Jump to content

Varying Height And Azimuth?

Recommended Posts

While experimenting with my Gold Racer, I think I saw more stable VIDs by raising the coil and scanning perpendicular to magnetic north. There seemed to be a height that was most stable, and scanning perpendicular to magnetic north tended to eliminate oscillation between very low and very high values.  It wasn't perfect, but it was suggestive.  I'm wondering if anyone else has anything to offer about this.

Share this post

Link to post
Share on other sites

Minelab pulse induction detectors in particular are susceptible to directional swing issues but it is not something normally encountered with a VLF. There is a scientific basis for what you are experiencing however.

Metal Detector Basics & Theory by Bruce Candy

See pages 12 and 13 and in particular the section on atmospheric sources of interference.

  • Like 1

Share this post

Link to post
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

  • Similar Content

    • By garikfox
      These discontinued Minelab products are really cool to look at and read about. I was amazed.
      The Golden Hawk looked cool! Wonder what the Klondike looked like.

    • By Ridge Runner
      If what we see of the face of the Vanquish is true with eighteen notch points then it’s bundled.
       This happens in lower end detectors but not totally true being it came in higher cost detector too  My Sport  wasn’t cheap but it too has the problem of having notch bundle .
       I have the ORX and to cut out anything I start at the bottom and work my way up . Like others I can’t pick what I want delete what I don’t want.
       The only one that we all know that will let you notch out what you don’t want and leave the others is the Nox .
       This is the main reason I don’t like my Sport is because of that. Don’t get me wrong I’d like it to run in more than one frequency but I knew that ahead of my purchase.
        I guess you couldn’t make me happy if you would hang me with a new rope. 
      Just thinking out loud again! So why don’t you do the same here.
    • By Steve Herschbach
      Check this beauty out. Five km range and depths of up to 75 meters. And only $2500! 

    • By pinpointa
      Hi Guys,
      How many detector brands have Mixed Mode.  Thanks in advance.
    • By Andyy
      Just thought... it would be interesting if the technology ever came about where you could run one detector as either a VLF or a PI (orZVT).  What machines would you combine?
      I would go GPZ and Equinox
    • By GB_Amateur
      I started this project 2 or 3 years ago (so long I can't remember).  Spurred on by recent field experiences and also a recent thread on Equinox settings I've finally finished it. I don't know if it's a completely new idea.  I call it a 'test-stand' as opposed to 'test garden' just to distinguish it from the standard test gardens many of you either already have or at least are familiar with.  There are other similar variable depth test gardens out there (seen on YouTube).  This one has the advantage of continuous depth capability.  It also allows 3-d target orientation angle (similar to pitch, roll, yaw of airplane).  It's based upon the 30-60-90 triangle (remember that from geometry/trigonometry class in high school?):

      Here is a sketch which shows how to implement this concept:

      Shown in the sketch, buried at an angle, is a PVC pipe.  A test target can be slid into the pipe a distance 2*d which will result in it being located at depth d.  I used two sections of pipe (ID = 1.57 in., OD = 1.90 in.), side-by-side to allow me to put neighboring targets in the ground with some option of how close the two targets are separated.  Think of this as burying a double barrel (side-by-side) shotgun with the stock end deep in the ground.  All you see are the ends of the two barrels.  The concrete (bag of Kwicrete) locks the pipes in place.  Here's a closeup of those extruding barrels:

      Besides the tape measure (units of inches) you also see a hand-graded scale at left which I'll explain shortly.  Here is an overall view:

      The two PVC caps, attached together, are for keeping water, dirt, and varmints out of the pipes when not in use.  You'll notice a 1.5 in. diameter wooden dowel rod inserted into one of the pipes. More detail on that shortly, but the target is inserted into the dowel near its end and then the dowel is slid into the pipe.  Holes for locating pins (you can see one of those -- gray plastic -- inserted to register the intended depth) are 1 inch apart leading to a depth resolution of 1/2 inch.  (Again, refer to the 30-60-90 diagram to understand the relationship between insertion length and actual depth into the ground -- a 2::1 ratio.)
      Next I show the business end of the dowel rod:

      The black foam fills the chamber and holds the target (in this case a silver dime) in place.  The hole in the dowel is actually lined with a plastic film canister (remember those from 35 mm film days?) which has been modified to conform to the circular cross-section of the dowel and thus be able to fit into the pipe.  The second slightly smaller) large hole was put in there originally for a second target but so far I haven't used it -- likely of limited value.  You can see the registration holes.  The first one has a red '2'  (difficult to see) just above it; the next (representing 2.5" depth) isn't labeled; the third one has a '3'; etc.  These represent the resultant depth of the target when a registration pin is put in that hole and then the rod slid into the pipe until the registration pin keeps the dowel from going deeper.
      Although the chamber packing material can be made up of many materials, I chose ethafoam (polyethylene foam) high quality packing material.  You typically find this in higher end electronics packaging such as with desktop computers.  More commonly it is white but in this case I used black.  I initially cut plugs with hole saw (see next photo) and then trim with a pocket knife as needed to fit the pipe:

      Ok, so now you're still wondering what that specially graded (homemade 'yardstick') is for.  Again, referring back to the 30-60-90 triangle drawing, the 3rd side of the triangle is also related to the depth.  It is squareroot of 3 times the depth.  (Squareroot of 3 = 1.73.)  That yardstick will indicate how far downrange (along the ground surface) that the target is located.  This helps when you get an iffy response on your detector and want to confirm or deny that the surface location of the target is consistent with its depth.  The units written on the scale are associated with the depth of the target.  You can see from the sketch above that the max depth is 15".  The largest common US coin that will fit the chamber (with some force...) is a half dollar.
      I didn't keep track of the cost but it's probably $30 or so, mostly for the PVC pipe and caps and the dowel rods plus a bag of Sacrete.  (I'm counting labor as free.  😁)
      OK, now that I (finally!) finished this test-stand it's time to get busy making measurements.  I'll be posting those here on the forum as they become available.
  • Create New...