Re: Listening to TC?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Aaron Jagt by way of Terry Fritz <teslalist-at-qwest-dot-net>" <aaron-at-entrewave-dot-com>

It's a neat idea, but I don't think that is what happened. The bat was
probably scared.
  From personal experience, I had a bat fly into my home, through an open
padio door. It flew around in large figure eights, after each one trying to
fly through the door. After about the third try it missed the open area
(about 3' by 7') to the outside, smashing instead into the glass door beside
it. I picked it up  and gave it a push outside, and it took off outside.
   If it had been a bird, I would have thought it just didn't see the window,
but since a bat uses sonar I think it was scared out of it's wits. (I have a
high idea of the ability of a bats sonar, I once read a story of a bat a man
had made friends with: the bat was flying around this guys room, playing
around,and then headed directly toward the open fan that was blowing.at 80
rounds per minute--- and through the moving blades, doing this a couple of
times. After the fan had been speeded up to 300 revolutions per minute the
bat would no longer fly through.)
  So, you can draw your own conclusions about it I guess.

Aaron J.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, June 20, 2003 8:33 AM
Subject: Listening to TC?


 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<Mddeming-at-aol-dot-com>
 >
 > Hi All,
 >
 >         We all know that spark gaps and streamers make some pretty awesome
 > sounds, but what about "ultrasounds"? These would be sounds from 15KHz on
 > up to the resonant frequency of the coil. This question is prompted by the
 > following: Last night, a bat got into the instrument/people section of the
 > lab. (The TC section is inside a grounded 10ftx10ftx8ft cage). With the
 > coil running, the bat ran into the wall the way a bird or insect will beat
 > against a window trying to get out. I turned off the coil and it
 > immediately turned around and flew back out the door which was only open
 > about 5 inches.  Makes me think maybe the coil was making sonar-jamming
 > noises. Of course, it could be pure coincidence.
 >         Seems about 35-40 years ago, I read about an "ultrasonic listening
 > device" that used a very (for that time) high freq. response ceramic mike
 > and heterodyned its output with ~38KHz local oscillator which made sounds
 > above 20KHz audible but inverted. Example: a 32 Khz "sound" would become a
 > 6Khz tweet, while a 37KHz one would become a 1 KHz beep, etc. By making
the
 > local oscillator a VFO, one could listen to a wide range of the audio
 > spectrum up to the response limits of the microphone.
 >         If nothing else, such a gizmo might add to the "Halloween value"
of
 > a coil. Does anyone know if such devices are still around in a modern
form,
 > or if there is a microphone/transducer with good well-above audible range
 > frequency response for a DIY?
 >
 > Matt D.
 >
 >
 >