After reading some of the posts this fall about the semi/auto debate I did a little playing around late in the season. I've been a manual sensitivity person for several years. And like with many things you get in the habit of doing thought it might be smart to undo it for a while.
And I'm back to manual.
First- for everyone who hasn't tried this yet. Go outside and find some clean ground away from power lines. Set your sensitivity at 1 manual and sweep a silver dime. Note how far you can lift the coil before you lose the signal. As you start to lose it notice the signal starts breaking up and sounding more like iron. Now switch to Semi-Auto sensitivity. Keep the sensitivity setting at 1. Now see how far you can lift the coil? Much, much more than in manual. Now go back to Manual and start bumping up the sensitivity until you can detect at the same coil height as you were getting at 1 Semi-Auto. I usually get up to 12 or 14.
Now do the same experiment in front of your TV or computer with the power on. Turn up the sensitivity in manual until it becomes unstable. (You might not get it above the single digits). See how far from the coil you can detect that dime. Now go to Semi-Auto. Get the picture? Much more electrical noise in front of your TV and your explorer responded accordingly.
Here are my two cents worth: The main(perhaps almost only) reason to adjust sensitivity is because of ambient electrical noise. If you have too high of a sensitivity in an electrically noisy environment the detector will be responding to noise, sensitivity a little too high and you will get a degraded signal from targets in the ground, way too high and the machine will sound like a possessed pin ball machine and not pick up a target even if it is a millimeter from the coil. Noise canceling can help slightly but for most noise generated by power lines it has little effect. I can usually only see a gain of a notch or two of sensitivity by changing channels.
Auto sensitivity takes care of this problem for you; if it sees too much noise it will lower the sensitivity for you. And that is problem #1; Semi-Auto generally strives for a more stable detector than most experienced users deem necessary, and that can cause you to loose depth.
So Mike, If you can only run 18-20 manual I wouldn't be surprised that in auto it tuned itself down to the single digits, and that is why you lost the targets. You can't run more than 18-20 manual because of the noise from the power lines. I often detect in town and have to run around 12-15 manual in many location. Any higher the detector goes nutty and signal quality decreases.
BUT...
If your test garden was out in the country away from power lines you could crank up the sensitivity up much higher and generally get better depth than you do with your current test garden. You saw signal quality deteriorate at higher manual sensitivities but I'm certain that has to do with where you are and should not be a generalization to decrease sensitivity everywhere.
I don't think ground mineralization have anything to do with where you set sensitivity, the explorer with DD coils will automatically compensate, BUT mineralization will affect the depth at which you are able to detect and correctly ID targets.
I can buy the argument that in high trash environments certain signals will sound better at lower levels because you are not picking every little chunk o' junk.
Problem #2 with Semi-Auto: Adjusting the sensitivity down because of ambient electrical noise is often a good thing, even if it seems to over do it. The problem I see is that the explorer cannot always tell the difference between the noise caused from electrical interference and the noise generated by sweeping your coil over many targets. If you are wading through a ton of trash even in an area away from power lines I believe the detector will detune. But even in high trash there will be less trashy spaces where you would do better at higher sensitivities.
Getting back to the original experiment: I went to one of my favorite sites where I have found many good coins. On part of the site a building had burned down and iron trash and some melted bits of goodies everywhere. I've pulled many coins from between the nails but the signals are getting fewer and farther between.
Anyways, this day I ran the sens up in manual as I usually do, but then before detecting hit the semi/auto button several times without counting so I didn't know what mode I was in. I kept randomly hitting switching modes between targets, (and did switch back over targets). I had a couple of deep hits that I was sure that I would have been in manual, but was surprised to see that I was in Semi. Hmmm. And then I had a couple of times that I had a perfectly solid threshold for several yards. I knew there was more junk than that and sure enough I was in Semi and it had detuned. Turned around and went back over the same area in Manual and got some good hits.
Bottom line is that in Auto you don't know where you are.
Which brings us to problem #3. In auto the detector is supposed to adjust itself to the local conditions. I'm not sure how quickly it responds going from electrical noisy to less noisy or visa versa, or from higher to lesser concentrations of trash. A few times I've had a hit in manual, got in in Semi when I switched over, but after detecting in Semi for a while and going back over the target it was gone; the detector had detuned.
So... I would swear to everyone that manual is the way to go except that GoldDigger and several others run in Semi and detect circles around me.
Chris
