Hi Frank,
Sorry for taking so long to answer you but I have been down in AZ looking for gold nuggets.
Now, I will try to answer your question about the noise I have referred to. First, there is the problem of internal noise. This can be from several sources including the preamp. Normally, the gain isn't high enough for the preamp noise to be a major concern but it does enter the picture when increasing the sensitivity or developing a ground balance circuitry using a later sample and subtraction.
Next, comes the problem of external noise. It is difficult to determine where this noise is coming from but it is there. One strange thing my brother-in-law ran into was the intensity of the noise he noticed when he used his cell phone while he had his detector on. When he used his cell phone, he experienced a very loud and strange warble.
My guess is most of the external noise is from high frequency sources within a nominal distance from the detector. In the field, this could be from transmitting towers nearby or possibly from other devices producing high frequency noises.
One thing about noise that cropped up on my most recent trip to AZ was the lack of low frequency noise I encountered. I joined several other people on an outing and before we left for our destination, I tried to show the two nuggets I had found the day before. Well, I managed to drop the smaller one almost under some power lines.
Anyways, I got my detector out and quickly found the nugget again. BTW, I was really surprised at the small size of this nugget. When I got back home I weighed the nugget using a powder scale and it came in at just over 1 grain. I would have never believed the PI would find something that small, but it did. I suspect the ability of the PI to detect this small of a nugget was because of both the shape and the purity of the nugget itself, as well as the short delay I was using.
Getting back to the noise situation, I found I had almost no noise as the result of the nearby power lines, indicating that low frequency noise isn't the problem. Rather, noise problems appear to be more of a function of much higher frequency origon. In fact, I could operate right under the power lines at the location where I dropped the nugget and other locations without any negative results.
I would like to point out that while I was out in the field, away from most typical noise sources such as those found in town such as computers, TV's, etc, I encountered almost no noise problems at all. In fact, the noise problem became almost a non-issue, except for a very slight noise level because of my increased sensitivity.
I know I haven't really answered your question specifically, but this is the best I can do at this time. The noises I experience during my testing at home and close to houses and associated noise sources is nothing like I have experienced in the field. Again, in the field, away from civilization, the noise problem is almost eliminated. At least, it is on my detector. At home, the noise level varies from day to day and even minute to minute.
Reg
