🚀 go-pugleaf

In article <1990Feb5.162926.3877@pcsbst.pcs.com> jkh@meepmeep.pcs.com (Jordan K. Hubbard) writes:
>Here in Munich, during the summer evenings, we have lots of Bats
>that congregate over the river to munch on winged insects and other
>savory morsels. I've often sat watching them swooping around, wishing
>that I could somehow eavesdrop on their guidance signals and see how and
>when they "ping" their targets. Questions:
>
>1. What is the frequency range and average amplitude of bat radar?
>
>2. What sort of microphone(s) would be best? If bat radar is fairly
>   low amplitude, should I build a parabolic mike? How does one properly
>   design a parabolic dish for a given freqency range? I probably don't
>   want to go for omnidirectional sensitivity anyway, since that would
>   make it impossible to track a single bat diving after an insect.
>
>3. What sort of frequency converter circuitry would I need?
>
>The ideal setup would be a small box containing the electronics and
>batteries with a jack for a pair of headphones to monitor the
>down-shifted signals and a jack for some sort of pistol-grip mounted
>mike that I could point at areas of interest.
>
>					Jordan Hubbard
>					jkh@meepmeep.pcs.com
>					Munich, West Germany
>			PCS Computer Systeme GmbH, Munich, West Germany
>	UUCP:		pyramid!pcsbst!jkh jkh@meepmeep.pcs.com
>	EUNET:		unido!pcsbst!jkh
>	ARPA:		jkh@violet.berkeley.edu or hubbard@decwrl.dec.com


This appeared here sometime ago, hope it helps.


From rex!ukma!tut.cis.ohio-state.edu!cs.utexas.edu!oakhill!charlie Wed May 10 16:52:49 CDT 1989
Article 557 of sci.electronics:
Path: mgse!rex!ukma!tut.cis.ohio-state.edu!cs.utexas.edu!oakhill!charlie
>From: charlie@oakhill.UUCP (Charlie Thompson)
Newsgroups: rec.ham-radio,sci.electronics
Subject: BATRADIO
Keywords: BATS
Message-ID: <2000@radio.oakhill.UUCP>
Date: 24 Apr 89 15:25:04 GMT
Organization: Motorola Inc. Austin, Tx
Lines: 40
Xref: mgse rec.ham-radio:1056 sci.electronics:557
Posted: Mon Apr 24 10:25:04 1989
Status: RO


This weekend I decided to scrounge through my junkbox and build
a BATRADIO.  I took a 25 Khz narrowband ultrasonic transducer
and preamp'd it and passed the amplified signal to a homebrew
direct conversion 25 KHz receiver.  The receiver was a homebrew
mixer and a Wavetek 111B (B as in battery powered). The output
of the mixer was lowpass filtered and sent a jambox for listening.
 
Austin has a rather unique downtown bat population that lives under
the Congress street bridge.  At sundown the bats begin stirring and
then, all at once, about 500,000 bats stop hanging around and start
flying in one giant cloud. Bazzare. The BATRADIO worked great and
I learned a lot about bat transmissions. 

Later, after the bats had left the bridge, I drove home and set up
the BATRADIO again.  I detected one lone bat, somewhere in the dark
chirping away. 
 
Bat transmissions are FM/AM.  That is, they are swept pulses, like
a chirp...which is what they sound like when you downconvert to
the 'human band'.  Sometimes the chirping is fast ... sometimes slow.
The bat on my street was chirping slowly until a car drove by and
it suddenly went to double the chip rate...presumably it had
'locked on' to the car.  When the car went away the bat resumed
chirping at the slower rate.  From what I could tell the bats
must have a 'deviation' of 5 to 10 KHz.  Since my receiver was
only about 2 KHz wide at 25 KHz I couldn't know exactly what the
deviation was.  The transducer that I used was resonant so it was
not very useful to tune my local oscillator since the sensitivity 
dropped off abruptly outside the range of the transducer's center
frequency. 
 
Anyway, it was an educational experience... and the best VLF'ing
I've done in a long time! Happy bat hunting.
 
-Charlie Thompson WB4HVD
 Austin, Texas


  


-- 
Mark Seiffert,  Metairie, LA.
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