Jump to content
Nugget Shooter Forums

making large coil smaller


robbor

Recommended Posts

Would it be possiple to take a normal size concentric search coil and open it up and just twist the coils into a figure 8 then double baCK ON itself and make a case to make a smaller search coil? I recall the critical factor was inductance and dont know if that would change it.

Link to comment
Share on other sites

Guest bedrock bob

It seems like you could do that with a mono coil. it probably would not be worth the trouble but it seems feasable.

If you did this with a "DD" coil you would get a "DDDD" coil and the machine would simply stutter. Instead of a "weee-wooo" you would get a "ww...we...wwweee..wweeee-ww...wwo....wwwoooo". You would need a deaf mute prospecting partner, a three legged dog, and a pick with a handle on both ends.

Link to comment
Share on other sites

Guest bedrock bob

Eldorado,

One of my best friends and my dearest prospecting partner enlisted in the Marines in 1968. They drowned him trying to teach him how to swim and then resussitated him. It made him stutter. They thought it was so funny that they made him a radio man. That made him stutter worse. When I met him in 1978 he could not speak on the phone at all. That is all the background you will need to enjoy this story.

This fellow bought his first metal detector in the early 80's. After a few days listening to the beeping of a GB1 in really hot ground he was frustrated to say the least. I spent the first four or five days with him and my Garett Scorpion, so there is no use detailing how much gold this expedition was producing. My vote was to go home, especially after four nights of sleeping on the frozen ground and as many days learning to find a nugget with a machine that could not. His vote was to stay, and he asked me to leave him there and pick him up the next weekend.

This old boy is a serious survivor, and I simply would not have considered the reqest form anyone else. He knew what he was doing at everything except metal detecting, so I hauled freight to the lowlands and camped by the shower and a BBQ chicken for a few days. When Friday rolled around I was fattened up a bit and ready to go back out, and of course anxious to see how my buddy had fared in those days in the high desert. I never imagined that he could wear headphones connected to any type of electronic apparatus, but he was REALLY into it when I left him. Frustrsted, but determined...He was going to make it happen!

I picked up some food, some beer, and a few cigars for the hell of it and went into the mountains. Coming down the last grade toward our camp I could see him in the old familiar spot on the side of the hill where we had found the coarse gold with the drywasher. As I got closer, I noticed that there was something different about his profile over there...He seemed to be holding something besides a detector. I stopped short of the camp and walked across the arroyo and up the hill behind him. When I got close this is what I saw...

He had the circuit board of the detector in his shirt pocket, with a wire running to the other shirt pocket where the batteries were. There were two leads coming out of the circuit board and one was fastened to each ear with an alligator clip. He had the coil taken apart and wound in a figure eight and duct taped to his chest below the circuit boards. he had two bicycle spokes bent into dowsing rods that he had fitted into handles made from the lower shaft of the detector pole. He was saying a prayer as he walked across the gound.

When he saw me he grinned really big and started yelling about the gold he found. He dug into his pocket and he had two nice big flakes about half the size of a thumbnail each. Maybe a penny and a half each one. He had got tired of listening to "all that beepin noise coming from those cussed headphones" and in desperation he had smashed his detector on the rocks. He then took it apart and took the internal speaker out of it and buried it withthe headphones. Then he calmed down a little and he felt bad about breaking his new detector. So naturally he improvised and rigged it to just "ESP the signals to me". Instead of listening to the beep, he,"Prayed to god that I would find some gold". Well, he did by golly. Found one right there laying on top of the gravel. Amped him up so much he added a pair of dowsing rods to the deal and found another the next day! Laying right on top of the gravel.

Now, that is the story and I believe the story is true. He didnt find any more gold that way, but I darn sure did. Right in that spot I found my first nugget that day with a GB1, and over the next year I found many there. I even found two laying right smack dab on top glistening in the sunlight. Saw 'em before I even got close with the detector. I found three more in a pack rat's nest. Big uns. The rest were between the surface and the frostline no deeper than 3".

So whenever I hear of someone tearing a detector coil apart and re-winding it I think of my stuttering prospecting partner. The man found a patch with a broken detector that made no sound. He also found 26 ounces in about ten minutes with a railroad spike and hammer too, but that is a story for a different day.

Bob

Link to comment
Share on other sites

  • 3 weeks later...

That's how a salt coil is made. A figure 8 wire in the center and a round wire on the outside. If you watch woodie"s videos on you tube he has a coil wire that he folds into a figure 8 to cut down on interference while testing in the house. You have 2 hot spots on the figure 8, top and bottom. Using the figure 8 is like using 2 small coils.

Link to comment
Share on other sites

Guest bedrock bob

You know sarge, I think that he was talking about bending the coils BACK OVER THEMSELVES instead of leaving the figure eight configuration. In this way there would be the same winding, just 1/2 the size. If you left the windings in a figure eight you would have 2 hot spots, but with the windings laid over themselves I believe it would effectively be a smaler mono coil.

I know very little about it but this is the way I understand it. If I am wrong please correct me for my own info!

Bob

Link to comment
Share on other sites

I did not catch that Bob. Some of the guys over in OZ mess with making coils. Robbor I would check out some of the OZ forums. If I was going to attempt making a smaller coil out of a larger one I would get a junk coil and take it apart. After you see how it's made just make the wire shorter. Robber drop Woodie or Ismael a line.

Link to comment
Share on other sites

Hi Robbor,

Concentric implies two or more windings centered around a common axis. This is one basic design of coils built for VLF's, but seldom made for PI's.

I am not sure of why you would want to try to make the coil you mentioned, but on a VLF coil, the positioning of the windings is critical for the coil to work. Bending the windings would upset this balance and the coil wouldn't work. Also, because the positioning of windings is critical, most windings are epoxied in place, thus making it about impossible to bend or reform such coils.

If you are referring to modifying a mono coil then the concept of making a figure 8 and folding one half back on the other would probably work on a Whites TDI or Eric Foster's GS 5, but most likely wouldn't work if tried on a ML type detector. ML's are very finicky as to what will work and what will not when it comes to coils.

Once again, most coils even PI mono's have the windings epoxied in place, thus making it quite difficult to try to reform them.

As an alternative, you might try building the type of coil you want. It is difficult for a VLF, or a ML PI, but is quite easy to do for the Whites TDI or some of Eric Foster PI's. In fact, I built a coil I think similar to what you mentioned some time back. Actually I tried different size parts of the figure 8 ranging from equal halves to a smaller top half and folding it back into the larger one to see just what happens and how the coil was affected.

This basic technique is something I did to make my first dual field coil. On that design, the folded back part was smaller and shaped into a narrow oval. The result was a large coil with small coil sensitivity to small gold or small targets as well as large coil depth.

Figure 8 noise canceling coils require a separate transmit winding and a figure 8 receive winding. As mentioned previously this design is both noise canceling and ground canceling, and has two centers. Thus targets will peak twice under the coil. This basic design is commonly called a salt coil by the makers of such coils made for the ML PI. This figure 8 concept is also what Whites uses for their Big Foot design built for VLF's as far as I know.

Using a simple figure 8 transmit winding PI coil only results in a noise canceling coil but not ground canceling. That is why Woody used it in his video.

Your idea of modifying a coil is using good thought process. Don't ever give up on it. Who knows just what you may come up with.

Reg

Link to comment
Share on other sites

  • 4 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...