The AM Forum

Local radio station KTRC AM @1260 KHz has a neat Sunday afternoon nostalgia show that I wanted to hear the other day. I flipped on two different portable radios at opposite ends of the house, one a Chinese SW/AM/FM and the other my favorite Panasonic RF2200. Both had a horrible buzz that completely obliterated the AM radio band. KTRC is 5 kW and 20 miles away, so I expected to hear something there as in the past. I didn't even get around to firing up the ham rig. I started troubleshooting by unplugging various wall warts (amazing how these things seem to multiply, phone chargers, Bluetooth speakers, etc). With no improvement, I tried light switches. The kitchen overhead track lights were the problem. I had converted to LED from PAR20 or PAR30 bulbs years ago. There was a mix of four different brands of LED floodlight bulbs. One by one I unscrewed them until I found the culprit. It was the oldest one, a non-branded aluminum-finned light that I had bought at a hamfest from an Arizona LED seller. This one bulb was a very strong source for broadband RFI. With it removed, all the buzz was gone and radio reception with AM mode became good again. The LED bulb likely didn't meet FCC part 15 R&R while it still provided decent light. Now its in the trash.

  A lot of the Wall Warts are switching supplies now for energy efficiency. I had a station set up in my sister's family room in her basement while I was visiting in MA. There is a military radio net on 3885 very early Saturday morning I wanted to check in to. There was RFI right on 3885 and as I did some further investigation every 100 KHz, above and below that frequency, 3785, 3985 and so on. It was the wall wart for the wireless router which was also in the same room.

In a house or office building with lots of "suspects", start throw the breakers one by one until things get quiet.

That narrows the field in a hurry.

An amplified FS meter is also useful.

:-)

I'm slowly converting all the light bulbs in the house from the mix of incandescents/CFLs that's here now to Cree LED bulbs as the old bulbs die one by one. The Cree bulbs seem to be the cleanest RFI-wise, at least down at HF. It seems that what little hash they do make is at VHF and at very close range to the bulb, i have one bulb in particular that wipes out reception of a digital TV station that transmits on channel 7, but another out of the same pack doesn't.

  "In a house or office building with lots of "suspects", start throw the breakers one by one until things get quiet."

   A good procedure, I did RFI complaints for the local power company before I retired. Shutting off breakers one at a time or brute force hitting the main breaker while powering the receiver off a battery is a good way to determine if the RFI is coming from inside the the building. I had a ham who had bad RFI, it was the fluorescent light in the parking lot behind his home, the light was on all the time.

 But when the light was shut off the RFI went away, turning the light back after it had cooled for a time changed the characteristics and frequency of the RFI, waiting 5 or 10 minutes for the light to reach operating temperature brought the RFI back to its prior characteristics.

RFI has hit a new high...or is it low....with RF garbage from modern electronics.   Does the FCC enforce part 15 any longer?  Transformer based power supplies for consumer electronics have all but disappeared. And the RF crap is getting knee deep ;D. 

Wife got a automatic vacuuuuum cleaner for xmas.  It works well.  Wiped out 75 meters too.  Had to shut it up with lots of ferrites....even then I can still hear it at a low level.  Reminds me....I need to order more donuts (the kind you dont want to eat)...going to need more. >:(

~ps