sensitivity verses depth

[urchin]

I know this has been hashed out somewhere in this forum but I watched a video where Kevin Hoagland said sensitivity has nothing to do with depth and more to do with stability. He said that the sensitivity is about the signal coming back from the ground and has nothing to do with ground penetration.......is this correct??

 

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[beep1971]

I'm no electronics expert, but the basic way i understand it is that the signal from the coil is where the raw depth is, eg my machine has 3 levels, it's down to how much filtering of the received signal has been programmed into the unit. The sensitivity setting is just that, it that regulates how much of the received signal it lets through processing, the higher it's set the more weaker signals and ground you hear and you start to get false signals etc. audio gain boosts the weak audio signals.
Take the difference between the ATMax running all metal vs disc channel, the disc channel has more filtering which equals less depth.

 

[Tom_in_CA]

.... sensitivity has nothing to do with depth and more to do with stability. He said that the sensitivity is about the signal coming back from the ground and has nothing to do with ground penetration.......is this correct??

This is confusing some "which came first, chicken or egg?" type question. The sensitivity setting DOES INDEED have much to do with depth. However, yes.... you run the risk of loosing stability, when you increase the sens. too much for the type ground you're in.

Thus the two terms need not be exclusive of each other. Yes sensitivity has to do with depth, but yes sensitivity has to do with stability AS WELL. Both statements are true and are not exclusive of each other.

I recall that My Spectrum and Whites Eagle SL II had a signal return knob which operated in conjunction with the sens. setting. I recall being told that the sens. knob was the "send" signal, and the signal return knob was the "receive" signal. Or something to that effect. All other machines I've used simply have the sens. knob.

 

[Terry Soloman]

Bill Southern, an original Arizona nugget shooting legend, once explained "gain" or, sensitivity, to me like this. You have to think of gain (sensitivity) like the old "squelch" dial on your CB radio. On some rainy days you had to add in a lot of squelch to remove the static from your reception. But if you added too much, you went to all static and couldn't hear anything.

Gain or Sensitivity works the same way. In Neutral soils you can crank your sensitivity to max most of the time with good results (depth). However, if the soil is moderately mineralized, you may actually lose depth by maxing out your gain.

So called “Super Tuning” is really just a load of crap. Try super tuning in red soils or black sand situations. On a good metal detector, the controls and settings work TOGETHER. Ground balance and sensitivity MUST be in tune and working together for the best depth.

 

[beep1971]

Gain and sensitivity are 2 different functions.

 

[IDXMonster]

Ok,I’ll bite.
The only thing that the operator has control over that will dictate depth is size of coil.
On ALL machines except the Deus and a couple others,the Transmit signal is FIXED. It is what it is.
Turning UP your Sensitivity let’s you hear more of what is already within the coils field. Because the strength of the field tends to weaken at the perimeter,turning up the Sensitivity gives the IMPRESSION you are gaining depth,while you are really just hearing more of what is in the weaker,outer part of the coils field.
Gain is post signal processing,meaning...the machine has to have received the signal already. The Gain will AMPLIFY a signal that has already been picked up via the amount of a Sensitivity applied.
This is why it is suggested that the LAST thing you do to mitigate EMI or a lot of false signals is to turn down your Sensitivity. While it may be practical in heavy mineralization or heavy trash to turn Sensitivity down in order to hear more of the true, clear targets you’re after,you will lose operational depth.

 

[urchin]

Thanks everyone, I think I have a better understanding of sensitivity now.

 

[beep1971]

My machine has 3 levels of TX power, it does give more depth, but the circumstances need to be right.
On milder ground it rocks, with high or low freq and different coil sizes it's no problem, even with a small coil the depths can be outstanding, in boost mode it air tests silly, like14"-15" on a silver dime in disc with a sniper coil, so if your soil is real mild you can reap the rewards.
On more mineralised soil it favours the lower freqs. Using high freqs and it will overload just by looking at the ground lol but it gives you a heck of a versatile machine.
As IDX mentioned, the Deus has a TX power setting, it's alot milder and of little benefit to myself. The GM5+ has it also, and i found it a little more powerful than the Deus setting, but it's a more basic machine.
Obviously with a manual GB detector you can gain a bit of depth by letting more of the ground zone through, but you will also dig a bit more iron.