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Why I don’t use a K-II meter.

This will probably be a controversial topic. Many people love their K-II meter and damn near worship it. The K-II was designed to find live wires in walls, like a stud finder for electricians. Grant Wilson made the statement in the early days of the Ghost Hunters TV show that the “K-II was calibrated to find ghosts”. Since then, ghost hunters have been using the K-II without question.


As an engineer I had questions about the design and accuracy of the K-II and a few other EMF meters. So, I did a deep-dive exploration into these EMF meters. I, in a sense reverse engineered them with some help from a couple other highly skilled electronics engineers. We, together, made some discoveries.


The one that we found most troublesome was the K-II. First, let me say that K. Biddle’s blog post about the K-II is totally wrong. The only thing he got right was the on/ off switch. Biddle is not an electrical engineer, nor any kind of electrical expert. What he called the “EMF sensor” is actually a common op-amp. It is the LM324 op-amp used as a comparator. What it does is read a voltage generated from antenna and if that voltage is above a threshold it lights the LED’s. The higher the voltage generated by the EMF the more LEDs light up. It’s a very simple, yet effective circuit.


The actual sensor, is simply, the coplaner loop antenna. When EMF is present a tiny voltage is generated in the loop and read by the op-amp. That’s it, very simple.


The issue we discovered was the rectification circuit that turns the positive portion of the analog voltage signal into a digital one right before the op-amp. Rectification is a way to convert analog waves into digital signals. This can be done correctly several different ways. It can also be done incorrectly. If done incorrectly, part of the full wave will get through.


The K-II does a poor job rectifying the analog signal. It will allow negative voltage to pass. When this happens the LM324 op-amp will become unstable. One of 2 things will happen. Either nothing will happen until it settles down or it will peg red until it settles down. This leads into a false positive, and there is no way of knowing when it will happen.


For this reason, I do not use a K-II Meter. Anything made by man will have imperfections (some more than others), so it is important to be smarter than the device.


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