Performance Of Small Coils On Gold With The CTX 3030?

[Roughwater]

3 hours ago, PhaseTech said:

Here's a bit of test I did some time ago. Air test, so ground results could be greater or much less depending on many variables.

Thanks.

Actually I had viewed your test already as it was one of the posts on the Thread that Steve recommended I view. Now I am wondering how the 6" smart coil compares to the Joey?  If I were to buy a small coil for my 3030 I would probably only purchase one or the other.  I think Steve may do a test in time between the 2 coils which I'm interested to see when he does. 

[Zampano]

22 hours ago, Steve Herschbach said:

The CTX 3030 is far from being a machine to buy just to go gold prospecting. However, people that own them have had success finding gold nuggets with them in trashy areas. There are some pretty amazing gold nugget finds with the CTX documented on this forum. Lets face it - you can find gold with any metal detector as long as it is large enough and shallow enough. The CTX 3030 would not normally be on my list of preferred nugget detectors but at the same time if it was all I had I would go find gold with it. I will probably try and find a nugget with mine this summer just to say I did it.

There is a long pre-existing thread on the subject on the forum at 

 

Sorry, but this does not leave a lot of hope for the CTX with smaller nuggets than Ron's ; )

 

[Steve Herschbach]

Nobody here is making the case that multi frequency detectors are really hot on small gold (2020 edit - this is no longer true with Equinox). They are not and it has never been the case. All VLF detectors made specifically for gold prospecting operate at a single frequency for a reason. An X-Terra 705 is a better gold prospecting detector than a CTX 3030 and for almost $2000 less.

Early marketing of multi frequency machines talk about incredible frequency ranges and imply all the frequencies are running at full power and actually doing something. The CTX is said to operate at 28 frequencies ranging from 1.5 kHz to 100 kHz. People see 100 khz and think "wow, that has to be hot on gold".

Thankfully Minelab seems to have backed off the multi frequency marketing gobbledygook somewhat. We have to focus on the reality of what the machines do and how they actually perform and ignore all the other stuff. The fact is that multi frequency machines in actual use act like lower frequency VLF detectors. They are optimized for coin detecting and the major benefit of the multiple frequencies is A. exceptional target id accuracy and B. the ability to ground balance to salt water and mineralized soil simultaneously.

The machines do very well on jewelry but when gold items are under a gram performance drops off rapidly. And while the multi frequency designs push accurate target id to great depths absolute all metal depths are lacking. For both these reasons multi frequency detectors weakest performance area tends to be gold prospecting. Nothing is perfect at everything.

[mn90403]

Steve is right of course.

I have a 3030 that I use more than any other detector.  Others I have are an Explorer SE Pro (still very good and close to 3030), 7000, 5000, 2300, GB Pro and White's 6000 DI Pro.  Its strengths are discrimination and accurate target depth depiction. 

The 3 coils I have are 6, 11, 17 and as the size increases so does the depth you can find gold rings and coins.  Shape is important to the 3030.  It is better on man made shapes than natural shapes.  It is also really good at telling you when something is iron (you can dig it if you like).

Goldhound has the best information and programs on Steve's forum that I have read.  His most memorable point is 'don't use a 3030 to find gold nuggets unless there is high trash!'  If there is low trash then there are many better choices.  

That being said last year in the Yuba river I used the 11" coil because I didn't have the 6" coil and found an 18g nugget (the only one with the 3030 so far) about 3" down in clay at the edge of the water.  This river had/has lots of trash and the signal I got at the nugget was 'iffy' but not iron so I kept digging at it.

California Gold has the best pictures of nuggets I've ever seen found with a 3030 and he also found some nice gold coins at an old mining camp with lots of trash.

The 6" coil is something I have not used much yet but its advantage to me is the size.  If there is lots of big or even small trash around then the 6" will avoid some of it.  I've found some coins with it but haven't used it at the beach because I want greater coverage.

I have more 'fun' with the 3030 than any other detector even tho now I'd rather find a nugget.

Mitchel

[Don71]

Hello Steve,

Have you had a chance to compare the 6" Smart Coil to the Coiltek elliptical coil yet?

Thanks,
Don

[Steve Herschbach]

I will do that today!

[Steve Herschbach]

OK, this was a bit of a rush job but here goes.

I used a 4 grain (480 grains per Troy ounce) or 0.25 gram gold nugget. The nugget is from Alaska, slightly flattened and about 850 fine (85% gold).

My main quickie test is my "Bic Pen Test". For many years in a retail environment I have found the perfect small test item to be a cheap Bic pen with an all plastic barrel, and brass tip with 1mm tungsten carbide ball. A "med/moy" or "medium" point. The plastic barrel serves to keep your hand from affecting hot machines like a Gold Bug 2 or GMT. Papermate has an equivalent all plastic pen with a small brass tip. The nice thing about these is they are a standardized test item, and easy for anyone to obtain. I use the pen to quickly and easily separate detectors that might be able to find gold nuggets from those that can't.  In a nutshell, if a detector can't hit the ballpoint, it is not going to do well as a small nugget detector. Most coin detectors you can sign your name on the coil and get no signal. All modern VLF detectors sold expressly for nugget detecting pass this simple test. This is a perfect example of using air tests to determine what detectors can't do as opposed to what they can do. The small brass/tungsten ball roughly simulates the signal one might get from a 1 grain (480 grain per Troy ounce) small gold nugget.

Tests were done in Coin Mode, Ground-Coin setting, sensitivity Auto +3. Manual is probably better but I run Auto +3 a lot so that is what I used for the test. My rational for air tests is different than most. I am not trying for optimum air test, but trying to figure out how things might go in the real world based on my past experience. Hot air tests chasing whispers are the metal detecting equivalent of high grading yourself when prospecting. I try to keep it real, which means when you read my tests anyone should be able to easily replicate them and usually exceed them.

First, the Coiltek elliptical, which is a 9" x 5" DD coil despite having 10" x 5" printed right on it. The Bic pen gives a warbly signal directly on the bottom of the coil, a borderline pass. The coil hot area extends the length of the coil about an inch short of each end, for about 7" of ground coverage.

The small nugget gives a good signal to about 1/2" to 3/4" down the length of this hot strip, with almost no real increase at the center. In my air tests I do not deal in whispers but signals I feel I might be able to get in the ground. I am comfortable with saying I could hit this nugget at about 1/2" and possibly deeper in real world conditions. Nugget target id is a bit flaky but 12-01 is where it settled most often.

I also tested my wedding band, a simple plain men's 14K gold band, for a good signal at about 10". Just for reference a U.S. nickel reads 12-14 on the CTX, my ring 12-29, and a U.S. copper plated zinc penny reads 12-37.

Next up Minelab 6" round DD. This coil is kind of a mini "butterfly" coil. It is 6" wide but the DD "strip" that runs the length of the coil is really only 5" from indent to indent. These tests further put the actual "hot" portion of the coil as being 4" long from front to rear.

The Minelab 6" coil did better on the Bic pen test, to the point where I think I could hit a nugget weighing less than 4 grains in the field in milder ground, but I would have to be right on it. The 6" coil also gives a much more confident signal on the small nugget along this 4" strip than what is seen on the Coiltek coil, with depth near center easily double at 1" to 1.5". I could easily hit this nugget at about an inch or deeper in the real world with this coil. My gold ring, on the other hand, was only seen well at about 8", or 2" less than the Coiltek coil.

This all fits standard small coil theory, as long since illustrated by Gordon Zahara with this chart referring to the Fisher Gold Bug 2:

Source - Field Testing the Gold Bug 2 by Gordon Zahara

Note that in this chart the Gold Bug 2 is blowing the CTX 3030 away for responses on small gold. There should be no surprise there for anyone.

What we see is big coils go deeper on large items, and small coils actually get more depth on tiny items. For every two coils, there is one items size and weight that both coils will hit the same, the "crossover target". Items smaller than that item will be hit better with a small coil, and targets larger than the crossover item will respond better with a large coil. The 6" coil does better on the small nugget, the Coiltek coil better on larger items - where the crossover is I have yet to determine, but at a guess for gram size and smaller the 6" would be my preference.

That said, there is the elephant in the room that some of you may have already caught. The Coiltek covers about 7" per sweep where the 6" coil only covers about 4" per sweep. This is a very substantial difference, and this along with the solid bottom design tends to actually lean in favor of the Coiltek coil for general nugget detecting, where larger nuggets may also be found. You give up a bit on small gold, but gain on larger gold and gain greatly in ground coverage. Personally I would use the Coiltek coil as my standard nugget hunting coil on the CTX 3030 and reserve the 6" coil for specific patch work.

Final note - the Coiltek coil was picking up misc EMI during tests at my house, 6" coil was quiet as a mouse.

What's missing here are results from the stock coil, pretty critical for those considering how the stock coil compares to the Coiltek coil. More later.....

[Don71]

Thanks for the coil tests Steve! I have the 6" smart coil for trashy areas.

I am new to the CTX but I have found that maxing out the sensitivity at 30 gains a lot of depth compared to Auto +3. Using the 6" Smart coil, I get about 6 inches in Auto +3 but 10 inches in Sens 30 on a dime.

-Don

[N7XW]

Thanks for the report Steve.  Although not ideal for nugget hunting, it certainly is interesting seeing how it tests.  I wonder how the results would vary with a completely open pattern with sensitivity  at manual 30, if it can run that high without emi.  I might have to test my ctx on the Bic pen and small lead pieces.

 

[PhaseTech]

I found that Smooth mode helped give a better response on little nuggets, especially targets on the edge of detection. The Relic mode has Smooth by Default.