Modern induction balance (VLF) detectors usually can operate in two basic modes. A true detect everything all metal mode or a discrimination mode. Discrimination modes use various filtering methods to help separate desired targets from the trash. The filtering takes away from overall depth and the target identification gets less reliable with depth. In nearly all cases a detector operating in a pure all metal mode will find targets deeper than a unit running in a discrimination mode.
It is possible to take a detector running in discrimination mode and set it to accept all targets. You are now running with zero discrimination, and the detector now sounds off on all targets. The problem is that some detector manufacturers are labeling this zero discrimination mode as an "all metal" mode since all metals are being detected.
Unfortunately, you have not really turned off the discrimination. A true all metal mode employs no filtering at all, it directly reports a target. In zero discrimination the target is still being filtered, but you are telling the machine to report all filtered targets as good targets. The bad news is you still are losing depth and sensitivity compared to the true all metal modes.
Most metal detectors are made for coin detecting, and so most only run in a discrimination mode. You can set them to accept all targets, to run zero discrimination, but these units simply do not have a true all metal mode. All metal detectors designed with serious prospecting in mind have a true all metal mode. The reason is simple. True all metal nearly always hits hard to find targets, either very deep items or very small, better than detectors running in a discrimination mode, even when set to zero discrimination.
This is so important to me that I will rarely ever consider purchasing a detector that does not have a true all metal mode. Be careful when buying a new detector that if you want a true all metal mode you do not end up with a detector that really is offering only a zero discrimination mode. One clue is that a detector with a true all metal mode will also have a threshold control to set the audio in the all metal mode to a barely perceptible sound level. Zero discrimination modes are usually what is referred to as "silent search" modes without a threshold sound and therefore no threshold control.
It is possible for a detector to run in all metal and discrimination modes at the same time. This is referred to as mixed mode Very cool! I am not sure who first came up with this feature but Nautilus has for a long time offered units that put the all metal signal in one ear of your headphones and the discrimination signal in the other ear. More common are detectors that put the all metal output through the speaker and the discrimination signal on the meter.
The White's MXT has the Relic Mode, which is a mixed mode. I wonder how many people use Relic Mode but really do not understand it. Good targets give a high pitched chirp. Junk targets honk depending on where the discrimination knob is set. But there is a third, more subtle audio that indicates a target is there but the detector cannot identify it because it is too deep. This is the all metal signal. The meter will be blank but there will be an audio signal. When nugget detecting, you want to hear these, and dig down until the target id kicks in. I think many people focus so much on the other two audio responses that they ignore the fainter deep all metal signal. It is easy to fall into a habit of just digging only those high pitch targets. Not good.
White's V3i Mixed Mode program option
The various Fisher F75 and new Gold Bug models have a basic single tone in all metal, but the meter is still active in discrimination mode. So you get the signal, then check the meter. If within range, you will see a target id. If deep, the meter will be blank. It is very similar to the old Compass Gold Scanner Pro, which had a target id meter that functioned while in all metal. The White's V3i has a very powerful programmable stereo mixed mode setting. The DFX also offers mixed mode. The new Garrett AT Gold has a true audio all metal mode while the meter is still working in the discriminate mode.
The same thing can be achieved with many detectors by running in all metal mode and then, after a target is acquired, switching over to discriminate mode to check the target. The obvious downside is that this requires lots of switching back and forth, and a mixed mode detector eliminates the switching.
The key to mixed mode is simple. Those targets in a good location that are so deep you get no indication on the disc channel are the ones you really want to think about. If the area has produced good finds but is now near to being worked out, these deep signals are the ones anyone running in a normal discrimination mode is going to totally miss. Sure, it could be trash. But really deep targets are often the best, and so digging some of these on occasion can produce some really good finds.
I have found from my personal experience that detectors often run smoother and targets are easier to hear in all metal mode. I tend to prefer a detector that has an audio all metal mode coupled with a metered discrimination mode. I just listen for the target, and once I hear it I stop and analyze it with the meter. When in doubt, dig it. Some people prefer to dig only targets that read as probable good targets as they do not like digging junk. I tend to dig anything unless it is almost sure to be junk. In other words, I dig the iffy targets. That means I dig more trash but it also means I make finds others miss. It does depend on how patient I am feeling though, and some days I will just dig those really good targets. Those are getting harder to find these days.
The only place mixed mode does not work well is in very trashy locations, especially the units that generate multiple tones. It just gets real noisy. But for many experienced detectorists mixed mode is a sort of secret weapon. Now you know why!
~ Steve Herschbach
Copyright © 2010 Herschbach Enterprises