Target ID More About Target Size, Than Type Of Metal

[Steve Herschbach]

This post was a response buried deep in a thread on the Equinox Forum, but got long enough on a subject I think about a lot, that it deserved its own thread. Here you go.

I find the whole George Payne way of conceptualizing things to be rather out of date myself. That was back in the day when only one thing mattered - detecting coins. Silver coins in particular. So he was looking at frequency, and most importantly, coin size targets.

If you do that, fix target size, you get the false idea that frequency corresponds to type of metal. Nickels respond here. Gold coins here. Copper coins here. And the biggie, silver coins here. That's how the first coin discriminators were conceived. But it has also lead to this mythology that frequency corresponds to metals. Gold is high frequency, silver low frequency.

No, it's not. There is no correlation between frequency and type of metal if you do not fix the size at some artificial limit. In fact, gold ranges from ground readings all the way to so-called silver readings. If you fix the metal type, frequency corresponds to size. Low frequency big gold, high frequency small gold.

There was also ground to deal with, and ground reacts less well at low frequencies, so a double bonus for silver hunters. You might think it is low frequency working better with silver. But you might also think of it in terms of the detector simply being better able to see the silver, for not seeing the ground.

It's all about conceptualization, and you can conceive of the same thing from different angles. I consider the old George Payne way of looking at things as obsolete from my perspective. It really was only something that worked well in the United States, and only because of an accident in our coin size and metal types. It allowed a scale to be created that worked well with silver coins and nickels, while knocking out a lot of trash items. In most other countries, our target id scale is worthless because their coins do not fit our classic scale.

I detect for gold. I think in different terms entirely. For me frequency does two opposing things. Higher frequency is better for small targets. Small gold, small silver, small copper..... small stuff. But high frequencies also enhance ground, and especially, hot rock responses. The two effects offset each other, and can reverse things if ground is severe enough.

This also totally applies not to nugget hunters like myself, but almost anybody hunting coins and relics under any situation but the classic U.S. silver coin regime. Let me explain.

So I want to find gold nuggets. I must first think about the nugget size that I am looking for. I can look for the more common small gold, or the rarer large gold. If I want tiny gold, I usually want a high frequency detector, the higher the better. Now, here is the kicker. High frequency does just fine on large gold also. In fact, high frequency just detects well on everything - in the air. So air test a Gold Bug 2 on things, and it is amazing.

Unfortunately, the high frequency also "lights up" the ground to an amazing degree, and it is hard to get good depth on anything at very high frequencies. The signal attenuates rapidly in the ground, and the worse the ground is (more magnetite in general), the faster the depth drops off. Hot rocks that never responded at low frequencies are now everywhere at high frequencies.

Lower frequency starts looking better not just because it does better on large targets, but just as much because it is less reactive to the ground.

The 71 kHz Gold Bug 2 is an amazing detector. I can find pinhead gold with it. The big caveat is that in most nugget ground it has low penetration, and is very poor on large nuggets at depth. Not because it air tests poorly on large gold, but because the ground sucks up the signal. 71 kHz is great for small gold, and even large gold in the mildest soils, but in bad ground it has poor depth, and makes hot rocks a real issue.

If I am looking for large gold at depth, I might very well use a lower frequency VLF in the old days, just as much because it is responding less to the ground as anything else, allowing large gold to be more easily found at depth. For my purposes, a PI detector for a long time was just a high power, super low frequency detector. Huge punch on large gold, with minimal ground response. So PI took over early on from the VLF low frequency, large nugget detectors of the time.

I mentioned relic detecting and coins in other countries. If you detect Europe, our U.S. coin scale is garbage. It's not "low frequency = silver." Over there silver can be all over the target id map. Huge silver coins. Or tiny silver coins. Or small coins hammered thin as foil. Or those hammered coins cut to make change. Silver under those circumstances occurs anywhere on your target id scale from ground to the highest reading, 0 to 100. It all just depends on the size, with a little ground effect tossed in to drag things down.

So in Europe, if you want to chase tiny silver cut coins, or very small gold coins, higher frequencies work well, whether it is gold or silver. The metal does not matter. It is size that matters. Relic hunters see the very same thing. High frequencies find the small bits, regardless of what they are - worst fact being tiny ferrous.

I long ago tossed the frequency and metal thing in my garbage can. Here is my reality. High frequency will help me with smaller targets, but also make dealing with the ground harder. Low frequencies simply have less ground and hot rock response, and also less tiny trash stuff response, making them better if I want want to focus on larger targets, like coins or rings.

In my lifetime experience there is a crossover point for gold, and going too high enhances tiny gold nuggets, but also loses depth due to ground issues. A sweet spot develops around 50 kHz, which White's chose ages ago in the Goldmaster II, as being great for small gold nuggets, while still retaining punch in bad ground on larger gold nuggets. Minelab rediscovered this with the Gold Monster, and went with 45 kHz for this very reason. They found pushing high did better on tiny stuff, but the cost in larger heavier gold was not worth it to serious nugget hunters in bad Australian type ground.

If I was hunting tailing piles for ounce type gold nuggets, it is hard to beat a 15 kHz type detector, just like that ancient 15 kHz Garrett Groundhog circuit, that was at the time a high frequency, but in retrospect was a great large nugget lower frequency. The White's MXT at 13 kHz is superb on large nuggets in trashy locations.

If you are in Europe, that 15 kHz sweet spot applied for a long time, but more recently people have discovered the benefits of higher frequencies on these tiny cut silver and small gold coin finds.

Pulse Induction did serve as super low frequency for a long time. You gave up small gold to get big gold as deep as possible. The lack of ground response allows use of extra large coils. It is interesting to me that as newer PI detectors are pushed to get more sensitive to small gold, that ground and hot rocks have also become more problematic. The newest PI nugget hunters suffer from hot rock responses you never saw on the old PI models. PI is getting more like VLF over time.

So Billy, does Minelab put all this in Multi-IQ processing? Of course. But not in the way you think. They think more like me. It's every bit as much about ground, and saltwater, and even EMI, and what you do not want to detect, more so than metal types. A primary choice is saltwater - that forces a low frequency mix simply to avoid the salt response. Which, as I seem to have explained to beach guys a million times, also knocks out small gold responses.

For large coin detecting a lower frequency mix gives clean responses on larger targets like U.S. coins and rings, while getting less ground response, fewer hot rocks, and far less tiny trash signaling. It is not targeting silver coins per se, just larger stuff. For tiny items, gold nuggets, small hammered silver coins, a higher frequency mix works well, but you will deal with more ground and hot rock response, more tiny trash.

Forget metal type. Think size and ground, including saltwater, and hot rocks. As you increase frequency, everything responds better, and small items that respond poorly or not at all at low frequencies will do better. Ground, saltwater, and hot rock signals also increase with frequency. The first cut off is at saltwater. To work there, you must have a lower frequency mix to eliminate salt signal, and you lose all tiny stuff as well, tiny aluminum, tiny gold. This can also do very well on large targets in any ground.

The teens are really nice for general detecting, right on the edge of the salt range. 12 kHz - 15 kHz hits really well on most desired detecting targets, while not being overly sensitive to ground and the tiniest trash targets.

40 - 50 kHz is a sweet spot for gold nuggets and all really small targets, like the smallest cut silver coin, targeting the sub-gram range kind of stuff with some alleviation of ground and hot rock issues that develop at extreme frequencies.

You get up above 50 kHz and you really are just surface skimming for the tiniest bits. Depth just drops off rapidly due to the ground, and so this is specialty range for the smallest targets.

Multifrequency changes none of this, and making a machine that found everything best at all frequencies just gives you a detector that reacts to everything and finds nothing. It is about picking a few divergent frequencies that when differentials are applied, can add extra target information. This is as much about ground as anything else. The classic is the salt beach, where you want to notch out both salt response and ground response. Single frequency can't get you there except in crudest form, eliminating both, while losing a lot of gold. Using two frequencies lets you notch back in some gold jewelry missed by eliminating both ground and salt with a single frequency. 

Looking at two frequencies that are close together is a waste of time and processing power. The target and ground response is the same. But pick two very divergent frequencies, and you will see differences in target response and ground response. This whole idea of having a detector look at and analyze 100 frequencies simply makes no sense, and reveals the nonsense we have been fed for ages about more frequencies being better. Again, there are only a handful of gross frequency ranges that really matter.

Under 10 kHz = find U.S. large coins well, minimal small trash and ground responses, few hot rocks. Call this Park Mode, with a special subset that tunes out salt, called Beach Mode

15 kHz plus or minus, great on a large range of small to large targets, while still not being overly sensitive to ground and very tiny trash. Call this Field Mode. This is an excellent all around compromise mode between low and high.

40 - 50 kHz is great for sub-gram targets, but will make dealing with ground and tiny trash problematic. Let's call this a Gold Mode.

70 - 80 kHz is basically surface skimming for pinheads, max hot rock and tiny trash response. Pinhead Mode?  A niche area for sure.

Four basic options, and really three, since the highest is very niche. It is also comparing results in these three or four options that give you the most bang for the buck in multi. They diverge enough to provide the basis for good differential algorithms.

Again, multifrequency really just adds better ground and target id capability for cleaner, more accurate responses across the board. It's not some magic about finding all targets best at all frequencies by lumping them all together. Most frequency discussions simply miss the reality of what is going on, and what is being achieved by going multifrequency.

I will say it one last time. Think of frequency, whether single frequency, or a mix of frequencies, in terms of the desired target size, offset by the added ground/salt response. Think of the target id scale as a size scale, low numbers are small targets, high numbers large targets. Think less about it being an indication of type of metal. Aluminum responds anywhere on the scale. So does gold, lead, silver, copper. Small foil a low single digit, and aluminum can like a silver quarter. Pick your frequency mix and your target id numbers to match the size of the targets you are seeking, and life will get easier. And quit thinking of multifrequency in terms of finding more targets better the more frequencies you use. Nonsense, just marketing nonsense.

The White’s chart below kind of says it all. I’d certainly be picking a high frequency VLF for the tiny gold. But $20 gold coins? Any good detector is going to work, and I’d be far more likely to go 15 kHz or lower.

Newer Thread in a Similar Vein

 

[Steve Herschbach]

I like this image because it is one of the only ones I have seen that illustrate the effect on size instead of type. Minelab tried to take credit here, but it really was White's that found the 40 - 50 kHz sweet spot for small gold.

Again we have marketing at work. This frequency range is great for many small gold locations, while still doing well on large gold. But it is the gold on site that matters. If the location is old bucket line tailing piles, then there may be no small gold at all. Just larger oversize nuggets, say 1/4 ounce or larger, with main hope a multi ounce nugget. Then this chart is simply wrong, and that 18 kHz detector is now the winner. Conversely, what is there is nothing but 0.1 gram and smaller gold? Not that unusual actually in the goldfields. Now that 71 kHz machine reigns supreme. You have to know enough to read between the lines when it come to marketing, and in this case it is really telling you lower frequency for larger stuff, higher frequency for smaller stuff. Again, does not matter if it is silver, copper, or gold. It's all about size.

[Jim in Idaho]

You're right, as usual, Steve. The frequency thing actually started with flight, and radios. The engineers knew that the laminations in transformers were extremely heavy, and figured out they could get the same performance with much smaller transformers by simply raising the frequency they operated at. The new digital welders take advantage of the same principle, as do the inverter generators.....same results in smaller, lighter packages. Before solid state, the aircraft radios operated at 400hz, rather than the 60 hz of ground-based radios.

Jim

[Steve Herschbach]

I will never forget this guy that visited my Moore Creek gold mine in Alaska, where the goal was finding multi ounce gold nuggets in bad ground. He had a 71 kHz Fisher Gold Bug 2, and I was sporting a 13 kHz Fisher F75.

He swore his Gold Bug 2 could out detect my F75. I told him yeah, on small stuff, but not the large. He said "nope, tested them, the Gold Bug 2 wins." I asked "air test." He nodded.

I knew I had him. So I got a larger nugget, forget exactly what, but 1/4 - 1/2 ounce type thing. We air tested the machines, and sure enough, the Gold Bug 2 blew the F75 away. He was smiling.

Then we buried the nugget at about where I knew the F75 would reach. Decent signal. Gold Bug 2. Nothing. Not a weak signal, no signal. The guy was stunned. Absolutely stunned.

This simple story is why I tend to scoff at air tests. They serve some purpose in showing theoretical depth max info, so if he and I were in Florida on white sand, he would indeed have beat me. Air tests are a nice way to learn target id numbers. But air testing detectors is like testing race cars with wheels jacked off the ground. Dyno tests only tell you so much, what counts is when the rubber meets the road, and with detectors, when coils meet the ground. I habitually hunt bad ground, and not only find air tests of little value, but even results from most detector test gardens, as they are in mild ground. 12" dimes? Are you kidding me? Not even close in my ground. I see often see results half what others see in mild ground. I wonder how many newbies have that happen, watch the internet, and think their detector is defective?

 

[Steve Herschbach]

5 hours ago, Jim in Idaho said:

You're right, as usual, Steve. The frequency thing actually started with flight, and radios. The engineers knew that the laminations in transformers were extremely heavy, and figured out they could get the same performance with much smaller transformers by simply raising the frequency they operated at. The new digital welders take advantage of the same principle, as do the inverter generators.....same results in smaller, lighter packages. Before solid state, the aircraft radios operated at 400hz, rather than the 60 hz of ground-based radios.

You see it very easily with Bluetooth and water. Nice high frequency distance for above water, but you only get inches at best with Bluetooth underwater. I know radio and detectors are different things, detectors are more alternator theory than radio theory, but you see similar issues as regards wavelength and signal propagation.

[Tahts-a-dats-ago]

This thread highlights my reasons for believing this forum is the single best resource available for those of us who wish to learn more about metal detecting, the machines we use, and the science behind it all.

I'm a bit embarrassed to admit that I have been guilty of believing frequency performance pertained to the type of metal buried; that despite the fact that every owner's manual I've read clearly mentions size (of target) when discussing the benefits of various frequencies. For some reason - likely due to my preference for silver coins - I had always locked onto the part that mentioned large silver coins and skipped right over the large part.

Thanks to Steve's ability to explain things in a clear, concise, manner: I am now better informed and (hopefully) better equipped to find the targets that I seek most often.

[Steve Herschbach]

On 1/20/2022 at 9:48 AM, Tahts-a-dats-ago said:

Thanks to Steve's ability to explain things in a clear, concise, manner: I am now better informed and (hopefully) better equipped to find the targets that I seek most often.

Thanks. I hope so. I look at what I write, it's long, a little repetitive, just blah, blah, blah. I don't do more than just type them out, post, and then edit out typos, so it's all very much off the cuff. I just kind of barf them out. But it seems to work, so thanks.

[longbow62]

  Very good topic, and nice easy to understand explanation. Thanks!

[CPT_GhostLight]

Thank you Steve!! Finally the whole frequency thing is put into it's proper perspective. I've been reading so much misinformation about frequencies and multi-frquencies regarding the upcoming new machine releases, especially in some of the other forums.

It took me a while to figure out that frequency was about metal size, not metal composition. Now I'm looking at targets in a different way and it's really helping accerelate my learning. 

So Thank You again for making so much good information available for those that thirst for knowledge!

[King-Of-Bling]

Well thanks for wrapping my head around a telephone pole Steve. All fake news by these marketing gurus on MF ! I have known about some of these things you say just from experience over the years regarding metals and more importantly , the size. Air tests are just that , they give an idea of the readings. What intrigues me the most is the sand , soil conditions regarding all these factors. Such as extreme magnetic black sand and depth. The MF Nox will overload , shut down , won't even work. A PI , isn't much better but does work. Depth is severely compromised on small coin and ring sized targets. The metal doesn't seem to matter much. Large targets don't seem to be a problem , but that's not what I'm after. All these video's guys put out seem to prove their machine , settings , techniques work great in THEIR turf. But definitely not mine. I might have to start calling you DR.STEVE now. Lol