Locating RFI in a home

[brandon7861]

I recently built a wire tracer/toner for use with energized circuits, and although that is a topic of its own, I ended up with a tool excellent for locating sources of RFI.

The problem with tracing energized circuits is that there is a transformer and a bunch of other things connected to the circuit which loads down the signal from the toner. E-field probes are nearly useless for tracing that as all that signal voltage gets shorted out. But the current is still there. What I ended up doing for the receiver was replacing the E-field probe on my headphone version Carlson Super Probe (youtube has that project, channel Mr. Carlsons Lab) with a multi-turn H-field probe (and some filtering). This allowed me to follow the toner signal along the wires, but I was also able to clearly find which breakers had noise on them as well. Going along all the cords plugged into the power strip under my desk, finding the noisy ones was a breeze. No more guesswork. I can locate all the noisy stuff in a house in a matter of minutes with that probe and not turn off a single beaker. I can even hear the data on my starlink dish cable. My H-field probe consisted of about 15 turns of #28 enameled wire with a winding diameter of about 1" and aluminum foil shielding (split), but I am sure that was overkill as I need to use the gain control on both the transmitter and receiver to isolate the toner signal on an individual breaker.

 

[brandon7861]

With fiber coming down our road and starlink raising our rates, I signed up for the fiber. They flagged the route in the yard yesterday. I thought I would mark on the exterior wall where the studs, floor and outlet wiring is so they know where to drill through. Building code aside, I wanted to be sure they didn't hit an outlet wire.

The probe mentioned above didn't get the job done, the wall was too thick. Came up with something just about anyone could do with minimal parts.

I set my old koolertron signal generator to 54MHz and drove the neutral-ground pair at the outlet (they are bonded in the panel). I used the same pickup coil as I used in the post above, 15 turns on a plastic form with an SMA connector soldered on, and this time connected it to a handheld scanner. I was able to easily follow the wires in the wall with the s-meter on the scanner. I had the sig gen connected directly across the two leads with no load resistor and had the amplitude set to .024v. It didn't take much power to get a usable signal through the wall and into the scanner, and the coil made it easy to narrow down the location.

I did try 25MHz, as that is the lowest the scanner works on, but 54 gave me a sharper/narrower signal when sweeping over the wall which made it easier to locate. I know signals in the MHz can easily couple into adjacent lines, but I just wanted to know where not to drill. If telling one line from another, frequency matters much more.