Noise Cancel and Digital Readings

[Anonymous]

Glenn and All, here is one that may be of interest. I tested the old quarter I have had in the ground for years with different noise cancel channels. The digital readings and crosshairs change locations and numbers depending on the channel. The best and highest reading were obtained when I used the channel selected by Auto Noise Cancel. The conductivity would vary from as low as 23 to a high of 29, 28. Ferrous reading would vary from 00 to 2 with 0/29 being the best at the channel selected by Audio Noise Cancel which was channel 5. I was wondering why the readings would be different from one user to the other on the same targets and this may account for some of that.
The bottom line to me is the importance of noise cancel at different sites or if there is external EMI. I also used noise cancel right over iron and a coin to see if this would cause a different channel to be selected and it did. A noise cancel over iron caused channel 10 to be selected and over a coin moved the channel from 5 to 4. I am not sure what all this means but will think about this for a while.
HH, Cody

 

[Anonymous]

Cody,
GENERAL
It is my opinion that the Explorer II uses a correlation detection process. With your technical background you are probably familiar with the theory behind this.
The basics of the correlation process can be found in any book that explains the Fourier analysis (how a periodic function can be broken into a DC component plus a fundamental frequency and its harmonics.
THE ADVANTAGE OF TIME DOMAIN ANALYSIS
The time domain analysis of the detection signal will essentially eliminate any portion of the signal that is not equal to or a harmonic of the transmitted fundament signal from the coil.
THE EFFECTS OF EXTERNAL NOISE ON THE DETECTED SIGNAL
If the external noise is below the sensitivity threshold, then a target ID <span style="background-color:#ffff00;">WILL NOT </span>be given to the hunter.
But, when the combination of the external noise plus a target signal is above the sensitivity threshold, then a target ID <span style="background-color:#ffff00;">WILL</span> be given. In this case the external noise component will effect the composit signal and result in some degree of error in the target ID. The degree of error will depend upon how closely the noise frequency components are to the transmitted frequency spectrum.
Therefore, some channels will be more susceptible to errors than others. The noise cancel process should select a channel such that the external noise produces the least effect of the target ID.
THIS OPENS MY EYES TO THE NEED OF THE NOISE CANCEL OPERATION
Before reading your post, I would only noise cancel if I heard noise in the headphones. But, now I realize that just because you do not hear any noise in the headphones does not mean there is no significant noise present.
Hope this helps. HH,
Glenn

 

[Anonymous]

Thanks, I understand and appreciate your expertise in these areas. It takes a little longer for me to think it through so this saves a lot of time and mental energy. I also became more aware of why we need to noise cancel even if we cannot hear noise. I also was under the impression it was when we hear noise that we cancel.
Again, appreciate the explanation.
HH, Cody

 

[Anonymous]

One question. If we do noise cancel in presence of even small piece of metal under the coil eddy currents will produce noise and channel will be wrong. Never know for sure if any trash or hot rocks under the coil so it may be correct to make noise cancell at about 20'' over the ground to minimise the relation?
HH
Dok-Atn

 

[Anonymous]

Noise cancel should be done with the coil flat on the soil with no motion where there are no targets in the soil as you know. If the coil is in the air then it acts more like an antenna to pick up stray RF something like not being grounded. If you lift the coil and listen and turn in all directions you can find the location of EMI. They indicated in the Owner's Manual to noise cancel with the coil flat on the ground with no motion as the coil responds differently to EMI in this position than when the coil if off the ground.
HH, Cody

 

[Anonymous]

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