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Date Posted: 16:52:05 08/22/02 Thu
Author: Reg
Subject: Re: Geez.....
In reply to: Phil(NM0 's message, "Geez....." on 14:13:57 08/22/02 Thu

Hi Phil,

I suspect you air tested the two detectors to come up with your results indicating the Infinium would or could exceed the SD in depth.

Unfortunately, PI's in general are very temperamental about air tests. SD's are extremely temperamental in this regard, much more so than other PI's I have tested. I am not sure why, but I have found them to be much more suseptible to noise in general, and especially if the coil is raised above the ground.

I realize most people use the standard air test to compare detectors, but it isn't a good test, especially when trying to find out what will happen with a PI.

PI's by their nature require a special "front end" circuit that is very broadband. As such, it will easily pick up any external noise, which can easily create havoc with testing. What is worse is the noise may not be that noticeable but it can significantly reduce the depth of detection.

Example, I can experiment with a 5 grain nugget and have the air test change as much as 2 to 3 inches in detection range, just because of the external noise. Because of some noise reduction circuitry I have installed in my PI, the noise level doesn't appear to change that much either. I have to look at the noise level with my scope to see what is really going on.

Strange as it may seem, I have found PI's to be direction sensitive at times also. By this I mean I might be able to detect an object when passing over it swinging the coil north to south and visa versa, and not be able to detect the same object when swinging east to west.

What is really strange is a PI might be a little more sensitive in one direction than another. Example, you might hear a little stronger signal, say when the coil is passing east to west than you can hear when the coil passes back over the same object from the opposite direction. This will be more noticeable when the object is lying on the ground.

I have experienced similar situations with a VLF, but been able to attribute it other conditions. The PI is much more sensitive to this condition. Due to the broadband preamp, the PI is much more sensitive to earth field effects as well as the motion effects of the coil over ground. Any slight imbalance in the compensation circuitry can amplify this problem.

Like I said in my post a little earlier, it is extremely difficult to compare a VLF and a PI. Just as important to know, is the testing normally done with a VLF may not work that well with a PI.

Reg

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