# Detecting Ultrasound

P

#### [email protected]

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

M

#### martin griffith

Jan 1, 1970
0
On 10 Mar 2007 05:18:34 -0800, in sci.electronics.design
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!
http://pw1.netcom.com/~t-rex/BatDetector.html may work

martin

C

#### chuck

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

Interesting.

The mixing process requires a non-linear device, which, for your
purposes, I suspect the air is not. I've often considered, but never
attempted, a similar mixing process using human ears (connected and
intact, of course), since ears are quite non-linear. Ears won't work as
mixers in your case since, at least for most adults, they are
insensitive to ultrasonic frequencies (as well as to intelligent
political analysis, it seems).

The suggested bat detector is far more promising.

Chuck

P

#### PeterD

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

Why worry about it... His yard, his pets, his life...

OK,

Take a microphone with a frequency response > 30Khz, and an amplifer.
Monitor the amp's output with a scope. <bg>

S

#### Stace MacGuyver

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

Suspend a thin shaving razor blade between two pieces of dental floss and put

J

Jan 1, 1970
0
C

#### clifto

Jan 1, 1970
0
Stace said:
Suspend a thin shaving razor blade between two pieces of dental floss and put

That's pretty cool, MacGuyver. Does the razor blade do anything?

S

#### Scott

Jan 1, 1970
0
It cuts off your ear if you get too close

L

#### [email protected]

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

The obvious "detection" would be oscilloscope observation
of the amplified microphone signal. That's been mentioned.

Some commercial ultrasound detectors simply heterodyne
the ultrasonic range down to audible frequencies...good if
your hearing goes on up to the high end of human response.
Expensive as portable devices but easily genned up on the
average home workbench.

There are a couple of claims of outdoor advertising via sound
through using high-power ultrasound generators in pairs, one
modulated in amplitude the other unmodulated. The air acts
as the non-linear "mixer" and the claim is that such beams
of ultrasound can be focussed on particular locations. One
such company is located in San Diego, California, if memory
serves.

73, Len AF6AY

J

#### John Smith I

Jan 1, 1970
0
Scott said:
It cuts off your ear if you get too close

Be better if you could use it as an electric razor ...

JS

C

#### Chris Jones

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned wonÂ´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, whatÂ´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. IÂ´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

To get the air to be non-linear enough to mix the two frequencies, you would
need very high sound pressure levels that could potentially be hazardous
(or at least much more of a nuisance that whatever your neighbour is
doing). I would suggest getting a wideband microphone (a very small
electret might do, and would be less high-Q than a typical ultrasonic
transducer), and then attach a preamplifier and an electronic mixer with an
adjustable local oscillator (e.g. make a bridge from switches using a 4066
or FST3125 that alternately inverts or doesn't invert the signal). The
output of the mixer can be fed to an audio amplifier and headphones. You
can then test this receiver if you buy or borrow one of those cheap "pest
annoyer" things. Once you know that your receiver works, you could make a
parabolic reflector (e.g. spin cast a dish on an old record player from
plaster of paris in a bin lid), so that you can search for sources of
ultrasound.

Chris

C

#### clifto

Jan 1, 1970
0
John said:
Be better if you could use it as an electric razor ...

Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
all throughout the spectrum. What's the resonant frequency of a whisker?

M

#### [email protected]

Jan 1, 1970
0
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. Id
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

You need your detector to be low Q since you don't know the offending
frequency. Some of these fancy sound cards do 196kHz sampling. A
piezo microphone with amp into the sound card might do the trick.

Also, as other have suggest, the bat detector.

J

#### John Smith I

Jan 1, 1970
0

Do you really want to hear it, or have a "field strength indicator"/locater?

Why not just a mike capable of "hearing" the ultrasonic freqs in
question--feeding an opamp and meter?

Pointing the mike around should lead you into the correct direction and

Possibly can substitute a light or even a led in series with a pot and
use a visual indication of strength ...

JS

J

#### John Smith I

Jan 1, 1970
0
John said:
Do you really want to hear it, or have a "field strength
indicator"/locater?

Why not just a mike capable of "hearing" the ultrasonic freqs in
question--feeding an opamp and meter?

Pointing the mike around should lead you into the correct direction and

Possibly can substitute a light or even a led in series with a pot and
use a visual indication of strength ...

JS

Come to think of it, wouldn't take much more to square up the sine wave
out of the opam and drop a cmos decade-divider onto that output of the
opamp and feed an ear phone with the dividers output--30,000 becomes
3,000 hz--easily "hear-able!"

JS

J

#### jasen

Jan 1, 1970
0
Come to think of it, wouldn't take much more to square up the sine wave
out of the opam and drop a cmos decade-divider onto that output of the
opamp and feed an ear phone with the dividers output--30,000 becomes
3,000 hz--easily "hear-able!"

only if theres no other sound present in the mic signal.

and it will give no indication of signal amplitude.

D

#### Doug Smith

Jan 1, 1970
0
Why worry about it... His yard, his pets, his life...

I *think* what the OP is worried about is that his friends' pets are being
scared off by his freinds' neighbor.

While I hate to discourage anyone from building something electronic, I do
have to ask: what will one do if they learn that a bird-scarer *is* in
use? Best of my knowledge, they aren't illegal.

If a bird-scarer works on dogs, then I find the details quite interesting.
May have to work up a mobile version. Loose dogs allowed to roam a
neighborhood are a serious safety issue for cyclists. (and I wonder if
that's why the neighbor in question is trying to scare them off?)

M

#### Michael A. Terrell

Jan 1, 1970
0
clifto said:
Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
all throughout the spectrum. What's the resonant frequency of a whisker?

They don't make the blue blades anymore.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

M

#### Michael A. Terrell

Jan 1, 1970
0
clifto said:
Do they make any other kind of thin shaving razor blades?

Yes, but the blueing was what made a detector.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

R

#### Rich Grise

Jan 1, 1970
0
I don't know how your sense organs are arranged, but I know that if I
dangle something next to my ear, it's terribly hard to watch it
simultaneously. ;-)

Yes, but the blueing was what made a detector.

What does that have to do with dangling the blade from dental floss? Or,
for that matter, what does dangling a blade from dental floss even DO?

Thanks,
RIch

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