Topband: `Fishing buoys`

[Terry]

I see regular references on here to coded `fishing buoys`. What, 
however, are the increasing number of beacons on top band - presently 
from 1810 right up to 1823 - which seem to warble, or toggle between two 
slightly different tones ? These beacons are not coded - at least not in 
morse.

These seem (from extreme southwest G) to be coming from between north 
and east - and would generally seem to be strongest when the band is in 
good shape.

The beacons are increasing in number and creeping up to around 1823 ...

Thanks in advance for any info !

Terry
G4AMT