Burnt Out about the Manticore

[Diga]

As a primarily urban coin hunter, EMI can too often become a vexing problem. The easy fixes of using noise cancel and changing modes usually don't help. Decreasing sensitivity to the point of serious depth loss is not a viable option. What often helps (but not always) is going to the 6" coil or switching to a single (10 or 15kHz) frequency. Unfortunately, the Nox performance is diminished (particularly in regards to IDing targets) in single frequency. And using a sniper coil in less than busy areas is frustrating.

.

My underline.

For my area's EMI, and from what I've read, most other area's EMI, the higher the SF, the less audible the EMI noise is. I mean, I find any SMF to be much noisier than any SF, but the EMI noise really begins to diminish at around the SF of 15 khz and higher.

The crappy part is, even though the EMI audible noise is gone in SF's, the depth loss remains.

 

[marcomo]

That's been my experience too, Digalicious. I can only remember one time out of what must be several hundred when I mitigated heavy EMI by going to the single frequency 5 kHz option. The lower frequencies are definitely more susceptible to EMI issues.

Usually I can at least somewhat mitigate, if not significantly reduce, EMI equally in either 10 kHz or 15 kHz SF. When one of those frequencies works better than the other, it is usually the 15 KHz option.

One caveat: I have the 600, not the 800. So I can't comment on switching to SF 20 or 40 kHz. I can't envision a scenario with my type of hunting where 40 kHz would be a valid option, but I could see where there might be occasions where 20 kHz would be.

I've given thought in the past about getting the Coiltek 5X10 elliptical coil as a coverage vs. EMI compromise between the two Minelab coils I already have, but just never pulled the trigger.

I owned a pre-DTS F75 for a couple of minutes and I remember it all too well. Compared to that EMI magnet, the Nox purrs like a kitten!

 

[Coin-Saver]

Seems to me the higher frequency you run on the Equinox the better the ID is. I have power lines all around two sides of my yard so I have been experimenting with single frequencies. Started at 4khz and moved up to 40khz. All I can say is it not only runs much smoother directly under the wires but I have found a few things on the other side of the yard that were previously missed running MF. I attribute that to running smoother and ID'ing better. By Id'ing better I mean the numbers might bounce one or two numbers where before everything in that area was all over the place because there is a lot of aluminum bits and small nails there. 20 kHz wasn't bad but at the moment I am favoring 40.

Oh yeah, the two finds that I had missed were a Quarter of all things and a silver bracelet that was open. Go figure .........Those both in theory should have been spotted better by the 4Khz as they were in the part of the yard with very little EMI. Or noticeable EMI anyway. I assume they WERE spotted but numbers were bouncy just like all the other trash in that area

As a result I think the 20khz to 40 kHz range would be a good choice for anyone to use in an area where they had previously used with the Nox in MF where EMI was present. I think Digalicious might just be on to something here. Also I have only done this in FIELD 2 at the moment.

I do like the possibilities of how it looks so far though.


In an area were there is no outside interference I'll use MF, but I think around the power lines I'll go with 40khz from now on.

 

[Diga]

Thanks for sharing that Coin-Saver.

Your post made me realize I completely forgot to mention the other main advantage of using a SF in EMI: A more accurate / stable target ID

I'm definitely going to continue using 40 khz in urban sites, but I'm also going to compare it to SMF in non-urban, low to mid EMI sites.

A couple of possible disadvantages with SF:

1) There's a good possibility that SF's won't perform well in highly mineralized ground. Well, at least compared to SMF. Hopefully someone who has experience in highly mineralized ground can chime in on this.

2) We can't use the Iron Bias control with SF's in iron infested sites. A work around however, could be using a small coil and slowing down, which is what should be utilized anyway. However, I consider a manual iron bias control almost a necessity for iron infested sites.

 

[Diga]

I just did some more testing in my backyard. It's brutal for EMI because of 3 high power lines running parallel to my backyard, and a 240V line running diagonally across my backyard.

All the SMF modes were extremely noisy, and the TID was extremely erratic without even having the quarter in the detection field. I then tried the SF's on an air test with the silver quarter.

5 khz / 10 khz / 15 khz: No change in the noise or the erratic ID.

20 khz: About 50% less noise, and about a 50% less erratic ID.

40 khz: 100% of the noise is gone, and the ID is completely stable.

When I say 100% improvement in 40 khz. I literally mean not a peep of noise, and the ID shows nothing when the quarter is out of the detection field. YAY!

With all that said, there was no significant difference in depth on the quarter in any of the SMF or SF modes. However, due to the stable ID and stable audio of 40 khz, the detection of the quarter was much more discernable in 40 khz. In that sense, the good finds should increase with 40 khz.

 

[marcomo]

Interesting thoughts, Diga and Coin. I'm glad that 40 kHz is working for you but with a high frequency like 40 kHz, you will absolutely lose depth in the ground on higher conductivity targets. A good choice for gold prospectors chasing those little nuggets but not the choice for the deeper silver coins I seek. But if it allows you to mitigate EMI when the lower frequencies don't, then you could make an argument that it's worth the trade off.

Digalicious, I want to ask you what the initials SMF represent. I can figure out that MF is multi-frequency, but what does the S stand for?

 

[Diga]

Marco,

The "S" stands for Simultaneous. Although it might be a misnomer. It looks as though there might not actually be such thing as true simultaneous frequencies. But rather, the frequencies are sequential...but very fast sequential. If so, it's so fast that I don't think it would matter either way.

I'm going out back to an in ground depth test with the single frequencies.

 

[harleyhummer65]

Im burnt out with the Legend struggling with EMI.

 

[Diga]

Im burnt out with the Legend struggling with EMI.

I'm burnt out with harleyhummer struggling with reading comprehension.

 

[KOB]

i'm burnt out with harleyhummer struggling with reading comprehension.

 

[Diga]

Interesting thoughts, Diga and Coin. I'm glad that 40 kHz is working for you but with a high frequency like 40 kHz, you will absolutely lose depth in the ground on higher conductivity targets. A good choice for gold prospectors chasing those little nuggets but not the choice for the deeper silver coins I seek. But if it allows you to mitigate EMI when the lower frequencies don't, then you could make an argument that it's worth the trade off.

Low frequencies for high conductors, and higher frequencies for low conductors has always been "the rule". Yet, I've only found that to be half true.

For example, I definitely experience a major advantage when using a high frequency for low conductors. With the high frequency, I can hit small gold that the low frequencies don't stand a chance on. Yet, that difference doesn't seem relatively equal when it comes to silver. With silver targets, I'm not seeing much, if any, depth difference regardless of the frequency. Which leads me to:

I just tested that silver quarter in the ground, both flat, and on edge. I certainly didn't see any "Oh wow!" difference in depth between the SMF modes, or the SF modes. I *think* the lower MF's and the SF of 5 khz, *might* have went about 1/2" deeper.

 

[LovestheShiny!]

@ Digalicious... the AT Pro I use is Single Freq 15Khz. Yes, highly mineralized ground, black sand, and of course wet sand/saltwater blind the ability of the detector to get much depth. Here in Western or Eastern Montana, the soil is fairly mild, my machine ground balances at about 80-83 and performs really well. I tried detecting Butte Montana couple of times and the ground balance there is 94-95 (out of a max of 99 on the Pro). The single frequency did not do well in that scenario. I suppose there is a reason that town and mines there were called "The Richest Hill on Earth."

 

[Diga]

LTS,

Thanks for that.

I've got really mild soil in my area, and I wasn't sure how the single frequencies would perform in highly mineralized ground.

Jmaclen apparently has highly mineralized ground as well, and if I remember correctly, I believe he said that SF's don't get him any depth either.

Funny thing is, Paystreak is always talking about how hot his ground is, yet he often uses single frequencies with seemingly, no issue.

Perhaps it depends on the type of mineralization and/or the SF being used?

 

[LovestheShiny!]

@ Digalicious... yes, you may have something there regarding what the Single Freq used is. I am limited to the 15Khz with four minor adjustments on the AT Pro, so using that 20 or 40 Khz may allow good depth with none of the EMI problems. Hope that works out and you do well!

 

[Diga]

Thanks LTS.

Yes, 40 khz does work well in my area. I'm just lucky that I don't have highly mineralized ground to contend with. EMI is becoming a real PITA though. Sure, the audible noise can be eliminated, but the depth still suffers significantly. On the occasional times I detect well outside of my city on sites with little to no EMI, the depth difference is eye opening.

Happy hunting to you

 

[Cherry Picker]

I've always wondered about a humbucking coil. It is used on the electric guitar to eliminate the 60 kHz hum. That is why they call it a humbucker. The single coil, like on a Fender, has a nice crisp sound but it has issues with noise. To eliminate, or reduce the noise they take two coils with the exact same length of wire. One is wrapped in the opposite direction as the primary coil and that removes the noise/interference.

Both the detector coil & guitar pickup use magnetic current. I wonder if an exact duplicate of the receive coil could be used in the same way.

 

[Diga]

Detector,

There's a really good discussion about EMI on another forum, but I don't know if I'm allowed to post it. The thread was started by Steve Herschbach in 2017, and he said:

"Changing coils can also have a huge impact as the coil is the main route into the detector for EMI. Smaller coils almost always are better behaved around EMI. Special figure 8 wound "anti interference" coils can eliminate it entirely. The BigFoot coil is EMI immune as far as a coil can be".

He also said:

As a rule, the lower the frequency, the more issues you have with EMI. It is especially bad under 10 kHz. DEUS owners may see significant EMI at 4 kHz, only a little at 8 kHz, and none at 12 and 18 kHz. Another reason why manufacturers favor mid frequency over low frequency detectors these days.

Now that was 5 years ago, and the EMI has only gotten worse. Seemingly now getting into the mid frequency range.

I think the metal detector companies need to seriously address EMI with better coil design and shielding, because the so called "noise reduction" feature on detectors does almost nothing. It does nothing on my Simplex, Vanquish, or Legend. It does nothing on videos I've seen with the Nox and the D2 as well. You see the You Tuber do a noise cancel, and no matter what detector they are using, the noise remains the same after the noise cancel. The funny thing is, never once did any of them say, "This noise reduction did absolutely nothing to mitigate the noise".

Since the "big three" manufacturers are based in areas in which most detectorists are detecting in farmer's fields, etc, with low EMI, they don't seem to realize the severity of EMI for us in North America that hunt urban areas with high EMI.

 

[Coin-Saver]

All of this brings me to another question. Something I have wondered about but have no technical ability to prove one way or another. I was wondering if anyone could shed some light on this though.

In my yard where there is obviously less EMI (most distance away from buildings and power lines) ground balance is ALWAYS 19 to 20.

I move to where the EMI, Noise, buildings and power lines are and ground balance is ALWAYS 65 to 85 depending on the spot and how close to the power lines.

My question is: Does EMI have an effect on ground balance. I had chalked this up to possible fill dirt and a slew of other things but since this was a farm field 40 years ago I'm starting to think EMI is having an effect on the ground balance. I just wanted to know what everyone else thought because I don't remember it being discussed.

As a side note. I know that you will lose depth with a higher single frequency but how much loss will always be debatable in a given area. I just want to mention that in my original post I should have mentioned that the quarter and the bracelet I found were both 2" deep.


It doesn't prove anything at depth but it did prove to me that on shallower targets there is a clear advantage using 40khz over a lower single frequency or SMF in high EMI.
Which brings me to this. How many people have hunted and fought the erratic ID's and noise of SMF in high EMI areas and missed shallow objects?

I am not saying that the detector didn't see them using lower single an multi frequencies. I am saying that in the area I found those two items I believe that with all the small nails and aluminum bits and screws and such the detector just didn't lock on sound wise OR ID wise otherwise I would have dug them.

If I had been digging EVERYTHING I might have already found them but since I'm not a fan of digging a bunch of little screws, nails and aluminum pieces and the detector wasn't as accurate on those settings I just missed them.



All of this is the reason I have always said: You will learn your detector better going over small spots of land that you have pounded to death then you will in a new spot. People get excited when they get a new detector and take it to a new spot and find things. Could be that you could have found it with most detectors. Hunting these small spots that you have pounded to death and finding something new is more exciting to me.

I am one that will run a detector every possible way that I can before I will buy another. I don't feel I NEED another detector until I feel confident that I have outgrown the one I have and that takes awhile with most detectors. If someone is really good with an Ace 250 and buy a Deus II they might have a better detector and better technology But it doesn't mean anything if you don't learn to use it

 

[Diga]

My question is: Does EMI have an effect on ground balance?

That's a really good question, and something that didn't even cross my mind.

All the more reason that at any given site, to bury a deep target and see what frequency(s) ID's it best. It would only take a minute longer to also see what ground balance setting ID's it best. I'll be checking that from now on. Thanks!

 

[Cherry Picker]

Good question.

I have noticed in tot lots I have some that will GB in the 90s, while others GB in the 20s. I don't notice any difference in EMI tho.