On Nov 17, 4:09*pm, wrote:
On Wed, 17 Nov 2010 15:46:57 -0800 (PST), "

wrote:
I've heard this at other places on shortwave. At first I thought it
was something natural like the sun or the ionosphere. But now I wonder
if it's power lines. It sounds like a cycling industrial (machine
like) sound. Does not alter much and has some phasing and echo /
reverb.

Does anyone know what this is ? I have a recording somewhere that I'll
try and dig out.

From the frequency and description, I would say it is CODAR (pulsed
radar). It sweeps a span of frequencies in this area of the spectrum.

Jim

Yeah CODAR can be heard here in many of the
HF Bands a 100 Miles from the Ocean.

CODAR : Coastal Ocean Dynamics Applications Radar
http://www.esrl.noaa.gov/psd/

CODAR is used to measure the surface currents
of the coastal ocean.
http://marine.rutgers.edu/cool/codar.html