You might check the Geotech1 forum for some answers.
Now, when you built a larger coil, what size did you build and what were you expecting for a depth increase?
Keep in mind that the detector you are trying to build a larger coil is a low powered PI. So, there will not be the maximum depth increase one might find if going to a larger coil on a high powered unit.
Here are a couple of basic rules to remember. One, if the object you are trying to detect can only be detected to about 1/2 the diameter of the existing coil, using a bigger coil will probably lose ground. Two, there will not be any dramatic increase even if the coil diameter changes from 8" to 12".
If you ware using an 8" coil and can detect an object to 7" or so, you might see an increase of about an inch or so when you change to a 11" to 12" coil, providing the increase in noise doesn't overcome the target signal. A bigger coil my go deeper under ideal conditions but it is also a bigger antenna. Thus, one can easily see an increase in noise and this noise my overwhelm any target depth increase.
So, if you are trying to use the larger coil in an area that is congested when it comes to electronic noise, you may find you won't see any or much of an increase in depth potential.
When trying a larger coil, try to keep the inductance approximately the same as the factory coil. One might go a little larger in inductance if the inductance is 200 uh or so, try to keep the new coil the same inductance. If you decide to change the inductance, then increasing to but 300 uh would be the max I would use and seems to work about as well as any inductance value.
Use quality shielding to reduce external noise. Make sure your shielding isn't detected at the delay you are using. This usually rules out aluminum foil and the copper foil tape used for shielding guitars. Copper or silver plated polyester tape usually can be used but such tape is difficult to find. Scotch 24 works well but make sure you have a good connection with the shield wire
Don't over shield the windings either. Some people have used multiple coats or layers of shielding foil when one layer usually will suffice. Too much shielding is just as bad as too little shielding.
Building a coil isn't difficult but when doing so, don't expect dramatic changes and don't make dramatic changes when first starting out.
Reg
