Coil questions I haven't been able to find the answers to by searching this forum

[Mike Hillis]

My questions are mainly around the HF coil.

For those of you that have them, are the HF coils changing your id number spread from what the MF coil reads??

For example, using the MF coil that gives a 12 number for a nickel, will the HF coil also give a 12 number for a nickel, or is the range expanded (as I would hope) and instead of a 12, you get...say...a 16????

I guess what I'm really asking is, "Do the coil change outs give a changed meter, or is the meter readings the same for all coils?"

Thanks,

Mike

 

[Andy Sabisch]

Sorry, but the range of the ID is not expanded as you change coils. A nickel should read 12 on all three coils - LF, MF or HF. There may be some slight variations; i.e., 1 segment, between coils but they should all produce similar readings in terms of ID values. This includes some of the test coils I had the opportunity to try out as well; i.e., DD and concentric.

So in answer to your question "Do the coil change outs give a changed meter, or is the meter readings the same for all coils?" the answer would be the meter readings are intended to be the same for all coils . . . . sounds like this is not the answer you were looking for however.

Andy Sabisch

 

[Mike Bearden]

The HF coil will change target readings in some instances, it also forces other changes to accommodate stability more than anything else I've noticed.
It's way more sensitive to small targets, so the sens will be the first thing that has to be dealt with, expect to turn the sens down by at least 3-5 clicks compared to the 7.5 in the same hunt sites.
I do NOT recommend using this coil (in this size anyway) in trashy sites, it'll run you crazy in quick fashion.
However, in other sites where the targets are more spread out and the GB is easily achieved I see nickels reading solid 12's for the most part but dug a V last week that read 15 on the ID and 8" deep, locked solid and didn't sound like trash so I dug it and was pleasantly surprised.
I suspect allot of how the 18.75 will work for you will depend on where you take it and your soil/beach conditions.

Mike

 

[steve herschbach]

Hi,

As Andy says most coin type readings are pretty close between coils, either the same or within one segment. But what I found to be very important, at least to me, is that small non-ferrous items that read iron on the MF coil move up at least a couple segments and into the low non-ferrous area where they belong. This will be extremely important to those hunting small gold items, whether jewelry or nuggets.

For most people the 7.5 kHz coil is probably the way to go, but the high freq coils will see a lot of use on my X-Terra. I just wish it would quit snowing... got 6 inches last night!!

Steve Herschbach
Steve's Mining Journal

 

[Mike Hillis]

That means you don't get the real benefit of the frequency change on a TID detector, namely an expanded TID range based upon the frequency. Sure it will be more sensitive to lower conductive targets, but you still will not be able to tell the low conductive trash from the low conductive goodies any better than you can with the stock coil.

Oh well It will still be fun to learn a new machine and at least now I'll know I don't have to buy that coil, or at least not pay full price for it. I'll wait for the 3kHz coil to come along. Just the low frequency itself pays a dividend in my highly mineralized soil, and the TID range expansion for high conductive targets isn't as valuable as the lower range.

But that is a definite miss by the X-terra 70 engineers. A very disappointing miss to me.

Kind of kicking myself now, though, because it appears I sold the wrong machine to buy an X-70

 

[Mike Hillis]

I got 2" last night up in the foothills, but as I drove down into the valley for work, I saw that not much fell down here. Oh well.

HH

 

[Digger]

Here is part of what I posted:

I found the visual IDs to vary between the coils. Half dollars read 45 on the stock 7.5 Khz coil, but read 42 on the higher freq 18.75 coil. Quarters read 42 on the stock coil and 39 on the higher freq coil. Clad dimes read 36 on the stock coil and 33 on the higher coil. Oddly enough, nickels and zincs are the same on each. In all instances, as I increased the sweep speed and increased the depth, numeric readings became less consistent. Slowing the coil down to what some other Minelab hunters might consider normal, will not respond to some of the smaller targets. The X-Terra must be swept fairly quickly to maximize the potential.

Round tabs read 15 on each coil. Small square tabs read 27 on each coil. But, as I increased the depth, the numbers became jumpy and fluxuated from 24- 27. Larger square tabs read 24 on both coils. Screw caps read anywhere from 18 - 27 on the high freq coil and those tested read solidly as 27 on the stock coil. An old 2 cent piece read 33 on the stock coil and 30 on the higher coil. Several IH cents that read a consistent 27 on the higher freq coil gave readings of 27 and 30 on the stock coil. Silver dimes read one of 30, 33 or 36 on the higher freq coil (depending on the specific dime). But were each one notch higher on the stock coil with readings of 33, 36 and 39. A large men's gold ring read 18 on both coils. Depth between the two was similar at 12 - 13 inches of air. A very small lady's gold ring read 15 on both and the higher freq coil did have a slight edge in depth of detection.

What do I make of all this???? It seems to me that, once you get target numeric readings of 30 or more, the stock coil will provide a reading "one notch higher" than the higher frequency coil. In other words, 45 on the stock coil became 42 on the higher freq coil. 42 became 39. 36 became 33. But, once you got to 30 and below, they were pretty consistent with each other.
The coin depth "edge" goes to the 7.5 coil. Without exception, the stock coil achieved approx. 20% more depth with each coin target. More with dimes. But, less with jewelry.
Sensitivity to small gold jewelry gave an edge to the higher frequency. Not the big rings, but the smaller ones for sure. And, according to the experts, the higher frequency should be more sensitive to smaller targets.


HH Randy

 

[Mike Hillis]

Digger,

Are you sure you don't have the 3kHz coil? Your post sounds like what I would be expecting from one. Perhaps you got one by accident and no one knows

A low frequency would do exactly what you reported. Expand the range between higher conductive targets so that there would be a bigger spread of numbers between them once you start to pass the zinc range. And that is what your post is reporting.

I would be expecting just the opposite from a high frequency. A high frequency would be increasing the spread between the low conductive numbers and the high conductive number spread would be getting tighter.

That is real confusing?????????????????????

HH

 

[Jackpine Savage]

is completely believable. Remember this is a digital machine not analog. The spread Randy saw may be due to other factors than operating frequency, most likely the target windowing that Andy has spoken of. The proof will be in the pudding on the LF coil, hopefully those with harsh ground WILL see better performance on high conductive targets.

Tom

 

[Digger]

Mike, It had to be the 7.5 and 18.75 coils, as these tests were done last December with my X-50. Even if the 3kHz coil as available then, it wouldn't have worked with the X-50. If I recall, someone else followed up my post with one that reflected similar results. If I can find it, I will send it to you. HH Randy

 

[Mike Hillis]

Ok. Appreciate it. And I'll do some more reading tonight. Maybe there is something else going on and somebody has touched on it before.

 

[Mike Hillis]

because of the way high frequency's behave with high conductive targets in high mineralization. Going back to my target wrapping questions earlier. That would help counter the wrap around from high conductive to iron.

Yes, being digital, the designers can make it display whatever they want it to. And it may not necessarily be a bad thing.

I have no doubt that the 3kHz coil will help in high mineralization. But if what I am reading is true, and if the ground supports it, the 18kHz coil may be the better coil for deep silver.

 

[BarnacleBill]

Take a look at my air test, follows Randy's numbers fairly well.

http://www.findmall.com/read.php?55,290751,290751#msg-290751

It's a high frequency conspiracy I tell ya!

HH
BarnacleBill

 

[BarnacleBill]

An expanded ID range is desirable probably on all machines, but I think the designers are constantly fighting target ID stability. More numbers means more ID jumping, with some people wanting absolute written in stone ID's that never waver under any conditions, and that's a tall order.

Now with 3 different coil frequencies, shifting ID's would certainly make a lot of people really crazy. i.e. On the 3 KHz a Jeff=6, 7.5KHz a Jeff =12, 18.75KHz a Jeff=18. You'd have people screaming and running for the exits!

However for whack job beach hunters like myself, I could envisage a special jewelry mode. Push a button and the machine enters a pre-defined notch from the current zero to 25. That range is now expanded like under a magnifying glass set at 4X. So numbers start at zero and go to 100. The numbers from the original range now map to 4 numbers each in the new range. The big question that remains is whether the machine can be made stable enough to keep the numbers from squirming around too much.

I'll soon be sending an invoice to ML for this idea.

HH
BarnacleBill

 

[Jackpine Savage]

Thats alomst as bad as Steve and his notching! Any serious beach hunter knows you only need one tone and NO ID.

tom

 

[Monte]

YES, coil changes can and will cause there to be some noteworthy target response differences, both audibly and visually. You might also want to refer to my post to Christopher, above on the forum, regarding the high-number readout.

As Randy ("Digger") related in his reply, I also found the same types of differences with my X-Terra 50 when I changed to the 18.75 kHz High Frequency coil. That is, the 25

 

[Daniel Tn]

If I recall, you sold your DFX to get the X-Terra 70. For those that don't know about the DFX, what Mike is referring to is the 3khz and 15khz single frequency modes on the DFX.

If you are a jewelry hunter, the DFX can really be tweaked by running these single frequencies. If you run one or the other with "normalization off" it gives you the "raw data" that isn't compressed to fit a specific frequency range. Evidently the X-Terras must be made to compress the raw data into the 7khz form, since all 3 use that coil as stock and standard.

The benefit you get from the ability to change frequencies with that feature off on the DFX, is that if you use the high frequency, you get a very wide range of numbers down in the lower conductive scale. Which as we all know, that's where the gold falls, along with the foil, tabs, and nickels. The DFX can use that to seperate the alloys further apart than they would be if they were compressed. So on the DFX, running 15khz and getting the uncompressed numbers, means you are able to tell alot of gold from tabs and foil from tabs as well. It's not fool proof but to the discriminating detectorist it gives an edge. Pulltabs are made of many different alloys but usually higher than gold, so in this raw data ID, the tabs will read way higher than they normally would if the data was compressed. In all, it's a pretty neat feature on the DFX and one I was wondering about too in regards to the X-Terra 50 and 70. I'm sorta disappointed to hear that about it as well but for me, I think overall I'm going to like the X-70 better than the DFX just for the simplicity factor and not having to worry if it is set up right with filters, sweep speed, yada yada yada. Gonna order my 70 here in a little bit.

 

[Mike Hillis]

I'm digesting all the info. Your information combined with Bill's information gives me a better handle on what they (Minelab) intended with the HF coil.

Looking forward to what dirt does to the reading. I should be able to play with mine tomorrow. The HF coil figured into my Xterra purchase decision as I sold my primary jewelry machine to buy it.

If you thought the Golden was a fun detector and you also think the Xterra's are fun detectors, then I'm pretty sure I'm going to think it is a fun detector, too.

HH

 

[Rick(ND)]

This is one of the best reports I have seen on the coil freq and what they can do for the user. Over all the M freq coil is for every day use and what most people will use. The H freq for those that are looking for the lower conductive targets and if all this is correct as I understand it the L freq coil for the higher freq targets, that we will see once the coil is released, or one of the field tester like yourself post your findings.

Thanks Monte for spending the time to explain this to everyone.

Rick

 

[Mike Hillis]

I like metal detectors and so I try to specialize the machine to the job just so I can use as many as I can. I bought my DFX just for inland jewelry hunting. The only thing, and this is truly the only thing I didn't like about it was the fuzziness of the multi-tone mode. I wanted a clearer tone and was working on a accessory that would change the multi-tone into larger tone groups.

When Sonny told me about the X-70 and I saw the tone options along with the expanded notch range, I saw something that might could be a better fit for the way I like to detect, which is limiting the audio to just what I am looking for. In one place it might just be high foil signals. In another place it might just be the low foil range. In others it might be that small area between square tabs and zincs. All the other noise is just noise when I'm focusing on a particular conductive range which is why I like notches. They get rid of all that extra noise and let me focus on my chosen target range. To me, that is fun.

I had been hoping that the HF coil would work like the DFX and expand the lower conductive range, and I was disappointed it didn't. But after reading Bill's, and then Monte's, post, It looks like the HF coil will still have a positive effect on my jewelry hunting.

The X-70 may also turn me into a one detector man, which would be a terrible thing to me, so I must resist.

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