https://youtu.be/4XyqMayYElcRolling QRM. It starts fast, slows, then stops. When it stops, the interference is present for 12 hours. Some have suggested this is Grow Lights RFI.
The fast rolling begins at roughly at the 2 minute markIt lasts approximately 5 minutes before stabilizing, just like the ARRL states.
http://www.arrl.org/grow-light-rfiGrow lights tend to exhibit several unique and identifiable characteristics. So far, they typically produce a broad band noise, particularly across the 40m band. It propagates over much greater distances than one might expect from devices that meet the applicable FCC limits. Other clues include:
- Generally grow lights are set by a timer for 12 hours on and 12 hours off but this can vary
- Once you have established the turn on time, listen to the noise as the lamp turns on. It’s generally noisier with less of a flat spectrum. This generally lasts about 5 minutes until the lamp is warm
Now ... how do I locate the source in a densely populated neighborhood? Homes, homes, everywhere ..