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[Captain Kirk]

Cody,

I do not know that much about the details of the Explorer design. I just ask myself the question about the purpose of the null. To me it makes sense that the null is just the detectors means of letting the user know that a rejected target has been detected. The opposite approach would be to not inform the user at all by leaving the threshold tone undisturbed. But, it seems that it is useful to inform the user that there are targets there that are being rejected.

The next issue is what should determine the length of the null. In looking for an answer to this question we must make a determination as to how long the target ID should last. Supose that you are sweeping at 5 feet per second (I know that is very fast for the Explorer). That suggests that the center strip is over the target for only about 1/60 of a second or 16.7mS. That is clearly not enought time to sound the target ID tone. Therefore, the tone must be stretched out to some degree. Also consider that the detector electronics would like to be able to look at multiple cycles of the received signal in order to make a more accurate target ID. All of these factors are probably what determines the length of the null time. When we switch to FAST on, then the Explorer probably shortens the process down to some degree at the expense of accuracy.

If the only purpose of the null is to inform the user of a rejected target, then I see no reason why the null should not last as long as the target ID falls into the rejected target region or at least some minimum time. As soon as the detector determines that the target no longer falls into the null region, then the null should terminate essentially immediately. I see no reason why the null duration should be effected by the strength of the signal as long as the combined signal (of a good target in close proximity to a rejected target) is greater than the threshold setting.

But, of course I may be out in left field in all of this.

HH,
Glenn

 

[Cody]

I follow your thinking and agree. The null is just to let the user know something has been rejected. The other side of the delay is how long a tone is sounded. Glenn, at 3.5khz to 100khz the target appears to not be moving in relationship to the mechanical sweep speed. I think I read that in the patents and would not have given that much thought on my own.

I know a major difference in the Explorer is the coil is directed coupled to the preamplifier. No capacitors to mess with. The length of the sound or null would take into consideration the filtering. I have guessed that Audio1, 2, 3, is how the audio is filtered. They indicated that Auido1 has better target ID and it is clearly delayed for a longer look at the target sample.

 

[Cody]

Yea, I know you are right. I have found some nice coins that way. If I don't get brain overload in heavy trash I do OK with that.

 

[Captain Kirk]

Cody,

I do not know what is meant by "the serial or parallel analogy" means.

Regarding the shape and orientation of a target:
If the detector works on the basis of the distortion of the magnetic field, then I think that we can say the following.

#1 The eddy current always flows perpendicular to the magnetic field.

#2 The greater the cross section of the target that is presented perpendicular to the magnetic field, then the greater the distortion of the field. This statement may come under question as the shape of the target becomes very irregular, e.g. a smaller cross sectional area but very long in the direction perpendictular to the cross sectional area.

#3 A nail that is in a plane parallel to the coil will distort the field much more than one that is perpendicular to the coil plane. For example, a nail on end does not provide much of a target cross section area.

#4 A nail that is laying north and south will produce a much greater distortion when the center of the coil is running north and south, but will be seen for a much shorter time duration than for a nail running east and west.

#5 A nail that is laying east and west will produce a weaker signal when the center of the coil is running north and south, but it will have a much greater time duration than for a nail running north and south.

HH,
Glenn

 

[Captain Kirk]

Cody,

The receiver coil does not have to be capacitively coupled because you can not develop any DC voltage across a coil winding.

HH,
Glenn

 

[cdog46]

Poor Buffalo Bill-has ever gotten the flack on this one! One thing I do know-Buffalo Bill-you have tremendous knowlege in general and have been aterrific contributor to these forums.

So what Upstate Jim? He probably is THE expert on EX1's and 2's. He is a tremendous individual not only for his knowlege and breathe of knowlege-but also his willingness to answer new peoples questions. I also think he is the biggest walking advertisement for Minelab explorers in terms of his finds.

Upstate Jim's neighbor Upstate Charle's has got it right on this one also in terms of having Buffalo Bill having to dig 1000 or two coins with the Ex2.

So what do I know compared to the above? In addition to being a smart ass-I have 37 years detecting experience and have had or have an EZ 1& 2, cz7, cz3d, whites xlt etc and I agree wiyh Upstate Jim. Buffalo Bill I believe was a EE-I'm just a lowly senior electronic tech and lawyer but this much I do know-Upstate Jim wins on this one.

Buffalo Bill-metal detecting is very much like electronics (high frequency RF in particular-my branch) it never stops doing strange things & you never stop learning especially the more capable the machine is.

 

[Dave Z]

What I do with the DFX is set the sweep speed at 1,filters at 4 and recovery speed between 22-30.Sweep slowly and listen for any positive beeps.If the the spot is a good one.I'll go back over it with the small coil.I think the problem your having IS rejecting the iron.If a good target is lying next to iron and you're rejecting the iron.Your detector will still be nulling the iron as you sweep over the coin.I think this is the problem your having.Where I hunt,I look for the iron,cuz where there's iron,there's been people.Dave