I’m an avid AM broadcast DX’er. On my nightstand sits a Zenith Transoceanic with a headphone plugged in. I fall asleep spinning the dial. It goes without saying that any source of buzzes, drones, fizzes, sizzles, or other unwanted QRM gets hunted down. I’ve gotten pretty good at it, or so I thought.
So about a week prior to writing this, the wifey bought an inductive charger for her phone. I noticed it because there was a blue glow from her side of the bed and I know she’s not radioactive so I had to investigate. So here’s this TEMU looking device with a blue hover light all the way around it’s bottom edge. Cute.
At the same time, I got plagued by a buzzing QRM between stations on AM broadcast. It was practically wiping out all DX. Only the local stations were getting over it. Crap… how do I break it to her that her cutesy TEMU charger has become my nemesis? A couple of days went by since I mentioned it and the noise was still there. No AM DX for me.
Jump forward a week from the time the charger showed up. We’re both home so I decide to hunt down the noise. I like to do it with her present so she can see first hand what the offending item (typically a USB phone charger) is doing.
I went back to the Zenith and the noise was still there, flooding the dial as loud as ever. I flip off a few switches (didn’t want to directly accuse her new toy) and go check. Nada. She then tells me she had unplugged the charger a few days back. UM WHAT? Uh oh… Now I’m stumped!
Rechecked the bedroom outlets for wall chargers but found nothing. In rummaging around my nightstand, I accidentally knocked off the alligator clip that connects my outdoor wire antenna to the Zenith. That caused the noise to drop. Ok, we got something here. It’s either right here or outside coupling to my antenna wire.
Right here where though?!? Nothing is plugged in other than my lamp and the transformer that runs the Zenith. I turn off the lamp since it’s an LED bulb to see what that does. No change. There’s an outdoor solar floodlight right near the wire antenna. Could that be it? Insert head scratches here.
The head scratch must have increased the blood flow to the solitary neuron holding up my hair because I had an AHA moment! My nightstand bulb has built in battery backup. Could that be it? I reach in, unscrew it from the socket and BAM, noise is gone!
It now all seems kinda “duh” but let me fill you in on what made this a not so obvious problem.
The bulb in question is a Feit battery backup LED Edison base bulb intended for common household lamps. The way it works is if power goes out and lamp switch is ON, it detects it and turns on at reduced brightness using an internal LiPo battery. While working off the switch it acts like any other bulb. Out of the socket it’s off like any other bulb. Short the contacts on the base though and it will turn on. Perfect for doing Uncle Fester tricks on Halloween.
Switching the lamp (and thus the bulb) off did not get rid of the noise. Something failed in the circuit causing RF hash that was kept alive by the battery despite the LEDs weren’t on. Why was the QRM level affected by my wire antenna? The wire antenna runs parallel to power cord for lamp. It was coupling.
In the pics you see the bulb disassembled. Nothing obviously wrong. Typically you’ll find bloated or leaking chinese caps in failed LED bulbs but not this time. Battery wasn’t a spicy pillow either. Without diagnosis, there’s no smoking gun. It lasted about 4 years. I can’t complain. Was a good learning experience though!
