Those impressive video results of the Fisher Impulse AQ with its 12.5” mono coil on the 10K Gold ring at 17”-18” and 14K Gold ring at 19”-20” as did a 22K Gold ring drove my curiousity to air test two Gold rings using a QED in its Beach Mode-11 operating at its pulse delay of 7.5uS with a NF 12” Advantage mono coil.
For my test, the QED’s settings were Threshold-B at 5 below Null and Factory Default for Threshold-A at 30 and Gain at 1.
(Threshold-A settings range from a 1 up to 90 and the Gain settings range from 1 up to 10}
The results for a clear response on a 3.04-gram 9K 21mm diameter Gold ring was 17” and on a 2.05-gram 18K 19mm diameter Gold ring was 16”.
I have no idea how a QED using its Beach Mode would operate within a Beach environment and my intention is not to compare in anyway the QED to the Fisher Impulse AQ only results using a pulse delay of 7.5uS.
I had a guy approach me at the lake today who lost a 14K college class ring size 11. I told him I would spend time looking for it and get it back to him if I happen to recover it. I have a 10K college class ring I found this year(unable to locate owner) but, it's a 10K. On the Simplex, it reads 64-65, the Nox hits at 20-21 I'm wondering how much of a difference the 14K will read. Any help would be appreciated. Thanks.
By ☠ Cipher
What do you make of this description on KellyCo? It seems to suggest the IPTU sensor would work with machines other than the Invenio. Does anyone know if that is true and how that would work?
"One of the biggest issues that people run into when metal detecting is difficulty with accuracy. The IPTU Sensor (Invenio) is going to help increase your accuracy and help you find more items and be sure what they are and where they are better. This is an easy to install sensor and is going to make a world of difference when it comes to your overall success when metal detecting. This sensor works with Invenio detectors and is a great addition to any metal detector."
By Steve Herschbach
The original 1985 Fisher Impulse metal detector
A note on saltwater. On dry land and in freshwater pulse induction (PI) detectors can be run to max limits. Not so in saltwater. There is an inherent limiting factor in saltwater that tends to flatten top end performance on all PI detectors, or even VLF detectors for that matter. The problem is simple - saltwater is conductive and so is visible to electromagnetic devices like metal detectors.
Pulse induction detectors saw their earliest use as beach detectors because of the pulse delay control. Lower pulse delays expose items with a shorter time constant, and this usually means low conductive and/or small items. As the pulse delay increases a PI loses overall sensitivity. Early beach PI detectors all came with a preset, relatively high pulse delay that made saltwater invisible to the detector.
In general somewhere around a pulse delay of 10 uS saltwater becomes visible to a PI detector. The number varies for several reasons, First, salinity varies greatly around the world, everything from salt free fresh water, all the way to the Great Salt Lake, which is water supersaturated with salt. Oceans and bays vary, and especially bays that have large river inflows, and therefore lower salinity levels. Large, shallow, enclosed bays with no rivers may act as evaporation dishes, and have abnormally high salinity levels. Further, this effect is accentuated the deeper you take a detector, and so detectors used for true SCUBA diving must be run at higher delay levels at depth. You can't just pick a number like 10 uS and say that is the magic number for dealing with saltwater. 9 uS may work well, or it may take 12 uS to eliminate feedback from the saltwater in your location.
The coil detects like a globe in all directions, and so it is not just the water under the coil, but all around the coil that is affecting it. This large ball of saltwater is like a giant target. Many hunters riding the edge of sensitivity can tell you a detector can pick up waves as they pass over, making the water deeper.
This long winded explanation is to make people realize that you can't just magically make the detector itself more powerful and get "more depth" or "more sensitivity." The salt range overlaps the tiny gold range, and so if you make a detector able to detect fine gold chains and tiny gold ear rings, it will detect the saltwater. If your set the pulse delay to eliminate the salt signal, you lose the tiny gold items. This is an inherent wall on both PI and VLF small gold performance in saltwater. We have had detectors for decades that can detect tiny gold that people say they want to detect in saltwater, the Fisher Gold Bug 2 for instance. The problem is the Gold Bug 2 will not work in a saltwater environment. The water is just a huge signal to a Gold Bug 2. I have gone round and round with people for the last twenty years trying to explain why you can't detect certain fine gold chains, small ear rings, small platinum, etc. in saltwater. The problem is not the detectors - it is the saltwater.
The same problem exists to some degree on trying to detect larger items. You can make a very powerful detector, but you have to inhibit the detection of saltwater, and this tends to put a ceiling on the maximum attainable performance in saltwater. No matter the machine you use, once you hit the saltwater you can only advance the pulse delay and sensitivity controls to a certain point before the detector starts to protest. The exact settings where this occurs will vary by location. This all assumes "no mineral" sand. Add magnetic soil content to the beach or bottom being hunted, and you have yet another limiting factor to contend with.
Add this all up and do not expect to run the Impulse AQ Limited at a pulse delay of 7 Us and maximum sensitivity in a typical saltwater environment. You will likely have to lower one or the other or both settings to get stable performance, and this requirement tends to be a limiting factor on all PI performance in saltwater. It is this knowledge that keeps me from ever expecting miracles to occur when I try new detectors in saltwater environment. The problem is not the detectors - it is the saltwater.
The original 1985 Fisher Impulse metal detector
By Steve Herschbach
I have seen it said a few times now that the new Fisher Impulse AQ has "no holes". This started as a very specific mention on the part of the designer, and now has been expanded into a range of assumptions that do not match how I view the subject.
First, what is a "hole?" The classic definition originated around ground balancing pulse induction metal detectors. The first and most simple ground balance method is a basic subtraction. Determine where the ground is reading with the detector, then provide a control to subtract that signal.
Many people do not realize that ground signals and gold nugget signals within normal range are basically infinite and overlap 100%. This is due to the nature of natural gold nuggets, which occur in endless variety as far as size, shape, and composition. When added to the ground, they mix and blend with the ground signal, and in one way can be considered a naturally occurring component of a ground signal.
There is one simple rule you must keep in mind that makes all discussions of a "hole" simple. For every potential ground signal that exists, there is also a corresponding gold signal.
The ground balance control is just a special discrimination control. When you eliminate any one type of ground signal or hot rock, you automatically eliminate any gold signals that are identical to those ground and hot rock signals.
The nature of the electronics involved is not 100% in that the ground balance rejection point is not perfectly sharp edged, but covers a small range. Within this rejected ground range, you have the most intense rejection effect at the setting itself. However, items that fall close to the setting, while not eliminated, are weakened, and deliver less than normal depth. The effect is similar to that seen when black holes are diagrammed, and targets that are unintentionally eliminated because they fall into this range are said to "fall into the hole."
The classic metal detector ground balance "hole"
This can also be seen with many VLF detectors. Take a detector with a manual ground balance control, and grab a coin. Air test the coin depth, while running the ground balance control to both extremes. Depending on the coin or target you test, like a gold ring, you will usually find that the depth varies with the ground balance setting.
On a simple ground balance detector with a single ground balance "channel" the effect is quite pronounced. On the White's TDI the ground balance setting is normally around 8. This also corresponds with nuggets weighing approximately 1/4 ounce, though again, because of the natural variation of gold nuggets, the range is actually very large, and based on the time constant of the nugget, not any particular weight. Any nugget that reads at the setting of 8 is essentially eliminated. Nuggets that fall near to the setting have greatly weakened responses.
Minelab first addressed this issue with detectors that have two ground balance "channels". Channels have historically referred to detectors that have two separate ground balance "channels" but people are now misusing the term to refer to detectors that are returning dual audio results that can be separated into "channels." This is not the same thing. A dual channel PI has two ground balance sample points that are being compared. The Minelab SD 2100 has a switch that lets one chose one or the other or both ground balance channels. One favors long time constant targets (large nuggets) and the other short time constant targets (small nuggets). The ground result is roughly the same on either channel. By comparing and combining results from the two channels, emphasizing the one with the strongest nugget signal, the "hole" is largely eliminated. This was the major advance and secret to Minelab PI MPS "multi-period sensing" detector technology. The "timings" developed over time were progressively sophisticated comparisons of multiple channel results intended to address specific ground and hot rock situations.
No matter what though, the hole never goes away entirely. If you eliminate a certain hot rock, you lose gold that reads like that hot rock. People who set for and are willing to dig what others consider ground and hot rock noises, find targets with PI detectors that others miss. It's one of the secrets of the pros. At a minimum, on Minelab detectors, hunting with a different timing will reveal gold missed with another timing.
To sum up, a hole in metal detector terms is what occurs when a good item is unintentionally rejected when some undesired item is rejected or discriminated. This usually refers to good items lost due to the ground balance setting, but can include any items accidentally rejected due to a detector eliminating some undesired target or range of targets.
And that brings us to the new Fisher Impulse AQ and the claim of "no holes." As in all marketing claims, yes.... and no.
Alexandre Tartar has be quite firm since day one in emphasizing that the AQ is specifically designed to find gold ring range targets to the exclusion of everything else. In his early writings he says that the AQ does focus on this range, and that in that defined gold ring range there are no holes. This is true.
Unfortunately that statement has been extrapolated beyond the original intent. It all depends on how you want to define things. I am going with the definition above "a hole in metal detector terms is what occurs when a good item is unintentionally rejected when some undesired item is rejected or discriminated."
Under that definition the Impulse AQ has two holes. They have simply been redefined as not being holes, but being something else. The ground balance control has been hijacked on the AQ and is employed as a discrimination control. Instead of being set to reject a certain ground signal, it is being used to reject a certain target range, specifically many ferrous targets. In the process, most U.S. coins except nickels are also rejected. So we have called the ground balance a disc control, and are attempting to eliminate ferrous items. The unintentional side effect is that many high conductors including most U.S. coins are rejected. Note that if this setting is high enough, heavy large gold rings can be eliminated. The ground balance hole is there, and in a big way. We are going to define it out of existence however by calling it a discrimination control.
The Volcanic Mode, by eliminating intense beach mineralization, will have an adverse effect on most targets. It has to. You can't eliminate a ground signal that severe without an unintended adverse effect.
The Impulse AQ is also locked into salt rejection mode at all times, even in "all metal" mode. Well, almost all metal mode - I wish there was a switch to shut off the salt rejection. There is still a filter engaged, so this is not a pure pulse mode. The machine is always set to eliminate salt signal. This means that small gold items like thin gold chains, small ear rings, aluminum foil, and small gold nuggets, are also going to be unintentionally eliminated. You catching the drift here? Unintended side effects, trade offs deemed necessary to get a desired end deemed more important. Welcome to metal detecting. So we have another hole in the extreme low end, but we have redefined it as being a preset salt rejection mode.
So does the Fisher Impulse AQ have "holes" in the detection pattern? It simply depends how you want to look at it. If you define the only genuine desired range of the detector as being a narrow range focused on gold rings, there are indeed no holes in that particular range. But if you consider the entire range of possible targets that can be found with a metal detector, the AQ is explicitly said to reject at least two target ranges of concern to some detectorists depending on the settings. It always is in salt rejection mode, and so will always miss low conductor targets. Engaging the disc mode will also lose many targets of interest to coin hunters.
So are those holes or are they not? You decide. Fisher does not define the term anywhere to my knowledge. It can mean whatever they want it to mean. Leaving it undefined means people just plug in their own assumptions. Frankly, none of this should come as a shock or a surprise to people who have been paying attention. I in fact have already written a long article, the Fisher Impulse AQ Discrimination Explanation, that has put all this out there for anyone with ears to listen. I have concerns that the marketing folks seize on simple catchword phrases, that make nice blurbs for people who don't really understand the technology and the limitations. People read what they want into such statements, and this in turn creates unrealistic expectations. This inevitably blows back when disappointed customers feel they were mislead. Frankly, I have always believed in underselling a product and letting it prove itself. Setting up unrealistic expectations is a setup for failure in my opinion. Keeping expectations realistic results in pleasant surprises and better long term outcomes. My goal here is therefore not to knock the Impulse AQ, but to educate people into having realistic expectations. Will you buy this detector and just go dig rings while digging no junk? No, that is not going to happen. Read the article at the link above. Are there items that the AQ will not detect as an unintentional side effect of eliminating undesired signals. Absolutely.
Finally, let's talk the upcoming Fisher Impulse Gold model. The Impulse AQ fails as a gold prospecting detector because the ground balance control is being employed as a discrimination control, and because the detector is locked in salt rejection mode. Obviously the salt rejection needs an ability to be turned off. I'd prefer this as a control so salt mode can be engaged on salt alkali ground in the desert, or for some hot rock rejection. It would be a shame to eliminate it entirely, but that may be their solution. If we had a switch for that on the AQ it would have been nice also for dry beach and fresh water use. In any event, salt rejection must be gone or optional on the Impulse Gold, or all that small gold the machine is designed to find is lost.
The disc control has to go back to being a ground balance control. Discrimination capability outside of perhaps a dual tone effect common on ground balancing PI detectors will therefore be unlikely on the Impulse Gold. What also will happen with an adjustable ground balance will be the inevitable hole that follows with such a control, Fisher can minimize the hole as much as possible, but again, you can't reject a certain hot rock without losing the nugget that has the exact same time constant.
The ultimate constraint on the kind of gold a PI detector can find has never been pulse delay. There are commercial PI detectors designed to find pin-sized targets. For gold prospecting the constraint is always the ground. If you make a detector with a 1 uS pulse delay, all it will do is light up the ground like the largest target ever found. The key is the ground balance technology employed, and how efficient it is at eliminating ground and hot rocks, plus alkali effects in some areas, while losing as few gold nuggets as possible.
There is a point where making the pulse delay short enough basically duplicates what a high frequency VLF does, and it creates all the same problems with ground and hot rocks you get with a high frequency VLF. Short pulse delays and air testing is totally meaningless. The Impulse Gold will have to ground balance effectively, and doing that will bring its performance parameters into line at best, in my opinion, with the limits we have already seen explored for those who are familiar with and have used current available technology. The main low hanging fruit waiting to be picked here is high performance in a light weight, ergonomic, and affordable package. Anyone expecting massive improvements in existing gold prospecting technology probably does not understand the constraints involved, and is likely to be disappointed. My advice? Be realistic and look for a new benchmark for what a gold prospecting detector can do without breaking your wallet or your back, and you are going to be happy with the new Fisher Impulse Gold.
That is how all this works folks, time constants. PI detectors know nothing about ground or gold or ferrous or non-ferrous. Conductivity is loosely involved if at all. You can accept targets and reject targets or ground based on their time constant, and for every good target there is a bad target that has an identical time constant, and vice versa. That is the reality of the technology, and getting your head around it is the key to knowing what these detectors can and cannot do. Does the Impulse AQ exhibit any detection “holes?” My answer is define first exactly what you mean when using the term, then apply that to the AQ to get your own answer.
UNDERSTANDING THE PI METAL DETECTOR by Reg Sniff
For anyone who wants to dispute any of the above, please provide an exact definition of what a “detection hole” is, and how it does or does not apply to the Fisher Impulse AQ.