Noise Cancel and Sensitivity

[Cody]

Noise Cancel and Semi-auto sensitivity are important to understand. If we test our detector in semi-auto close to EMI we see a considerable decrease in sensitivity. As an example in my home I have a shop where I rebuild and repair antique guitars and amplifiers. I have florescent lights which will really tear up the audio in some amplifiers; Fenders are really bad about this, and the Explorer. I can only detect a coin at about 7

 

[Chris(SoCenWI)]

Cody,

Your findings mirror mine exactly, in Auto mode it doesn't matter too much where you set the sensitivity: The explorer will greatly adjust the actual sensitivity from the set point. If you are at 1 in Auto it may bump it up to the equivalent of manual 16 or higher. Conversely if you are running at 32 Auto it may back it down to 16 or less. It is kind of like adjusting a potentiometer with a loose set screw.

The Problem as I see it is that the explorer cannot differentiate between noise from EMI and the noise from sweeping the coil over ground that contains many targets. The explorer in both cases thinks this is noise and backs off the sensitivity greatly to try gain a stable thresh hold.

Most of the more experienced users believe that the explorer will back off too much in Auto mode. I am absolutely convinced that in most situations higher manual sensitivity will give you more depth. I spent most of last summer detecting the terraces near my house where they were doing road construction. There are power lines everywhere and I could seldom run above 17 in manual. I'm sure if I was running in Auto it would have detuned even farther. The first few passes I found some silver halves and other coins. As they removed dirt I started to find older coins. I have hunted many other sites without EMI where I could crank up the sensitivity and would have been able to get the older coins at these depths, but could not here because of having to run at low sensitivities.

There are a few times when I have gotten better signals on a target at lesser sensitivities, but this is the exception and not the rule.

My experience with noise cancel is that it doesn't do much with noise from power lines. You may gain a click or two after a noise cancel, but often the converse is true. It CAN be very effective on noise from a less broadband source.

One further note.. I've come across people using explorers that were complaining they could not get any depth. They had most of the screen blacked out- a learned program- and had the sensitivity cranked up too high. Opening up the screen revealed that the machine was highly unstable but they could not hear it because of all the discrimination. The moral of the story is that if you try to run at the cusp of stability you need to be able to hear if the explorer is going nutty and this requires minimal discrimination.

Chris

 

[Cody]

Good post and I am not sure on the EMI and "ground noise". I can tell the difference by using Edit and Accept so assume the detector's electronics has EMI in one group and then all other noise in "ground noise". I am slowly working my way through this and add comments such as yours to my thinking and looking at the patents.

They are listed on the Geotec site and I go there as it is easy to look them up instead of digging through the patents at the US Patent site. Look in the Owners Manual towards the back and it list three patents of which one is for the coil.

Anyhow, good post and informative,

 

[Cody]

I have been thinking about this and I am fairly sure what the semi-auto is designed to do but have enough hesitation and think I can use the detector good enough that I have also gone to manual sensitivity. I do think a new user is going to be a lot happier with Semi-auto at the machine really runs smooth. What I don't understand is the conversations I have had with Minelab and they absolutely insist we will do better with Semi-auto and be more effective. That sure is in line with what I think as far as "theory" is concerned. I am going to go back and try both again and see if EMI at the sites I hunt really make a difference. My thoughts was noise cancel takes care of that and sensitivity takes care of the ground noise. Anyhow, again you are posting some important information in that is it is what happened in the field that really counts.