Hi Fred,
I am assuming you were following the information posted on the Nuggetshooter (NS) forum regarding my comments about my modified GQ clone.
Now, to my knowledge, the DD coil isn't available yet on the GQ, but it is my understanding the new pc boards have been modified for them. So, the addition of a DD coil is much easier on the newer GQ's.
To the best of my knowledge, the only DD coils in use on the GQ in the US are ones that I built. My dad and I use them and there is one more presently owned by a Paul in CA. He has posted some info about his use of the DD coil on this forum. This coil was originally installed on a GQ owned by a Scott while he lived in AZ. This is the one also mentioned on the NS forum.
Now, I have tried the DD across AZ, in Colorado, and Paul has tried it some in CA. However, it has not been tried in Australia, as far as I know.
There was a post on this forum by a Kev, I believe who built a DD and was using it on a beach in NZ.
The DD coil doesn't make the GQ perfect, but it does dramatically reduce any ground signal, making hunting very easy in most areas. In the worst places, just hunting a little slower usually takes care of any problems.
Now, you mentioned you had problems with the White's PI and hotrocks. I haven't tried the Whites, but on my PI, very few rocks will generate a signal of any significance. However, volcanic rock such as basalt will produce a response. On a mono coil, the signal is quite dramatic. There will still be a response when using a DD coil, but the response will be much less. Also, moving the coil just a little closer or farther from the rock will cause significant audio changes, making it much easier to separate rocks from metal objects.
There are a few rocks that will cause a strong positive response when using a mono that may produce a slight negative response on a DD. I was surprised when I first tested them. These rocks were sent to me from Utah, I believe.
Finally, I have come across a few hotrocks that will generate a positive response on both a DD and a mono, but they have been rare.
The black sand that causes a strong response on a VLF produces little or no response on a PI. I say little, because one may get a small response, not from the black sand, but from when the search coil passes from the black sand to a clay dirt. With practice, such situations can be easily determined.
I was hoping that Eric was close to bringing a DD coil out, but I have heard that there have been problems obtaining coil forms.
I have been reluctant to build coils for other GQ's. The reason is my GQ clone is a little different than ones coming from Eric. As such, building a DD to work well on another PI is a challenge. I would almost need the PI available to assure a proper match.
Another reason is I have been constantly changing little things which has caused me to have to build different coils. So, until recently, I wasn't sure just what I would ultimately end up with as a coil design. I am still not sure I am completely done at this point.
It does become very tricky to build a coil that works properly at 10 usec or less. Damping of the coil becomes very critical. On my PI, I have the initial damping slightly underdamped and I make final adjustments in the coil housing or plug. This has allowed a wider arrangement of coils to be used, but does make mine different than Eric's.
I hope this helps provide more information about the DD and the GQ.
Reg
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