DD coil...Cody

[Anonymous]

Cody,
In your post below you stated that the hot strip down the center is where the flux lines are greatest.
It is my understanding that a DD coil consists of 2 D shaped coils, one transmit.. one receive, that overlap at the center. The transmit field is what generates the eddy surrents in the target and the receive coil of course does the sensing. Since the transmit coil is a D shape it's my opinion the field generated (or lines of flux) are not shaped like a donut (which is the typical representation used for concentrically wound coils) and therefore the area of greatest sensitivity may not actually be in the center strip where the 2 coils overlap.. ie: a design compromise needed to accompish what DD coils were primarily intended to do which is handle bad ground conditions. DD coils certainly have advantages in trash and for area coverage as well but, I feel that perhaps you should rethink your theory.
Tom, A big fan of the single frequency Musketeer Advantage equipped with a DD coil!!

 

[Anonymous]

Jack, I really have looked very little at coil design. I have the patent on the design of the Minelab coil and will look it over. I do know the electromagnetic footprint of the stock coil is huge compared to the coil. I have never used such a hot small coil so really like it. I will use the Sovereign when I want a larger coil as it is already on the detector and I don't have to switch the coils on my Explorer. I understand the basic D design and for a concentric but that is about it.
I am glad you brought this up as it makes one wonder about one side of the D being a TX and the other side a RX. Do you know which side is which looking down at the coil?
I have wondered about the after market coils as there are some really good reports on some of these. I have seen some post by people that are very knowledgeable in this area. I talked to one engineer and he remarked that we use only about 20% of the effectiveness of the coil due to how we sweep the coil. I was amazed at that statement and thought it had to do not keeping good coverage, height, and the like but did got off into something else so have have been wanting to talk to people that have expertise in that area.
Have a great Sunday,
HH, Cody

 

[Anonymous]

Cody,
I don't know which side is which and if it really matters. When I bought the Advantage I picked up every coil that was available for it at the time the ML 8" &10", 12.5" Detech Accel, and the WOT. After testing I kept the 8" ML and 12.5" Accelerator. the WOT was too big for my sites and the weight also was a killer for me. The 12.5" did everything the 10" could do and more.
In a lot of instances I can believe what the engineer told you and would like to hear more on the subject.
Overlap of course is the main consideration and I strongly feel that even using a DD design a 50% overlap is very important. Another big consideration is ground signal pickup, raising the coil a couple of inches over severe ground drastically reduces the ground signal without much loss of the target signal. I was told that a low coil height in bad ground increases the ground signal pickup by a much higher order of magnitude than it increases the target signal strength.
Tom

 

[Anonymous]

Tom,
I have spent a lot of time thinking about various coil configurations, including my own designs. I am very intrigued to hear your thoughts on the "one D coil as a transmitter and another D coil as the receiver, with an overlap in the middle". Can you tell me where you got that information.
HH,
Glenn

 

[Anonymous]

Tom,
I agree with you overlap is very important even with DD coils especially in iron. I have had some deep coins that only hit in the middle of the coil. Even though the center strip of the coil is supposed to be about equal in depth the whole way across.
-Bill