Note: Alessandro reported recently that he has identified the noise!

Dear Ken,

I find the noise source! It is a television set about 50 mt from my antenna in the north direction in the last floor of a condominium near my house. It is a Shaub Lorenz 20" stereo TV set made in Turkey. I belive that was a power supply mistake, but probably the noise came from the tube screen. At moment I cannot eliminate the noise, probably I will change (my charge) the TV with a new one HI HI.

Alex IT9YHR

Your website also helped me locate another source of interference, my two Ionic Breeze units! THANKS! -Web

Anyway, there is no manufacturers name on the blanket or control.  But it was made in China and distributed by Bed, Bath and Beyond.  The unit was only plugged in and not being used. The small remote (heating control) was sitting on the bed stand, was triangular in shape and had a round knob on it with large numbers 1-10.

Thanks and great site...K2WH

P.S. Dom if you read this, I found the source of the signal as described above.

Thanks Bill. Compare this with the recordings of electric blanket noise from the ARRL Lab below! ...Ken

My neighbor a few doors north of me had one installed in his garage in an attempt to control bugs in his house. It's been installed for 6 months, just as long as I have been hearing the RFI. The RFI was strongest on my truck's AM radio (1600 KHz) right in front of his house, but I could still hear it 0.5 miles away.

I caught my neighbor outside while he was taking down his Christmas lights. He was nice enough to let me wander around his house with a portable radio, within 5 minutes we located the source. Flip the off-switch and poof, RFI is gone! He agreed to leave it off until he can contact the maker to fix it or remove it. He agreed to call me before he turns it back on (what a nice neighbor!!). He also admitted that it did nothing to control his bug population problem, saw no measurable change in 6 months. The product sounds like a perpetual motion machine to me, but I know nothing about bugs. All I know is that it was extremely aggravating to try to listen to any radio within the frequency range of 1-15 MHz, my house is about at least 500 feet from his.

You should put my post on your RFI web page. I could still hear the RFI about 0.5 miles away - makes me wonder if the contraption is actually RF-type accepted or not. The Repel-tron made 1-15 MHz useless and very frustrating to use, and wiped out my daughter's AM radio too. She likes to listen to a station at 1580 KHz - Repel-Tron successfully took it out.

I'd like to make sure some other ham or AM radio-phile that lives by one of these things can at least recognize the sounds from the MP3 recordings. It makes me angry that such an RF noise generator can actually be sold!!"

I have one of the bad ones on my bench and see that the center frequency depends on the voltage and current present at the charging terminals. As the battery charges the center frequency moves across the VHF high band. The rapid sweeping is from the AC ripple from the wall transformer when loaded due to battery charging. The modulation frequency is 60Hz.

The battery charger is the cause of interference in the high VHF radio spectrum, 140 to 170MHz, and is caused only when the cordless telephone handset is placed in the charging cradle. The interference appears as a rapid swept frequency, six megahertz in width, anywhere within the VHF high band spectrum. The battery charger is the cause of several sources of interference on two meter amateur radio repeaters.

The interference is best described as a buzzing sound with an approximate one second duty cycle. The interference has been heard in several locations, two of which are the source of the interference heard on the repeater input located 2500 feet from the source at an RF level of -80dBm. Directly in front of residence that contains one of these chargers the RF level measured -40dBm. "

Every other harmonic is stronger, as expected.

The MP3 file was recorded with an ICOM R-20 in AM mode, with the filter width set to 15KHz. In this case, the frequency was 3200 kHz. The antenna was a simple shielded, tuned 80M loop made out of RG-58 coax."

The noise I heard lasts for about 1 second and repeats every 24 seconds. I now suspect that it may be a wall-wort or battery charger since my next door neighbor is a building contractor and he has been building a new garage for months now. I DFed the noise and it points in the direction of his garage (or houses on the other side of course)so that may be a clue.

I heard it 24/7 on every band from 40M through 6M. I didn't check anything higher than 6M and my QRN level on 80M was too high to hear it. I heard it loudest on 40M and 20M."

(This is a long file, about 51 seconds. I left it this way because I thought the long gaps between occurrances of the noise might be a clue....Ken, VE3HLS)

Additional Information: Chad Wahls of the University of Illinois has had some experience with this type of equipment and offers this additional insight [Click Here]