Well great. Found out my monitor generates RFI equal to the refresh rate. Gotta see if toroids on the cables will fix anything.
@kilroy_was_here Vertical refresh rate EMI or much higher frequency hash and buzz modulated at the vert rate? Do you have a spectrum analyzer to sniff it out?
On my AM radio, when the refresh rate is 75, there's a 75Hz buzz at certain places on the dial. Change it to 60, the buzz changes to 60Hz but it's in different places on the dial. Same thing at 50Hz.
@kilroy_was_here @Spud_Coolzip It sounds like the interference is happening in the audio frequency stages of your AM radio, rather than RF. Have you tried other radio receivers? It might just be a poorly shielded radio that needs to be kept a distance from noisy electronics. 75Hz "noise" shouldn't propagate very far without an extremely large "antenna" to to work with.
Take a look at this. You're thinking the radio is further from the screen than it is.
Experimental experience would disprove the audio interference hypothesis. It doesn't cause audio modification, it causes stations to be blanked out.
The non-contact voltage detector on my multimeter also goes off within a foot and a half of the screen.
This screen just wants to be seen on more spectra than one!
@kilroy_was_here @Spud_Coolzip Maybe we were misunderstanding each other. The closeness and the fact that your multi-meter goes off both indicate the RF is in the audio frequency range (double or triple digit Hz) rather than the medium wave radio frequencies. That would potentially get into the radio right before the audio amplifier stage and overwhelm the audio. Also, love the look of those SANGEANs.
@kilroy_was_here @Spud_Coolzip The solution, unfortunately, is likely to either move the radio further from the screen, or get lucky with another screen that is extremely well shielded. Adding some ferrites to the monitor's power lead might help a little, but will still benefit from distance. I have almost the same issue with some under-counter LED lights. The wall wart needs to be a few feet away or better.
@ve3mal @kilroy_was_here Depending on how well the meter was designed, it may have an RF rejection and filtering problem. RF can get into op amps and instrumentation amps, where it can be rectified by parasitic diodes, and inject offset currents or voltages. I'm currently working on yet another RFI mitigation design for a smoke and gas detection product. It's been the same type of problem almost every time.