Broadband internet or powerline network noise
Noise from internet service over phone lines (VDSL) or from powerline networking adapters that send data through house wiring.
What does it sound like?
A steady, hissing roar, like rushing water, over whole sections of the band.
Who uses it?
Not a station: nearby internet equipment.
Where and when can I hear it?
Blocks of raised noise across wide stretches of shortwave, sometimes with quieter gaps.
The science
Both technologies push high-frequency data through wires that were never designed to carry it. VDSL2 sends thousands of closely spaced carrier tones (a method called discrete multitone) over telephone pairs, reaching about 17.7, 30 or 35 MHz depending on the profile, and those frequencies overlap several amateur bands; faulty or unbalanced wiring can let the tones radiate as broadband noise. Powerline adapters do the same over house wiring: HomePlug AV uses 1,536 carriers from near DC to 37.5 MHz, but its North American transmit mask switches off the carriers that fall in amateur bands, so the noise can have quiet gaps there.
Why it matters
The noise sounds like a steady rush because it is many data tones packed side by side. An early ARRL field test of a pre-standard VDSL system found no widespread interference where telephone wiring was underground and well maintained, while noting that damaged wiring would be a correctable defect. The ARRL reports no harmful-interference reports from HomePlug or HomeGrid adapters, which it credits to their amateur-band notches.
Lore
Utility-scale broadband over power lines, which the ARRL says can make as much noise as 1,000 to 10,000 devices under other unlicensed-device rules, led the ARRL to take the FCC to federal court. In 2008 the court sent the rules back to the agency, which largely reaffirmed them in 2011, and most commercial deployments have since shut down as uneconomic.
Easily confused with
- Digital Radio Mondiale (DRM): DRM is one 10 kHz block, not whole band sections