diy
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4 4 64 65 EYE SPY ISSUE 48 , 2007 EYE SPY ISSUE 48 , 2007 EYE SPY DIY SPYCRAFT DEGREE OF DIFFICULTY Eye Spy presents three DIY projects using a tape recorder that will allow you to make recordings only you can hear; devise a cheap through-wall listening device and make a parabolic microphone for hearing long distance sounds PROJECT ONE: LISTEN IMPOSSIBLE MAKE RECORDINGS ONLY YOU CAN HEAR FOR YOUR EARS ONLY ☺ TOUGH CONCENTRATE EASY aking private messages that stay private is not so easy in today’s digital world. Many people are now migrating from using M standard cassette tape recorders to newer digital format recorders such as MP3 and MP4. CDs have also lessened the popularity of the humble tape cassette - so much so that it’s feasible they will one day disappear altogether. Digital recorders are easy to use. They can record for hundreds of hours, and enable operators to make business notes, download and play music, or listen to the radio. However, the recorded or uploaded content in its raw state is accessible to anyone. Making audio notes on any digital recorder is open to abuse - and we don’t think there is any way of properly coding such information until it is removed from the device. This might be problematic if the recording contains compromising information, notes on a business transaction, or was made covertly using a hidden device. In this DIY feature, we find uses for both these types of recorders. However, if you want to make a recording only you can hear, then a standard tape recorder is, perhaps, the better option. For this project you will need a cassette recording machine (any cassette player - including the popular ‘Walkman’-size), a small jeweller’s-type screwdriver - those found in the common eyeglass fix-it kit, and a blank cassette tape. When a recording is made on a standard tape-recorder, the actual cassette tape is locked into position so that the thin recording tape moves past the Record/Play tape head at a constant 90 degree angle. This is called the tape head’s “azimuth angle”. The tape-head position can be adjusted by turning a small screw usually located a few millimetres away from this device - and usually accessible. If this is done, the quality of any pre- recorded tape, music, voice, story book etc. will suffer if played on this machine. Switched in play mode the tape head assembly jumps forward revealing the screw However, if a blank cassette tape is recorded on this machine, the quality will be fine - but only if it is played back on that particular recorder. Played back on a different machine, the sound will be garbled and incomprehensible. You can take advantage of this effect - called ‘azimuth loss’ - by recording messages on your recorder with the tape head position changed and then re-adjust the recorder in the normal fashion. If someone plays the tape in another recorder, the signal will be virtually inaudible. When needed, simply readjust the screw until the sound is back to normal. HOW-TO Since the screw that allows adjustment of the tape-head position is very small (sometimes cross- shaped), you will need a tiny screwdriver. These can be found in most pharmacy/drug stores in an eyeglass repair kit, for example. Cheap sets found on any market also include a couple of these screwdrivers. Look carefully at the tiny hole or slot on the case near the tape head. There is a small screw that allows you to adjust the head position. Turning the screw in either direction alters the azimuth angle. If you are not sure which screw to turn - check the user manual, ask an electrician, or just test them one by one. However, you should be able to identify the screw in a few seconds. It’s important to note the original position of the screw. Place a pre-recorded tape cassette in the tape recorder and press the PLAY button. The sound will already be effected. The sound quality decreases further as you turn the screw in either direction from its starting point. Leave the screw in the position that produces the lowest audio and quality level. Next, place a blank tape in the recorder and, with some music playing in the background (to make it more difficult for an eavesdropper to understand what is being said), press the record button and speak into the microphone. When you play back the tape, you’ll hear your voice clearly: but play the tape in another machine and you won’t. This is an old trick - probably originating from the early days of the Cold War. Those charged with acquiring audio intelligence, or carrying messages by cassette to colleagues used similar tricks. You can also conceal the “garbled message” in the middle of a pre- recorded tape, an album for example, for extra security. Recording tags on the upper left and right side of the cassette have been removed so you can’t accidentally tape over the music. A simple strip of clear tape positioned over these holes allows you to record over the music. Fast forward a few minutes and then change the azimuth angle and record your message. Anyone listening to the tape will think it has been damaged at that point - but a few moments later it will be “normal” and the music will return. PROJECT TWO: LIVE AND LET SPY MAKE A SOUND AMPLIFIER OR THROUGH- WALL LISTENING DEVICE rofessional ‘listen-through- wall’ machines are fairly pricey. A descent unit capable of penetrating a few inches can cost anywhere P between £200-£400 ($400-$800). More expensive LTW machines are available but can cost six or seven times that amount. These are exceptional, trade standard and often come with a multitude of features and in-built recording and transmitting devices. There is a very cheap solution that can replicate the results of low-end LTW machines. CONCEPT AND HISTORY As youngsters, one great trick performed with friends was to listen through a wall or door by placing a glass against its side. The results were always dependent on how thick the wall was, incidental background noise (on both sides of the wall), and the size and shape of the glass. At least two of these factors are important even when using quality LTW devices. However, by using an MP3 player or an ordinary The trick works with an ordinary tape recorder or an MP3 or 4 player What you will need: tape recorder, cassette, mini screwdriver ☺
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Switched in play mode the tape head assembly jumps forward revealing the screw What you will need: tape recorder, cassette, mini screwdriver The trick works with an ordinary tape recorder or an MP3 or 4 player DEGREE OF DIFFICULTY However, the recorded or uploaded content in its raw state is accessible to anyone. recording only you can hear, then a standard tape recorder is, perhaps, the better option. TOUGHCONCENTRATEEASY CONCEPT AND HISTORY HOW-TO
Transcript of diy
44
64 65E Y E S P Y I S S U E 4 8 , 2 0 0 7 E Y E S P Y I S S U E 4 8 , 2 0 0 7
EYE SPY DIYSPYCRAFT
DEGREE OF DIFFICULTY
Eye Spy presents three DIY projects using a tape recorder
that will allow you to make recordings only you can hear;
devise a cheap through-wall listening device and make a
parabolic microphone for hearing long distance sounds
PROJECT ONE: LISTEN IMPOSSIBLEMAKE RECORDINGS ONLY YOU CAN HEAR
FORYOUREARSONLY
☺ � �TOUGH CONCENTRATEEASY
aking private messagesthat stay private is not soeasy in today’s digitalworld. Many people arenow migrating from usingM
standard cassette tape recorders tonewer digital format recorders suchas MP3 and MP4. CDs have alsolessened the popularity of thehumble tape cassette - so much sothat it’s feasible they will one daydisappear altogether.
Digital recorders are easy to use.They can record for hundreds ofhours, and enable operators tomake business notes, download andplay music, or listen to the radio.
However, the recorded or uploadedcontent in its raw state is accessibleto anyone.
Making audio notes on any digitalrecorder is open to abuse - and wedon’t think there is any way ofproperly coding such informationuntil it is removed from the device.This might be problematic if therecording contains compromisinginformation, notes on a businesstransaction, or was made covertlyusing a hidden device.
In this DIY feature, we find uses forboth these types of recorders.However, if you want to make a
recording only you can hear, then astandard tape recorder is, perhaps,the better option.
For this project you will need acassette recording machine (anycassette player - including thepopular ‘Walkman’-size), a smalljeweller’s-type screwdriver - thosefound in the common eyeglass fix-itkit, and a blank cassette tape.
When a recording is made on astandard tape-recorder, the actualcassette tape is locked into positionso that the thin recording tapemoves past the Record/Play tapehead at a constant 90 degree angle.This is called the tape head’s“azimuth angle”. The tape-headposition can be adjusted by turninga small screw usually located a fewmillimetres away from this device -and usually accessible. If this isdone, the quality of any pre-recorded tape, music, voice, storybook etc. will suffer if played on thismachine.
Switched in play mode the tape head assemblyjumps forward revealing the screw
However, if a blank cassette tape isrecorded on this machine, thequality will be fine - but only if it isplayed back on that particularrecorder. Played back on a differentmachine, the sound will be garbledand incomprehensible.
You can take advantage of thiseffect - called ‘azimuth loss’ - byrecording messages on yourrecorder with the tape head position
changed and then re-adjust therecorder in the normal fashion. Ifsomeone plays the tape in anotherrecorder, the signal will be virtuallyinaudible. When needed, simplyreadjust the screw until the sound isback to normal.
HOW-TO
Since the screw that allowsadjustment of the tape-head positionis very small (sometimes cross-shaped), you will need a tinyscrewdriver. These can be found inmost pharmacy/drug stores in aneyeglass repair kit, for example.Cheap sets found on any marketalso include a couple of thesescrewdrivers.
Look carefully at the tiny hole or sloton the case near the tape head.There is a small screw that allowsyou to adjust the head position.Turning the screw in either directionalters the azimuth angle. If you arenot sure which screw to turn -check the user manual, ask anelectrician, or just test them one byone. However, you should be able toidentify the screw in a few seconds.It’s important to note the originalposition of the screw.
Place a pre-recorded tape cassettein the tape recorder and press thePLAY button. The sound will alreadybe effected. The sound qualitydecreases further as you turn the
screw in either direction from itsstarting point. Leave the screw inthe position that produces thelowest audio and quality level.
Next, place a blank tape in therecorder and, with some musicplaying in the background (to makeit more difficult for an eavesdropperto understand what is being said),press the record button and speakinto the microphone. When you playback the tape, you’ll hear your voiceclearly: but play the tape in anothermachine and you won’t.
This is an old trick - probablyoriginating from the early days ofthe Cold War. Those charged withacquiring audio intelligence, orcarrying messages by cassette tocolleagues used similar tricks. Youcan also conceal the “garbledmessage” in the middle of a pre-recorded tape, an album forexample, for extra security.Recording tags on the upper left andright side of the cassette have beenremoved so you can’t accidentallytape over the music. A simple stripof clear tape positioned over theseholes allows you to record over themusic. Fast forward a few minutesand then change the azimuth angleand record your message. Anyonelistening to the tape will think it hasbeen damaged at that point - but afew moments later it will be“normal” and the music will return.
PROJECT TWO: LIVE AND LET SPYMAKE A SOUND AMPLIFIER OR THROUGH-
WALL LISTENING DEVICE
rofessional ‘listen-through-wall’ machines are fairlypricey. A descent unitcapable of penetrating a fewinches can cost anywhereP
between £200-£400 ($400-$800).More expensive LTW machines areavailable but can cost six or seventimes that amount. These areexceptional, trade standard andoften come with a multitude offeatures and in-built recording andtransmitting devices. There is a verycheap solution that can replicate theresults of low-end LTW machines.
CONCEPT AND HISTORY
As youngsters, one great trickperformed with friends was to listenthrough a wall or door by placing aglass against its side. The resultswere always dependent on how thickthe wall was, incidental backgroundnoise (on both sides of the wall), andthe size and shape of the glass. Atleast two of these factors areimportant even when using qualityLTW devices. However, by using anMP3 player or an ordinary
The trick works withan ordinary tape
recorder or an MP3or 4 player
What you willneed: taperecorder,
cassette, miniscrewdriver
☺
