I'll Get Us Started
Well amigo, what say we crank this thread up to a nice respectable level.
Jack
I'll get us started. Here are some notes from The Book of Jack that are some of Jimmy Sierra's thoughts on ground probes, etc. I compiled this stuff from several posts that Jimmy made...mostly on dfxonly.com.
First off, there are 2 ground probes. The one that you enter by pressing ZOOM in Sensitivity on the live control dash board is usually used to give you an idea what the best setting to use on the RX Gain (preamp gain).
Press Menu/TAb to highlight Rx Gain and then hold the coil steady over the ground. You will see the Probe Reading of the Signal to Noise Ratio.
The Signal reading is the % of the signal that is destroyed by the ground minerals or sometimes by electrical interference. The lower this % number the stronger the signal will come through or be received. If this number is 50% or more, you will probably have to reduce the Gain and Sensitivity to operate as this would indicate high mineralization .
The Noise reading measures the External Interference. 0% or a low number indicates very little external noise and low ground interference, thus allowing for using a higher preamp RX Gain. Conversely, a high % reading of Noise of 50% or more would require you to reduce the RX Gain or possibly try to use a different frequency setup on your program or maybe use a smaller search coil.
The bottom line with detecting is always to try to achieve a ratio of High Signal to Low Noise. This is usually done by not cranking up the Gain or Sensitivity so high that you obliterate a good signal with the increase in noise. Too much gain might make the target signal louder, but it cant be heard through the ground Noise. Particularly small and deep targets get the worse treatment. The suggested RX Gain setting is only a suggestion. You may still be able to raise or lower it based on your own observation of whether the detector is operating quietly. It just gives you an idea where to start.
Highlight “Ground Tracking†and pressing Zoom access THE SECOND GROUND PROBE. The probe is on the right. Press Menu/Tab to highlight ZERO and then hold the coil in the air and press Enter. This sets the probe at zero. Now, lower the coil to the ground. This measures the VDI number of the ground, or if you do it over a target, the VDI number of the ground plus the target.
The phase # is just another way of indicating the VDI number. Another way to indicate the mineralization of the ground is the strength of the ground is measured in %....0 to 5% represents weak ground, 5 to 10% could be referred to as moderate ground and anything over 10% I would call bad or heavy ground minerals. If you get a piece of ferrite or some black sand you can test this for yourself. the phase angle in degrees. 0-5 would indicate low or weak ground minerals, 5-10 moderate ground and 10 or more heavy ground mineralization.
By the way, I think I mentioned that in bad ground the 10 High pass filter is probably the best.
Bottom line is that we always end up with the same advice. Whether you have to know all of this is problematic. If you love tweaking it gives you lots to think about. For me. I just run the RX up till I get interference then I back off a bit. Then I try to adjust my AC or Disc Sens up till I get interference and back off. The Disc Sens is where you get the depth. Remember, the RX Gain is really how loud the signal gets, not the sensitivity to the target. You need it high enough to hear a good signal, but not so high as to hear ground interference or outside electrical interference. Then I re-ground balance as often as I need to. Squeezing trigger to enter pinpoint (all metal) and lowering the coil to the ground will allow you to check the ground balance. If you hear no change or preferably a slight increase in threshold, you are OK. If not. Squeeze trigger and press enter and pump a few times and go on with detecting.
Preamp Gain, is actually an audio amplification of the Receive Signal. Yes, you could hear deeper with a higher preamp gain, if the signal was too faint to hear and of course if you have hearing loss, this can help. However, the main function of the Pre amp is to control environmental interference. It is the first line of defense to remove radio, 60 cycle, microwave, power lines etc. from interfering with detection. You see, a higher preamp not only magnifies the loudness of a target but also of noise from environment and from the ground itself.
Another thing, when you pinpoint and you hear a noise when you lift the coil off of the ground it is a sure sign that the detector is not properly ground balanced. This is referred to as lift off and is not good. When this is the case, the coil will go blank as it approaches the ground and in essence is NOT rejecting the ground and will reduce depth and performance.
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