Keep in mind the SPP is so much cheaper than any of the ML's one shouldn't compare them. They do well but won't match the much more expensive detectors. That doesn't mean they don't come close, especially when hunting small gold.
If the special coil ever comes to be, the depth of the TDI or SPP will increase considerably.
For those of you wondering about what I am talking about, I posted some info on the TDI and Goldmaster forum about building a DOD coil that worked surprisingly well for depth. The great thing is in my limited experimenting, the coil was self ground balancing and noise concelling, thus no GB required and the audio was extremely quiet. The noise reduction was so great, I could hear signals that were extremely weak. Thus, the depth potential increased greatly.
Right now, I have no idea if the coil will work in OZ or not. If it does, there will still be a down side and that is, only half of the coil will detect close targets, so it will appear only half of the coil is working. In essence, this DOD coil is something lie a "Salt coil" in the fact, there are two windings that are set up to cancel each other.
If you look at the new ML dual DD design you will see a sort of rectangular larger transmit and two separate D receive windings, with one on each side. Well, my idea takes this basic structure but one of the D's is set up for a positive signal and the other set up for an inverted response. The result is cancelling signals. However, when a target interrupts one of the two D's, the signals are different and that difference is amplified. Unfortunately, because the two D's are wound opposite, then one half will act normally while the other will not work right at all. When the signal is deep, then it acts more like a more typical DD coil except the noise level is basically non existent.
The net result is sort of like being able to turn off the GB and use the extra gain without any ground signal. At least, that is what it does here over relatively flat ground.
A somewhat different version of this was tried where both coils were set up to give positive signal and that worked fine also, but GB was required. This coil was tried in really noisy ground and it worked great according to the guy who built it. As I was told, the coil was very quiet and the GB required was a range that was quite wide.
Now, after this long winded explanation, I have a question. Would any of you be interested in a coil that could give you extra depth close to what can be had with the GB off even if it only seemed to work on one side when checking near surface targets? Deeper targets would act more like a mono coil.
For me, it is not a problem, but others may find it something they may not like.
Reg
