Re: Hey Boffins!!!
DropBear posed, "...both would experience the same modulation..."
Clever design would have the modulation only exist (at significant power levels) in close physical proximity to the horn. This is a trivial requirement to achieve. Then, if the modulation frequency signature shows up in the detected thrust, then you know that the thrust is probably originating from that circuitry (the high power circuitry carrying the tone) or the horn itself. It eliminates the high power DC circuits, as they don't carry the tone.
It makes the detection simpler, but (and you're correct on this point) it doesn't explain where it's coming from. Except it DOES help in narrowing it down to those parts which carry the tone at power. Eliminating the torque effects caused by the DC currents at the liquid joints * would be critical.
(* Ref: Google this -> liquid mercury motor)
The second suggestion about the applied magnetic field is what would be added to the experiment a few days later, to help track down the source. It would be a different frequency tone, identifying the thrust as having a magnetic field origin.
It merely a technique, to make use of the vast frequency spectrum to separate signals from the endless offsets of DC, and from each other. This should be second nature to experienced experimentalists. All they need to do is think about it, and then include it. It makes experiments better, faster and cheaper.
Biting the hand that feeds IT
