but I am of the belief that voltage and current flow have little relevancy in the operation of the two coils you mention. Both voltage and current flow are required, as with any electronic instrument. But the operational characteristics of the coils are based on much more than having enough "power" to make them work. The operational process will be much harder to understand than simply differentiating voltage and current. But let me give it a shot.
Simply put, voltage is the measurement for electrical pressure. Amperage, (milliamps in the case of electronics with 1 milliamp = 1/1000 amp) is the measurement of current flow. And, the final piece of the puzzle being resistance. Resistance, measured in ohms, is a constant. And, in the case of a metal detector, is the resistance to the flow of current through the control panel and the coil assembly. Ohms law tells us that Voltage = Current flow X Resistance.
Voltage is somewhat irrelevant, in this equation in that the voltage of an X-Terra can vary from 8 volts (where the detector shuts down due to high voltage) to a low of 4 volts (when the detector shuts down due to lack of electrical pressure. In other words, the voltage regulator will not allow more than 8 volts of electrical pressure drive the current through the circuitry. And, if there is less than 4 volts of electrical pressure, there isn't enough to push an adequate amount of current through the circuitry. So, the high and low voltages for an X-Terra would be less than 8 and more than 4. As to how many electrons it takes to operate just the coil???? I don't know. You could determine that with an ammeter, in series with the transmit circuit or receive circuit of the coil. Or you could measure the resistance of the coil and do the math. However, knowing that there is a micro controller in the X-Terra coil, I ain't going to be hooking anything up to mine except the control housing.
As to why some detectors take AA batteries and others take 9 volt batteries..... that is simply different design and engineering techniques. As long as their is ample voltage to provide the electrical pressure required to push a sufficient supply of electrons to drive the circuitry, and it fits in the housing, it don't matter. The total number of electrons available to continue the operation of the detector is more important. As an example, you can buy NiMH AA cells with 1800 mA or you can buy them with 2700 mA. Both offer 1.2 volts base pressure. (fully charged is closer to 1.5 volts). But the number of electrons willing to be pushed through the circuitry in the 2700 cells is half again more than the 1800 mA. In other words, the 2700 cells should last 50% longer between charges. And, as long as there is sufficient electrical pressure to push them through.
As to comparing the 10.5 inch Explorer coil to the same sized X-Terra coil, I wouldn't call either one of them basic. As I mentioned above, the X-Terra coil has a microprocessor imbedded in the coil. In addition to the current flow required to generate magnetic lines of force in the coil configuration, it takes a small amount to power the communication chip. How the microprocessor in the detector housing communicates with the microprocessor chip in the coil is still proprietary information.
As to the coil requirements of the Explorer, I haven't done any specific testing. But I've read there is a multi-tone generator on the transmit side. The receive side uses a sampled data system followed by a Digital Signal Processor based Fast Fourier Transform.
I'm not convinced that the Explorer actually transmits 28 frequencies at one time. Instead, I think the Explorer looks at 3 frequencies and selects those from a 98.5 KhZ spectrum. This spectrum contains 2 main frequencies and their associated harmonics. I say this because from what I understand, the Explorer transmits square waves from two separate time frames, which would represent 2 different frequencies. If they do transmit square sign waves, and square sign waves are comprised of 2 different frequencies, and, square sign waves are comprised of odd numbered harmonics (3,5,7,9 KhZ etc), then if you transmit one square wave of 3 KhZ and one at 15KhZ, then the actual frequencies in that waveform would be 3,9,15,21,27KHz,etc. in one part and 10,30,50,70,90KHz etc in the other.
After this brief and confusing post, I guess my point is that voltage and current flow have very little to do with the operation of the coils on an X-Terra or an Explorer. As long as their is ample voltage to push enough electrons through the circuit, it will work as designed. If the voltage is too high or low, they shut down. Now you can't get any simpler than that!
HH Randy
