Posts by DaveGadgeteer

AC coupling doesn't solve it, that doesn't disconnect the scope probe ground clip from the chassis or from the safety ground.

All AC coupling does is block the DC component of the signal, which is not the problem here. The spurious current here flows in the ground path, not the probe-tip signal path.

I see their scope has two probe inputs, "channels". If they used both, put one probe on each end of the resistor, and left the ground clips hanging, they could subtract (or, often, invert one then add) channel 2 from channel 1 and ideally see the real voltage across the resistor without providing this massive path to ground. Tying the two ground clips together might reduce noise somewhat. To get clean signals to subtract nicely, you might have to tie the grounds to one semi-isolated almost-floating point, with finite impedance to ground but large enough to block any spurious heating currents. You can temporarily connect the two probes to the same point to ensure that the gains really match (adjust until they do) and the subtraction really results in zero. The loop formed by the two scope probe cables will pick up EM noise, so keeping that small helps--perhaps loosely twist the probe cables around each other.

The setup as apparently used could easily add 20 watts to the test device chamber through the ground connection, without any visible evidence. But if the device keeps heating while the scope ground clip is disconnected, then this cheat was not being used.

In the attached figure, I added to Mats' test circuit diagram in orange, to show how easy it is to inject arbitrary electrical power into the eCat as demonstrated.

This cheat could be tested for by disconnecting the scope probe ground, and seeing whether the eCat continues to heat without that connection.

Was that tried?

Or, the problem could be avoided by using a battery-powered scope and carefully isolating it from ground.

The power input by the control box into the reactor was not measured, and that is a crucial part of the demo. The resistor and load swapping method used was not convincing to me.

Nobody seems to have investigated the possible use of the invisible ground circuit through the scope probe back to the control box. That could easily carry tens of watts. Does the reaction continue to run when the scope probe is disconnected? That problem could have been avoided by using two scope probes subtracting before display, a differential setup, with their ground clips tied together but not touching the demo, just floating. Then the scope would be high impedance, unable to disturb the power flows significantly. But any electronics tech knows that significant current can flow through the ground clips. I noticed that there was a point in the final resistor swapping stages where the ground and scope probe tip had to be swapped to get the signal to look right on the scope, and I didn't think it was just a problem of the signal having the wrong polarity. But I suppose we'll never know.

Nobody except Rossi knows how much electrical power actually flowed from the control box into the test.

Other than that, the calorimetry part looked trustworthy, so 20 watts more or less was provided in the eCat.

We just can't tell where it came from.

The oscilloscope appeared to have a single-ended probe connected to the resistor.

The ground clip of such a probe is essentially an earth connection to the power grid.

Why couldn't significant current flow from the exciter circuit through the scope ground clip? The exciter presumably also has a connection to the safety ground or earth, so that can be used to carry unmeasured current.

It's a terrible pity that the input power to the Ecat was not measured.

The camera happily recorded scope traces that presumably contain the secret info Rossi supposedly was trying to protect.

I had hoped for a transparent demonstration, but this one isn't persuasive, I'm sorry to say.

If your mains are varying a lot, that might make it worth a change in power strategy.
Have the mains feed a switching power supply that puts out regulated DC at a high enough voltage to run your resistive heaters. Switching supplies have gotten quite inexpensive for a few hundred watts.

Then inject whatever electromagnetic noise you want to try, either into its own coil winding or, perhaps easier, isolate the heater coil from your regulated DC using an inductor/choke and capacitively couple your noise signal to the heater coil.

Or, you could transformer couple the noise to the circuit--have a high-current-capable secondary in series with the power supply and feed your noise into the primary. If that varying load current makes your supply unhappy, add a big capacitor across the supply output.

Then you could experiment separately with noise waveforms and temperature.

Actually, another approach could be easier--since you need to computer control the supply output anyway, in order to change the temperature, you could use a fixed-voltage switching supply just to isolate yourself from the power mains, and both vary the average DC level to control heating and also vary the pulse characteristics to produce the noise characteristics you like. There are a few very fast GaN power transistors available now that could make some pretty sharp signal edges.

But who knows what kind of electromagnetic noise is needed or helpful...