An idea about a noise "canceller" (and a request for opinions)

you are right, Ivan, and I had the same doubt, but then... most noise from underground cabling is at low frequencies, so outside the "receive window" of a decent receiver with frontend filtering, there may be harmonics, sure, but I believe those may be handled by adjusting the level of the 180° output, no ? Also the conducted (along the wiring) noise will have much lower level so the filter should still be able to eliminate "domestic" noise, it may have some low level residual background, but again, adjusting the level, it shouldn't be a problem

Hi Andrew,
my opinion is it would not work. There are lots of spurious signals on the AC line, which are not picked by an antenna. Such a device would bring them (180 deg shifted) to the input of your RX. This would be true especially where the AC lines are buried in ground. It might work better with the AC lines hanging in the air, but some cancellation of useful signals would probably take place. (Air power lines are a good longwire untuned antenna. They even used to be recommended as MW AM antennas, until some fatal injuries happened due to a faulty capacitor.)

VBR from Ivan

Folks, I've been thinking for quite some time about the noise generated by various electrical devices, be those switching PSUs, inverters, induction ovens, faulty/sparking transformers placed on the outside mains lines and then some; all that noise is in most cases both "transmitted" along the AC lines and radiated, and picked up by our antenna

Now, let's look for a moment to the so-called "X-Phase noise eliminator", here is an example of the circuit (but it's easy to find other versions)

https://vk5tm.com/homebrew/noisecancel/noisecancel.php

basically the unit uses a "noise antenna" (probe) which should be configured to receive more noise than signals, then the input from the probe is fed to a circuit which allows to adjust the phase and gain so that the "noise" signal gets phased by 180° and then mixed with the signal from the antenna, resulting in THAT (and only that) noise being removed, now... the main problem with this circuit is that it can only remove ONE type of "noise" at a time, at this point here's my idea (probably crazy, and I'm asking for your opinions)

Let's say that instead of a "noise antenna" we use our AC mains line, we insert a plug into a wall outlet and use (say) a 1KpF/1KV capacitor to pick up "signals" from the powerline, at this point if we use a scope or an analyzer we should be able to see most of the "domestic" (and nearby) noise generated by the various sources and which we also receive through our "regular" antenna, till now nothing special, but...

In this case, we're picking up "signals" (ok noise) from the AC line, but while the "X-Phase" has no idea about what is signal and what is noise, we now KNOW that the "good signal" there is just the AC 50Hz  (or 60Hz in US) and anything else is just noise, so here's the idea, we feed ALL that signal ... ok, noise (no tuned circuit) to a phase shifter circuit which shifts everything by 180°, done that we adjust the output level to more or less match the one of the noise picked up by our antenna and, finally we mix the output (noise shifted by 180°) with the signals+noise picked up by our regular antenna and feed the result to the receiver

If I didn't miss something, the result should be the cancellation of the various electrical noises and possibly a clean reception, sure, such a unit won't help with far away noise or with atmospheric noise, but I think it may tame the noise from switching stuff, and all those other "domestic noise generators", be it from something in our house or in the neighbourhood

But then, I thought that, if it was so simple, someone else should already have built such a thing, so probably I'm missing something, so I'd like to hear your thoughts