Thomas Ashcraft <> wrote:
> For what it's worth, some years ago I was attempting to record meteors=
> by radio at VLF/ELF frequencies on a bluff near Los Alamos, New Mexico.
> The bluff overlooked a canyon that must have had a lot of bat caves. I
> discovered that whenever I turned on my handheld receiver ( a McGreevy
> WR4) the bats would dive toward me frenetically.
>
> I don't know if the VLF/ELF receiver jammed the bats own frequencies?,
> unnerved them? or attracted them? I myself got the message quickly to
> shut down my receiver.
Interesting. A common way to inadvertently attract bats is to use a light (=
headlamp, laptop
LCD backlight) that draws insects; some bats quickly respond to the concent=
rated prey.
A less likely possibility is your gear generated upper audio to low freque=
ncy ultrasound
that attracted them. There is a pricey microprocessor controlled ultrasound=
generator
made by a UK university shop that simulates selected bat social calls to at=
tract them for
study.
> Maybe some sort of electrical force field could be projected around the
> turbine zone to divert the migrating bats from blade dangers.
At low wind speeds, thermal imaging video shows some bats are attracted to =
both moving
and static turbine blades and try to land on them. There is a project evalu=
ating an
ultrasound repeller beacon, but 40 kHz attenuation leads to the view that t=
his will be
uneconomic even if a test unit works (i.e., too many beacons on a grid of t=
all masts
required).
For those interested in the sound of wind turbines, there was conference on=
turbine noise
in Berlin in 2005 and another is scheduled for this year:
http://www.windturbinenoise2007.org/?gclid=3DCLn_lb_browCFQU4YAodUyZLKw
There are diurnal variations in the perceived noise from turbines that rela=
te lower
background noise at night. There is apparently also an effect of infrasound=
modulating
audible frequencies to create the pulsed sound that leads to complaints by =
area residents
(pylon thump):
http://www.ref.org.uk/images/pdfs/Press_Release_20.09.04.pdf
Bill R.
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