Updated: Jul 6
This will probably be a controversial topic. Many people love their K-II meters and damn near worship them.
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 essentially reverse engineered them with some help from a couple other highly skilled electronics engineers.
We, together, made some discoveries you'll want to know about.
How the K-II Really Works
The EMF meter that we found most troublesome was the K-II.
First, let me say that Biddle’s blog post about the K-II is wrong. The only thing he got right was the on/off switch. What he called the “EMF sensor” is actually a common op-amp. It is the LM324 op-amp used as a comparator.
What that means is that the sensor reads a voltage generated from antenna that is boosted by a series of transistors. If that voltage is above a threshold, it lights the LEDs. The higher the voltage generated by the EMF, the more LEDs light up. It’s a very simple, yet effective circuit.
Sounds good so far, right?
The actual sensor is the coplaner loop antenna itself. When electromagnetic fields are present, a tiny voltage is generated in the loop and read by the op-amp. That’s it. Very simple. (The signal from the coil is small. The coil signal is run through several step-up transistors for a gain of 200+. The voltage the LM324 sees is ~2.2+ volts.)
The Problem with the K-II Meter
The issue we discovered was in 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.
Think of rectification as a net catching the analog signals and turning them into digital signals. In this case, some of the analog signals get through the net.
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.
Both of these outcomes lead into a false positive, and there is no way of knowing when it will happen.
Why I Don't Use a K-II Meter
Personally, I prefer not to use a K-II Meter for this reason. It's important to remember that anything created by humans will have imperfections, some more noticeable than others. That's why it's always a good idea to rely on our own knowledge and intelligence, rather than solely on a device.
Above all else, let this be a lesson to learn about the products we buy into. If someone says a tool is good for X or Y, it's important to make the final decision for yourself.