TV or display buzz
Broadband noise from plasma TVs and some displays or their power supplies.
What does it sound like?
A buzzy hash with a steady low rhythm, starting and stopping when the screen is switched on and off.
Who uses it?
Not a station: a screen in your home or a neighbor's.
Where and when can I hear it?
Across shortwave, especially lower frequencies.
The science
A plasma screen is a grid of tiny gas cells, each glowing like a miniature neon sign. To keep lit cells glowing, the set drives them with trains of roughly 200-volt pulses at several hundred kilohertz, and a patent on reducing that radiation identifies the large, fast current surges from those pulses as a main cause of unwanted radio emission.
Why it matters
The ARRL's quickest test is that noise from the plasma panel itself changes with every scene change on the screen. You can sometimes match it to a channel by flipping your own TV through channels until the scene changes line up with the noise.
Lore
The plasma display was invented in 1964 at the University of Illinois by professors Donald Bitzer and H. Gene Slottow and student Robert Willson for the PLATO teaching computer network. They received an Emmy award in 2002.
Easily confused with
- Power-line noise: power-line noise doesn't follow a screen being switched on