49 lines
3.7 KiB
Plaintext
49 lines
3.7 KiB
Plaintext
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Phile 2 of 4 Audio Surveillance
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------------==========SANctuary===============------------------
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Audio is the most common surveillance method in use. Most listening devices depend on some form of electronics, and it is important to understand the
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usual steps to audio electronic surveillance. It is basically a 5 step process.
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1) Input- usually a microphone
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2) Preamplifier- used to boost the nominal signal of a mic to usable levels
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3) Processing- eliminates excess noise and unwanted sounds from the output
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4) Output- Headphones, recorder, transmitter, etc.
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5) Post-processing (sometimes)
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This phile will deal with preamplification. Preamplifiers boost the signal from the input to a usable level. Most microphones and sensors, such
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as phototransistors in light transmission bugs, give a signal that lacks power to do anything useful. The electricity generated by the needle of a
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record player can't drive the speakers of your stereo system.
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The main factors of preamplification are gain and noise. Gain is the increase in signal given by the preamplifier. Noise is unwanted sound that
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the preamp generates. A good preamp can make up for a mediocre mic or a bad signal due to the location of the target with relation to he mic, but
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nothing can compensate for a bad preamp. A good preamp has high gain and low noise. There is no limit to the amount of gain that can be applied, but
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noise and electrical breakdown limit the practical application of it. Noise increases with gain, so the limit is where noise overwhelmes the signal.
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Electrical breakdown occurs when gain is so high that inaudible ultrasonic feedback causd by the location of the components with relation to each
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other causes the preamp to shut down. Electrical breakdown also occurs when gain is so high that oscillation occurs and a squeal is sent through the
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mic or speaker. That can sometimes be lessened by shielding or changing the location of the mic.
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Operational amplifiers (op Amps) are often used because they are inexpensive, simple to use, easier to handle, and offer higher gain and lower
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noise than normal-component amplifiers. Op Amps are integrated circuits (ICs) that were originally developed for use in analog computers in the
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1940s. They are high performance linear amplifiers with 2 inputs, allowing for inverted and non-inverted output (negative and positive gain). The
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gain is determined by a resistor that feeds some of the amplified signal back to teh inverting input. The smaller the resistor, the lower the gain.
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An Op Amp amplifies the difference between the input and ground. This may seem complicated, but it actually makes amplifier design much simpler.
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Even a novice could design a simple amplifier using only the Op-amp's data sheet. It is important to keep the battery leads short, but most amps
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avoid that restriction by using a capacitor to keep the input from oscillating. Op Amps are the components that make miniature bugs posible.
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Well, I guess that'll do it for this phile. Watch for the rest of the series by,
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The Gaurdian!
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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+++++++++++++++++++++++ SANctuary +++++++++++++++++++++++++++++++++++
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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Oi! The Gaurdian is really moving quick with these survelence philes!
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Hope you enjoy them!!!
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Call the SANctuary WORLD HQ!!! HELLFIRE BBS!!! (908) 495-3926
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----===Red===----
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EAT THE RICH!!!
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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==========================SANctuary==================================
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-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-==--=-=-=-=-=-=-=-=-=--=--=-=-=-=
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