Electric fence ticks
Regular clicks from electric fences, especially where plants or wet grass touch the wire.
What does it sound like?
A sharp tick or pop about once a second, like a slow metronome.
Who uses it?
Not a station: farm or garden fencing.
Where and when can I hear it?
Across the lower bands, often worse in wet weather.
The science
A fence energizer sends a short high-voltage pulse down the wire. The international safety standard for energizers, IEC 60335-2-76, allows at most one pulse per second, each no longer than 10 milliseconds when measured into the standard's test load. The ARRL says radio noise from a fence is not normal: wherever the pulse jumps a gap, at a corroded gate hook, a bad splice, a cracked insulator or a weed touching the wire, it makes a spark, and the long fence wire acts as an antenna. The ARRL notes this noise can disrupt reception more than a mile away, heard as a tick-tick-tick in time with the energizer.
Why it matters
The noise usually means the fence is being damaged too, since the spark eats into the wire at the fault. It can come and go as weeds grow into the wire, burn back and regrow, and an insulator fault may change when it rains. Under FCC rules, the fence operator must correct noise that causes harmful interference to a licensed radio service, and the ARRL says the fix is usually simple maintenance by the fence owner, often at no cost.
Lore
The ARRL warns of a look-alike: some electric blankets and heated mattress pads make a pulsed noise much like a fence, and certain models do it even when switched off, until unplugged.
Easily confused with
- Power-line noise: power-line noise is a continuous buzz