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Date: Tue, 06 Mar 2007 21:53:46 -0500
To: "TSCM-L Professionals List" <TSCM-..._at_googlegroups.com>
From: "James M. Atkinson" <jm..._at_tscm.com>
Subject: Re: [TSCM-L] Ultrasound translators..any uses in tscm ?
In-Reply-To: <1172801603.109668.102050_at_b35g2000cwb.googlegroups.com>
References: <1172801603.109668.102050_at_b35g2000cwb.googlegroups.com>
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Be patient when you ask a question, some of us
are older and have to mull over the question and
then organize a committee before an answer can be
given, the questions can then be tabled to the
committee and opened for discussion following
Robert's Rules of Order, etc, etc, etc.
What was your question again?
Just kidding, I have busier then a two headed dog
in a room full of cats recently.
Anyway, to your question and the matter at hand:
Are you seeking to detect a mechanical or audio
pressure wave, or are you seeking to detect
magnetic wave, electrical waves, of a combination
of electro-magnetic waves. This is quite
important as the design of a purely magnetic
pickup is going to be significantly different
then a mechanical unit which is going to be
different then one that will respond to EM.
By example, if you seek to detect 15 kHz or
15.734 kHz base-band video signals you will want
to shield the antenna against electrical signals
by shielding the loop with aluminum, if on the
otherhand you seek to pickup only the electrical
component then you will want to shield with a
high nickle/cobalt/copper alloy. Now on the other
hand if you are seeking to pickup the mechanical
energy only then you will need a mechanical
transducer of pickup to convert the movement to
an electrical signal you can do something with.
The first step is to define what you are seeking
to collect and optimize the pickup, but reject
the unwanted signals. After this it becomes a
virtually identical circuit for amplification
filtering, and detection purposes, but based on
my own experience I can strong recommend that you
give a lot of though on how you will be shielding
the detector, and the environment in which you will be using it.
Most modern recorders operate with a 32.76 kHz
oscillator, and the second harmonic (of first
harmonic is you want to be picky) of a modern
composite video signal of either 30 kHz or 31.468
(2x 15 or 15.734 kHz), so the first segment of
the spectrum you need to ponder is the 30-33 kHz
area as you will find more there of value relative to our business then not.
If you add a fixed capacitor, and a small value
varistor diode you can shoot a little DC up the
antenna cable to tune the antenna remotely, with
a ten turn potentiometer. You can then feed the
DC in the form of a low frequency saw tooth
wave-form so that you can bring the loop to
resonance anywhere over the frequencies of interest.
I take this a step further where I use the X-Axis
of my spectrum analyzers as a tuning voltage for
the antenna varactor. Instead of using string
theory, calculus, and black magic to make the
antenna to submit to the spectrum analyzer I
instead let the tell the spectrum analyzer how
the antenna will behave given a particular
X-voltage, and the range of frequencies tuned
relative to the X-voltage of tuning and I set the
X-Axis of the SA up to that frequency.
Lets look at this a bit more. I set my spectrum
analyzer to a center frequency of 31.5 kHz, and
set my span from 30 to 33 kHz for a window that
is only 3 kHz wide. I then construct a ultra high
permeability loop stick antenna that is perfectly
resonant dead on 31.5 kHz (trust me, it is quite
possible to do this). This is all well and good,
but what is I want to look slightly above, and
slightly below 31.5 kHz, well then I have to put
a capacitor across the antenna, and if I intend
to remotely tune the antenna it needs to be a
capacitor with a capacitance which I can remotely
increase or decrease (and hence remotely tune the
antenna). We can either throw a needlessly
complex solution at the problem involving remote
control tuning arrays, computer interfaces,
switched filters, or we can have a plan B.
The spectrum analyzer I am using for this example
has a sweep voltage of 10 volts in then when the
sweep is at the center frequency the voltage is 5
volts, and when it is at the far end of the SA
display the voltage is 0 and 10 volts
respectively. Plan B in this case is to "add
biasing capacitor to the antenna to that when it
is O volts the capacitance of the varactor is
such that it is resonating the antenna just a
hair below 30 kHz, and that with 10 volts it
resonants just a hair above 33 kHz. So we make
the spectrum analyser submissive to the antenna,
and not the other way around. The SA sets the
sweep frequency to 30 kHz and creates a 0 VDC
signal to the varistor on the antenna, and as the
sweep begins the voltage increases on the X-Axis,
which increases the capacitance of the varistor
which in turn changes the resonance of the
antenna. If you adjust the span displayed on the
SA screen you can obtain a perfect tuning match with this method.
In the case of a receiver, you do something
similar and feed the tuning voltage as a free
running oscillator, or throw a switch and manually tune the antenna remotely.
Many IED use a digital watch of timing device
that can be very easily rejected with a very
simple project called a boom-stick (tm) which
contains a special alloy core, and a electronic
shield on one end and a detection circuit/alarm
on the other end. The alloy core is wrapped with
very fine copper wire loop, and the secured in a
silicone and gell cushion as the alloy is quite
brittle.The stick is "calibrated" by placing it 3
feet above any digital wrist watch, and then
turning a sapphire piston capacitor to get a peak
reading on the readout column (the sapphire
piston actually tuned the loop to the high end of
the scale). The stick has a 90 dB scale so you
move it 18 inches away, mark it on the stick
display, move it another 18 inches and so on
until only the lowest LED is illuminated. One of
these sticks will detect a digital wrist watch a
solid 50 feet away, through concrete walls to
detect IED's hidden in a room, and other nefarious items.
Now, it you are more interested in detecting a
mechanical watch, or and older style video
camera, then you can use a standard Ultrasonic
stethoscope such as the Kaiser 2047 U/C.
-jma
At 09:13 PM 3/1/2007, cont..._at_yahoo.co.uk wrote:
>.
>
>I´m making my own bugdetector
>and playing with the idea of incorperating an Ultrasound-Translator.
>
>Ultrasound would be sound with frequencies above those that we can
>hear
>....lets say above 16 khz....up to maybe 60 or 100 kz.
>
>The translator or converter ...would translate ultrasound
>to audible frequencies.
>
>It would be fairly easy to build such a converter.
>
>
>Question
>------------
>
>Anyone have any ideas of the usefullness of something like that
>ofcourse related to countersurveillance or similar activities.
>
>There seems to be a few things that you could hear then
>things you would not be able to hear without such converter
>...just wich of them are usefull for us.
>
>Maybe i could here some transformers (inside electronic units)
>Video-monitors ? (not very usefull since usually these are not hidden)
>Oscillators ? ( as part from what kind of units ?...up to 100Khz ?)
>Alarmsystems ? (only usefull for "Watergate-teams" : ) : )
>Taperecorders (a little oldfashioned these days)
>VLF signals ?
>Maybe i could hear other things that point to bugging or related
>stuff ?
>
>Maybe someone discovers something new ?
>Up to what frequency ?
>
>Or just a scientific gadget ?
>
>All i know that it might be usefull for IED purposes..but thats not
>my kind of thing.
>
>
>Any ideas ?
>
>Thanks !
>
>contranl
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----------------------------------------------------------------------------------------------------
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Granite Island Group Fax: (978) 546-9467
127 Eastern Avenue #291 Web:
http://www.tscm.com/
Gloucester, MA 01931-8008 E-mail: mailto:jm..._at_tscm.com
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Received on Sat Mar 02 2024 - 00:57:28 CST