Has anyone used a ferrite bead on their coil wire to reduce EMI/RF?

I had read a little about this in Clive james Clynick's book, The White's Surfmaster P.I. Dual Field: "An Advanced Guide". I found a little discussion on the topic on forums but not much. Some Austrailians are using the in the gold fields to cut out interferance from hot rocks. I tried one that I bought from Radio Shack (the 3/8" center hole fits my cable perfect). I mounted it just above the coil. Where you locate it on the cable is suppose to affect how much hi frequency interferance it will suppress. Now for the test, you have to understand that this is on my Whites Dual Frequency PI. I did a simple air test outside away from as much inteferance as possible. I did a test on a nickle and a quarter. I did several tests to get the most depth I could. Now I do know that a PI will not air test nearly so deep as it will do in the ground, but the increase in depth should be proportionate in salt water because of the increase in conductivity. The nickle air tested at 7 1/2", the quarter air tested at 6". Remember the PI is set at as close to stable as you can get it and still get maximum depth. I wish I had take a picture of the setting at the time. So I now snap the ferrite bead on just above the coil. The machine smooths out and quiets some. The DF is a somewhat chattery machine by nature of its power. I now retune the machine to get the best signal. I am able to increse the gain over one fourth of its range to 100% open and reduce the threshold by about one fourth of its range and still get a stable signal. Now the air test...I can easily get the nickle with a solid signal at 11", and the quarter at 8". I know a PI picks up a lot of interferrance from the ground by the nature of it being such a deep signal and am interested in hearing other members opinions and experiences with this type of EMI/RF suppression. I will not get a day off to go to the beach to test this out until this weekend. Also your opinions on if this could help with a VLF machine would be interesting to

I suspect that it will not help a whole lot.

I tried a Radio Shack ferrite core.......that a poster swore worked..........didn't do squat..........lol

I tried it on the F75 and as Tom would say, no joy.

I tried one very briefly, and must admit that I didn't test it well, but from my observations, it did not make a difference on my T2. Also, thinking about it from a physics perspective, I find your finding very surprising and very interesting. Perhaps the PI works a bit differently so I don't know for sure. I like the idea, if only it was proven to work. A video might be cool way of demonstrating your findings, maybe it will stir up some debate.

Maybe a video will be a good idea if I can get a camera and figure out how to send it. I am on a long stretch of work at the moment. I work a 12 hour a day swing shift. Working nights this week, but will see if I can get it done. Now, I got home this morning and did the same test with my two VLF machines CZ6a, and G2. It did no good whatsoever. I had my doubts, but hoped it would help. Maybe around powerlines it would. It does make a diference on my PI machine though. Thanks for your answers and anyone else who has an opinion, I would like to hear it....Stuart

Coil cables are nearly always braided-shield EMI insulated.
In furtherance......any metal placed 'near' the coil........within the coils 'field'.................will cause 'nulls' (weak/dead-spots)............and is not recommended.

Thanks Tom, I was hoping to hear your opinion on this. Since using the ferrite bead is an obvious improvement to stability and depth on my PI machine, does this mean I have a problem with my ciol or the shielding on the cable? Should I send the machine back to the factory for testing? I really hate to do that since it has found gold rings the last two times out and it seems to go quite deep. Your answer would be most appreciated...Stuart

Stuart,

An air-test range of a quarter (being 6") is too poor and indicative of a problem. Same with the nickel. Do you have someone in your area (or on this forum) that can perform a air-test with the same detector.....and see if they have different results. This would be a good direction to start.

Thanks Tom. I have dug much deeper coins and quarters at the beach and know that PI detectors air test badly. But did not know what different coins should air test at. Does anyone on this forum have a Whites Dual Frequency that they could do an air test on a quarter with? I would be greatly interested. I will check with some of the people on treasurenet and see if one of them will also do this, since I frequent that site. Thanks again....Stuart

Stuart,

There is a White's forum on thetreasuredepot and findmall. This may be a good place also.

Thanks again Tom. I found an article on findmall (thanks to a forum member) that really helps. It was a thread by Eric Foster on how to air test a PI detector. I will use his methods of testing. It seem entirely posible that I was too close to EmI/RF interferance. I did not know that once you raise the coil in the air a PI acts as an antennea and will pick up interferance so much from outside sources. If anyone knows about a PI and how it works, Eric Foster would. I am going to air test in a much less energy plagued area and see if and by how much my results improve. I will also do some real world tests at a beach this weekend. Also I have a forum member who is going to do a comparative test with his DF unit. It would be good to have a working baseline to use for an air test...Stuart

Ir took my dual field (sorry I have been calling it a dual frequency) machine into a field today. No powerlines within 200 yards of me. No houses nearby. No power sources nearby. I follow Eric Fosters directions on air testing. Even check the ground to make sure there is no signals that can sway the test. No targets in the area. Put a 3/4" board on the ground to make sure of no targets or interferance that can sway the test. I tried the DF without a ferrite bead on full gain, no pulse, and minamal threshold. I got a reading of 13 inches on a nickle, 12 inches on a quarter. Same settings without a ferrits bead, 13 inces on a nickle, 12 inches on a quarter. No difference what so ever. Changed my mind as to the ferrite bead working to improve depth unless you are in an area that has high EMI/RF. However, I did find that if I so much as touched the cable just above the coil, I would get a loud signal for about a second. On a VLF machine, this is indicative of a coil problem. Does this hold true of a PI unit or is the physics different on this type of unit? As I said I will get more results from other members and will test at the beach this weekend.any opinions would be greatly appreciated. I was wrong in my initial assessment of the ferrite bead, but maybe it will lead me to the understandig that maybe I need to send my unit in for repairs if the numbers do not add up. Hope this thread is not boring you too much, as I am trying to have a machine that I am confident will be on a competitive level with most on the beach. (Tom, I want an aquastar!)

You are not boring anyone. We all try to help each other when we can. Keep asking questions. No matter how 'boring' or 'trivial' you may think they are

Your results are dramatically different..........and more 'correct' now. It does sound like you had bad EMI......or the coil may have been too close to some other metal source.
Sounds like a bad coil cable shield. Do you.........can you...........borrow a coil from someone else.....to see if their coil acts/responds the same....when you lightly tap the coil wire.
Yes.........you would be in for a surprise if we did a head-to-head with the AquaStar........especially on smaller gold. 8uS pulse-delay is a wonderful thing.