are you using for shielding of the windings and how are you connecting the windings to the shielding and to the detector housing? The reason I ask is you do not want to have the transmit and the receive have any connections to the other in the coil housing. The transmit should be totally isolated, even at the shield connection in the coil housing. The shields will tie together at the pc board, or at the coil connector at the earliest.
Reg
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