A
Anonymous
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I can explain this in more technical detail but this is long enough. I don't have the time right now to go into great detail about the circuits that do all this and most of you don't care anyway. I see some question still being posted about null so here goes.
One way to think about the threshold going null is to use a model of a detector that does not have automatic ground balance and tracking.
A detector is ground balanced to pure ferrite, which is the reference for "ground balanced". <span style="background-color:#ffff00;">We are not doing anything to change the electromagnetic field from the transmitter coil.</span> <STRONG>The ground balance is a rejection of pure ferrite so is actually discrimination. </STRONG>There is no pure ferrite in the real world of detecting so that is offset slightly to compensate for the real world of detection.
<span style="background-color:#ffff00;">The primary mineral that has to be rejected is iron oxides.</span> Since a detectors circuits are set for pure ferrite as zero balance any metal will cause the audio to have a positive increase. <STRONG>Iron oxides will cause the threshol audio to have a negative increase. </STRONG><span style="background-color:#ffff00;">This is a way of attempting to explain phase angle so metals all have a positive phase angle and iron oxides a negative phase angle in reference to pure ferrite and the offset.</span>
Circuits in the detector look at the transmitter oscillator for a reference signal to establish the zero to know if a material is ferrite, metals, or iron oxides. The soil is neutral, positive or negative to the reference signal. Iron oxides are always negative so if there are enough in the soil matrix then the soil is negative. A VLF when tuned to a slight threshold with no offset will have the threshold go silent if lowered to soil that is negative or null. If the soil is positive the threshold will increase so we hear a loud sound. If the soil is neutral then nothing or very little change will be heard in the threshold. If the threshold changes, goes null or loud it will stay that way unless the user can do something. That something is to adjust an offset.
It is easy to think of this as a ground balance control and we turn the control and if the signal is negative tune in a positive offset till the detector is ground balanced back to zero. Another way is to say that some iron oxides are such that the detector circuits see a
One way to think about the threshold going null is to use a model of a detector that does not have automatic ground balance and tracking.
A detector is ground balanced to pure ferrite, which is the reference for "ground balanced". <span style="background-color:#ffff00;">We are not doing anything to change the electromagnetic field from the transmitter coil.</span> <STRONG>The ground balance is a rejection of pure ferrite so is actually discrimination. </STRONG>There is no pure ferrite in the real world of detecting so that is offset slightly to compensate for the real world of detection.
<span style="background-color:#ffff00;">The primary mineral that has to be rejected is iron oxides.</span> Since a detectors circuits are set for pure ferrite as zero balance any metal will cause the audio to have a positive increase. <STRONG>Iron oxides will cause the threshol audio to have a negative increase. </STRONG><span style="background-color:#ffff00;">This is a way of attempting to explain phase angle so metals all have a positive phase angle and iron oxides a negative phase angle in reference to pure ferrite and the offset.</span>
Circuits in the detector look at the transmitter oscillator for a reference signal to establish the zero to know if a material is ferrite, metals, or iron oxides. The soil is neutral, positive or negative to the reference signal. Iron oxides are always negative so if there are enough in the soil matrix then the soil is negative. A VLF when tuned to a slight threshold with no offset will have the threshold go silent if lowered to soil that is negative or null. If the soil is positive the threshold will increase so we hear a loud sound. If the soil is neutral then nothing or very little change will be heard in the threshold. If the threshold changes, goes null or loud it will stay that way unless the user can do something. That something is to adjust an offset.
It is easy to think of this as a ground balance control and we turn the control and if the signal is negative tune in a positive offset till the detector is ground balanced back to zero. Another way is to say that some iron oxides are such that the detector circuits see a
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