Jump to content

Why No Concentric Coils For The Recent Multifrequency Detectors?


Recommended Posts

On 1/23/2022 at 10:50 PM, kac said:

As for Concentrics there are standard 2 coil types Tx outer with Rx inner (reverse wound) and Co-planer where the Tx and Rx are wound flat and the Tx has a reverse wide only around the Rx creating a forced and well defined null.

I'm including some illustrations to help understand the construction (not necessarily the operation) of the different types of IB searchcoils.  First is general, from Lagal and Garrett p. 27 (1979) and note that DD (labeled a) is a specified there are a type of co-planar as is the concentric (d).  Later illustrations below go into some more detail but DD isn't covered:

coil-types.thumb.jpg.37bfda9c850f54fd4c4f97624bbb9da6.jpg

Next three are from Garrett pp. 127, 128, 130 (1985).  I've typed in the figure captions since they didn't scan well:

co-planar.thumb.jpg.47d5b5441dfa5093d3e717382a0e4e69.jpg

Figure 11-4:  ILLUSTRATION OF CO-PLANAR SEARCHCOIL WINDINGS (SAME PLANE).  This illustration of co-planar searchcoil construction shows that the windings are placed one on top of the other and lie in the same plane.  Co-planar searchoils have been in use for several decades.

(Note:  inner circular coils is labeled 'Receiver' and outer coil is 'Transmitter'.)

coaxial.thumb.jpg.9b82fbf8a6986df8280b5375be7f33b3.jpg

Figure 11-5:  ILLUSTRATION OF CO-AXIAL SEARCHCOIL WINDINGS (SAME AXIS).  Co-axial searchcoil windings are placed one above the other with one transmitter winding sancwiched in between two reciever windings.  This type winding placement gives the most uniform detection pattern of all VLF and TR detector types and is affected the least by outside electromagnetic field interference.

concentric.thumb.jpg.fe84a97429c9248c72e26ab278f3c62f.jpg

Figure 11-7:  ILLUSTRATION OF CONCENTRIC SEARCHCOIL WINDINGS (SAME PLANE AND AXIS).  Concetnric searchoil windings lie in the same plane and are centered about the same axis.  This newer type searchcoil is operationally equivelent to co-planar serachcoils.

Here are some details from the text in chapter 11 which may give some details of advantages/disadvantages of different types:

(p. 127):  Co-planar searchcoils are one of the preferred types because they produce very sharp, quick target response characteristics.  These characteristics result in excellent coin and small object metal detection capabilities.

(p 129):  ...Co-axial searchcoils give the best performance in areas of high voltage powerlines and electromagnetic interference.  (cut a sentence)  They are, however, slower response searchcoils.  That is, they produce a slower detector audio "turn on" time when targets are detected.

 

  • Like 6
Link to comment
Share on other sites


Great read, I find DD's have a slight edge in depth but not by much and are quite often difficult to rely on in the iron trash areas I hunt. My detecting started with the tesoro machines and most came with a concentric and then a DD. Just my opinion but Tesoro's really shine with a concentric vs DD. Then came the Multi Kruzer, Which is an awesome machine. I ran the DD's for some time and had Pretty good luck with them until I bought the 9 inch concentric. It was a game changer for the MK. In all fairness the best DD I have ever used was the Nel superfly, oddly it almost seems like a hybrid of the DD and concentric configurations. As of lately I buy up concentric's at a high rate of speed, and fearing they will no longer be available. If I had to pick only one I would always choose a concentric. I wish minelab or someone else would step in and make a 9 inch concentric, I think it would make the 600/800 a machine that would be hard to beat in the performance arena. For now I run my tesoro's with concentric's for clean up in high nail infested sites.

  • Like 4
Link to comment
Share on other sites

When it comes to favorite coils, 8x9 concentric on Tejon, 10x12 on the Tejon for deep hunting fields. The Superfly is a great coil and does incrediblly well on the Kruzer but on top of my list would be probably the Detech Ultimate 9" on the Apex. If they made a 9" for other machines I think they would do really well. It is incredibly emi resistant, very robust but not too heavy and has incredible separation.

9" round is a much better general purpose coil size, probably why most XP users stick with that. I find round coils in general easier to push around in vegitation and undergrowth making it a fantastic coil for woods hunting. In general I think 11" coils are a bit big for general purpose as they are harder to separate targets with in high trash areas, more prone to EMI and just heavier where a smaller coil can make the job more efficient and easier for the user. 11" are better suited for open fields and beaches.

I agree with Dogodog the concentrics do good on the Tesoros in iron infested areas.

  • Like 3
Link to comment
Share on other sites

  • 1 year later...

Agree with comments that the DD coils just do not work as well as concentric for the Tesoro Tejon, especially the larger coils. I use 5.75" coils most of the time due to the trash infested and overgrown areas that I search. The concentric 5.75" does a better job but I also use the 5.75" DD Widescan on repeat trips. The DD can snipe between nails and pick out a few items the concentric had missed. The DD does false on steel twist off beer caps which is quite annoying.

  • Like 1
Link to comment
Share on other sites

20 hours ago, Old Sarge said:

Agree with comments that the DD coils just do not work as well as concentric for the Tesoro Tejon, especially the larger coils. I use 5.75" coils most of the time due to the trash infested and overgrown areas that I search. The concentric 5.75" does a better job but I also use the 5.75" DD Widescan on repeat trips. The DD can snipe between nails and pick out a few items the concentric had missed. The DD does false on steel twist off beer caps which is quite annoying.

Not sure if you tried this but when I hunt with the Tejon with either the stock concentric or if I need to cover more ground that has less iron concentration with the 10x12 widescan dd, I will set primary disc to break on the iron line. I can then use the edge of detection or nose of dd to get that signature crackle that tells me it's iron. Other easy indicator is if target sounds short in disc mode but sounds much larger and smoother in all metal you know it's a big piece of iron.

No matter what machine people swing and no matter what coil size or type it is easy to forget that metal types overlap in range ie aluminum can be from iron to silver, brass can be close to copper and as low as a pull tab. Even thin brass buttons that are deep can be towards the can slaw and foil range.

I always try to get an understanding of the area I am hunting and work as particular depth. Old sites it is good to pull a piece of large iron like an oxen shoe and make note of how deep it was as the majority if not all of your coins in that area will be less than that shoe. Sense of depth you can better judge the modern top trash.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...