What is this device on the cord for my AC charger, and do I need it?

I have an AC wall charger for an JBL Bluetooth speaker. It has thiscylindrical thing inline in the cord, similar to what you see on some cords that I believe is supposed to reduce RF interference (required by FCC maybe?). But I haven’t seen this on any other wall charger.

Is that what this thing is? Or is it something else that is required for the charger to work properly? My son broke the wire right at the point where the plug comes out of this thing. I could patch the wire if I can remove the device.

I think you’re right - it appears to be a ferrous “toroid” in a cosmetic cover. If it’s as heavy as a chunk of iron you can be sure of it. They’re used on some cables to reduce radiated EMF interference and the wires likely go straight through.

I would probe the wires to confirm the “straight though” connection and eliminate it in a repair.

I thought the purpose of those things was to reduce the RF signals being picked up by the cord. That is, it helps make sure the device being powered has a clean power source. It isn’t absolutely necessary, but it reduces the effects of RF has on the powered device.

That reminds me: What does it mean when the sticker on the device says “This device must accept harmful interference, including interference which causes undesired operation”? In my mind that means the device can’t try to eliminate the interference, but that makes little sense.

I always thought that statement meant that, when exposed to “harmful interference” it would not make the device dangerous. That is, for example, undesired interference will not cause the device to catch fire.

It makes more sense if you think of it as meaning that it bars attempts to unscramble a cable signal.

Explained here. Not all that necessary unless you have electronic devices nearby that are fairly sensitive to possible RF interference. Instrumentation or RF tuners might be one example.

This means that if your microwave oven, or other household device causes this device to not work, or work incorrectly, you have no recourse to the manufacturer. Many devices are built in accordance with FCC Part 15.

So if your neighboring Ham radio station causes the attached device to glow red and emit sparks, don’t go knocking on his door.

I hold an Amateur Extra license, and IMHO going and knocking on his door is precisely what you should do. A nice operator will assist the neighbor with resolving the interference, even if that means installing filters on the customers equipment and paying for them if necessary.

Especially since it’s always coupled with “This device must not cause harmful interference.”

Why must my device accept harmful interference from a device that must not cause harmful interference?

Even if all the devices in your home meet FCC radiated emissions limits there will still be electrical noise events that could be picked up by a victim device, e.g. operating light switches, fridge compressor turning off, car driving past with unsuppressed ignition leads etc.

You can remove and re-fit this ferrite choke by chopping off the moulded strain relief ends, pulling the cable out, and then enlarging the bore with a drill bit or round file before re-inserting the cable and reattaching the plug. The wire would be more prone to breaking in the same way again now there are no strain relief sections, but this can be improved by fitting a length of heatshrink sleeving to reinforce the cable where it goes through the choke.

Alternatively you could buy a snap-on common mode choke to replace the original. I’ve got these things scattered over the house on devices that have been giving me noise issues, mostly CFL light bulbs and things with electric motors.

In almost every case the ferrite is there to cut down radiation from the power cable. It will almost certainly be connected to a switch-mode power supply at one end, or both, and these emit RF.

Electro Magnetic Compatibility (EMC) is at best an approximate business, and I have sometimes suspected that they are added because it’s the only place where EMC precautions are visible from outside “Hey look, we tried!”

Against this hypothesis is the fact that the ferrites are heavy and relatively expensive.

I don’t know the real answer, despite having spent some 10 years in the EMC business.

As a fellow Ham, I agree. I was trying, poorly I see now, to make the assertion that the neighbor has no legal requirement to help or cease operation. I can see that I failed.

This video explains and demonstrates the RFI suppression features of ferrite beads: