Hi Morgan
In the size of my possibilities I'll respond your questions:
1. No.
2. There are severals. a) I/B metal detector as pistol, very precisse but "slow". b) Oscillator (no search coil) in combination with antenna wich mix input with the reference (the oscillator). c) Infrared.
3. Yes you can detect a coin at distance but not a car at 15 m, because with electronic LRL you detect the "emission" of the phenomenom. Of course, you can detect a car at 15 m with magnetometer.
Important parameter are the environmental conditions.
I design a pistol 10 years ago wich results in an interesting instrument. This show environmental activity in uamp, but only buried conductive metals umbalance it. Collateral discovery: an electrolitic capacitor measure the difference: if small (.47 to 1 uF), near the soil, but more high in "the air", so also the phenomenom expand in vertical position.
A simple 15 to 22 Mohm resistor eliminates iron nails (this is more terrible since nails has sharp end, without this resistor also is an "iron detector" –oxidated–), but if you pass near a stainless steel coin, this detect very well, but only near, suposse for the round form.
With this instrument you can't center well the target, but you can discover how "infernal" can be an only old rifle cartridge buried for long time. So, the nature of the phenomenom is very strong (for this sensitive instrument).
Another important fact is this: this don't detect, for example, a bullett of lead, but if you pass over the target, yes, the old bullett is below the instrument.
A deffect: if you use in high terrains, oscillation of needle (of the uamp), this is, the auto-oscillation, stops, and you can't detect. So, the instrument is manage for environmental or RF in the air...
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