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Music Media

Generate AM Radio Broadcasts With Your Monitor 328

tessellation writes: "Tempest for Eliza is a program that uses your computer monitor to send out AM radio signals. You can then hear computer generated music in your radio." Here is your big chance to disrupt free thinking radio programs in your neighborhood.
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Generate AM Radio Broadcasts With Your Monitor

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  • Done it... (Score:3, Interesting)

    by Kymermosst ( 33885 ) on Tuesday November 27, 2001 @02:21AM (#2618038) Journal

    It really worked... it took more work than the instructions portrayed to get it working, but it's pretty nifty.

    Can't do MP3s yet... at least, not the version I tried.

    first post?

    • How far away can you hear it?
      • Re:Done it... (Score:3, Informative)

        by Kymermosst ( 33885 )
        With a crappy radio, it had to be fairly close 5 feet to make it out... my monitor doesn't put out that much rf... it's a low-rad type.

        Now, putting my ham radio at 5 watts about 10 feet away does interesting things to my monitor, I can tell you that!
        • I remember getting the same crappy performance from a $20 Radio Shack AM Broadcasting kit back in '77.

          It figures that I had to wait 25 years to be able to do the same thing with $1000 worth of computer hardware.

          Still, I wonder if I can use this technique to calibrate an HF tranceiver.

  • by ddent ( 166525 ) on Tuesday November 27, 2001 @02:23AM (#2618043) Homepage
    I wonder if it has something to do with how thin my monitor is... now wait a second, does this work on LCDs? :) Oh, maybe thats why...
    • But I've been in one of Ross Andersons lectures where him and Markus demonstrated tempest working against a laptop. Just using LCD won't protect you, see Here [] (google cache - page seems to be missing) and Here []
    • by Anonymous Coward
      Ah, but it _is_ working. It's not your monitor that is emitting the signal - it's the cable between your computer and the monitor.
      Be afraid, big brother is watching you :-)
  • by stonecoldt ( 525628 ) on Tuesday November 27, 2001 @02:31AM (#2618056)
    .ogg files would sound so much better out of that AM radio. :-P
  • This isn't the first (Score:5, Informative)

    by recursiv ( 324497 ) on Tuesday November 27, 2001 @02:35AM (#2618061) Homepage Journal
    This isn't the first time something like this has appeared on slashdot. Way back in the day ('99) there was an article [] about a guy who was using the radio interference from his motherboard to do the same sort of thing.
  • by ynotds ( 318243 ) on Tuesday November 27, 2001 @02:36AM (#2618064) Homepage Journal
    This is really testing my memory, but I think it was after we upgraded from our IBM 1440 to an early System/360 that our operators discovered they could tune an AM radio to a certain frequency and thereby listen to the puter.

    Maybe somebody with a better memory might know a few more details.
    • by Florian Weimer ( 88405 ) <> on Tuesday November 27, 2001 @05:50AM (#2618392) Homepage
      Our local computer museum has got a PDP-8 which can broadcast polyphonic music using its main CPU, running a specially crafted sequences of instructions. Actually, operators used the AM radio effect to monitor the machine activity. With some experience, you can here if the CPU is idle or spinning in some kind of endless loop. If you are familiar with a longer job, you can guess which part is currently running, and estimate the remaining time.

      At home, my computer has a similar feature: if the CPU is loaded, the sound of the fans changes, so I can tell if the computing-intense job is still running or not.
      • I have a vague recollection of reading about something like this in an old IEEE Annals of the History of Computing an article on EDSAC, the first stored program general purpose computer (ca. 1950, used mercury delay lines to store data acoustically). They used a radio to listen to the interference generated by the computer; a crash sounded different from normal operations. I believe this was not uncommon in the days of behemoth computers and no government emissions regs.
        • About 1965 Richard Smiley, a student at Carleton College in Minnesota, wrote a program that could play music (sort of) on an IBM 1620. You could listen to it on an AM radio placed near the machine. The 1620 was a variable word length machine, and the word length affected the time it would take to accomplish a task, thus changing the radio signal. Smiley exploited this variation to generate musical tones. IBM included this in the contributed program library that was available to all 1620 users.
  • this reminds me... (Score:3, Interesting)

    by anotherone ( 132088 ) on Tuesday November 27, 2001 @02:36AM (#2618065)
    This reminds me of a game I used to have for my TI-82. As I recall it was a dumb game, but it was the first (and as far as I know, the only) calculator game with music.

    I think it worked by twiggling the link port's connection really fast or something, but if you held it near an untuned radio, it'd play really poor music. Really, really bad music. But, hey; what do you expect from a damn calculator?

    Anyway, this is one of those completly useless, yet incredibly cool things that I like to see. Very neat.

    • by FuegoFuerte ( 247200 ) on Tuesday November 27, 2001 @02:47AM (#2618091)
      Actually, quite a few of the games for the TI-86 have music. Mario does, and I believe Tetris does also. (at least the versions I had). I've since gone to the TI-92+, and haven't tried it with that. On the 86, I heard rumors that you could tune it with an AM radio, but you could also plug headphones straight into the data port (with an adapter to go from the 2mm to the 3mm plug) and hear the sound great. Someone actually wrote a program to play music that way, though you can't fit much music into the memory on the 86. Pretty crappy quality too. You can probably still find the programs and info on or somewhere. It's been a couple years, so I don't remember where I first found out about it.
    • Back when the Hp-48G or GX was new, there were lots of games released with music...
    • Floppy Drive Music (Score:2, Interesting)

      by kotku ( 249450 )
      A guy at school years ago used to get his kicks by getting various computer peripherals to play music. The best was a 5 1/4 " floppy drive playing yankee doodle dandy. I think he just drove the head on the drive back and forwards in time with a sound input file. Dot matrix printers could also pump out a pretty tune.

      Unfortunately I know longer know this person and a cursory google search turned up nothing on floppy drive music. If anybody has a program to do the same then please post. I don't recommend running this on your own computer though :)
      • The BBC Micro had a built-in UHF-PAL output so you could view the display on your television. But it didn't include sound; that came out of the computer's built-in speaker. If you did turn the volume up on your TV you'd just hear noise, presumably it was caused as a byproduct of the picture generation and nobody bothered to filter it out. I remember generating lots of different buzzes and sqeaks from the television by poking random bytes into the video controller's registers and turning up the TV volume.

        I also read that the Sinclair ZX80 - a machine with no sound hardware whatsoever - could be made to play notes. There was a program listing in some magazine (ZX User, I think) to do it. Not having a ZX80 (the predecessor to the ZX81) I couldn't try it out, and I never checked whether the magazine's date was April.
  • Eliza? (Score:3, Funny)

    by the Atomic Rabbit ( 200041 ) on Tuesday November 27, 2001 @02:38AM (#2618067)
    Huh? Does the program use your monitor to produce a radio program about psychotherapy? How do you describe your problems to it?
    • Re:Eliza? (Score:5, Funny)

      by x136 ( 513282 ) on Tuesday November 27, 2001 @04:02AM (#2618234) Homepage
      ]Hello Eliza.
      ]I don't feel very good.
      Why is it that you don't feel very good?
      ]Well, my monitor is talking to my radio.
      Are you concerned about your monitor talking to your radio?
      ]Well, yes. It's not supposed to work that way.
      Why isn't it supposed to work that way?
      ]Shut up Eliza.
      Why do you want me to shut up?
      ]Because you are a stupid worthless computer program.
      I sense much anger in you. Perhaps you should seek medical help.
      ]Oh, what do you know?
      What is it about what I know that interests you?
      I don't understand what you mean by ARRRRRRGGGHHH!!!. Please try again.
      OK. Goodbye.
  • Van Eck phreaking (Score:5, Informative)

    by jasonzzz ( 415795 ) on Tuesday November 27, 2001 @02:38AM (#2618068) Homepage

    For many years during the cold war, the NSA had
    been nervous about natural radiations emanating/broadcasted by VDTs and electrical wiring. So much so that many government sites were constructed with TEMPEST safeguards with thick concrete walls, wiremesh shielding and isolated electrical works. Even then, VDTs, type writers, phones, and other electrical devices were never placed close to walls adjacent to the outside of the enclosed space.

    Read the Van Eck document.

    Read the TEMPEST page
  • legality? (Score:2, Interesting)

    by rootofevil ( 188401 )
    Doesnt every piece of electronic equiptment i own have that little FCC sticker that says it must accept any undesired interference, but not cause any of its own? wouldnt this fall under that exact category?
    • Re:legality? (Score:2, Interesting)

      by ocelotbob ( 173602 )
      This is perfectly legal. All electronic equipment is spec'ed to a certain amount of interference it can radiate. What this hack is working on is the fact that a monitor should be sending out a pretty fixed frequency that can be picked up by an AM radio, similar to how you can hear a repetitive beeping sound if you hold a remote next to an AM receiver in just the right spot. The FCC doesn't care because unless you do some heavy tweaking to your monitor, this isn't going to affect more than the 10-15 foot radius a monitor would normally slightly affect. You're allowed to microbroadcast that amount of distance.
      • Why would I hear beeping over AM on a remote? They are all infrared (and the original ones were ultrasonic). I've never heard of an RF remote...
        • Re:Beeping remote? (Score:2, Informative)

          by ocelotbob ( 173602 )
          Yes, I know most remotes are IR. However, the phenomena I'm talking about is fairly well documented; there are several faqs floating around on the internet discussing the subject. Because of how AM radios work, any localized source of radiation of sufficient strength, no matter what the frequency, will cause interference. Its similar to how a thunderstorm will cause pops when listening to the radio.
    • On a related note, be sure to check out the FCC-ID Number Search [] page. I used it to find out my Logitech Cordless mouse operates on 27.045MHz. Could be great for van Ecking arbitrary devices.
  • kernel? (Score:4, Funny)

    by ameoba ( 173803 ) on Tuesday November 27, 2001 @02:44AM (#2618082)
    Considering that the 2.5 kernel development cycle hasn't begun yet, is there still time to get the Monitro Sound device driver put in?
  • by elizard2k ( 532787 ) <> on Tuesday November 27, 2001 @02:49AM (#2618095) Homepage
    This is your chance to send out the many subliminal messages to the poor listeners at your work/neighborhood. *snicker*

    *crackle* this program has been interrupted by your next door geek .. buy him computer parts *crackle*
  • by swagr ( 244747 ) on Tuesday November 27, 2001 @02:52AM (#2618101) Homepage
    Put an AM tuner near your box, and you'll easily find a frequency (many in fact) that let you hear your PC.

    Type some keys... move your mouse, open a window...

    Not only are you broadcasting... you're composing...
  • "All your base are belong to us!"
  • FWIW (Score:5, Interesting)

    by adolf ( 21054 ) <> on Tuesday November 27, 2001 @02:55AM (#2618109) Journal
    While the instructions say to use a shortwave radio tuned to 10MHz, I found that a regular broadcast-band AM radio worked fine. Just chop a zero off of the frequency, and tune in somewhere around 1000. (1030 was what my tuner said, at the point where the "music" was most plainly heard).

    Spooky stuff, this.
    • at 1000 KHz you are listening to a harmonic of the 10MHz frequency. Same signal, less amplitude.
  • Wireless LAN (Score:2, Interesting)

    by cra ( 172225 )
    So, basically, by hooking up some old AM radios ("slightly" modified, of course) to every computer in my home, and by installing some sofisticated software (Will I need a "slightly" upgraded version of the mentioned software, I wonder?), I can actually have a wireless LAN in my home, right?
  • This is first time I am sorry I have a laptop!
  • by dhanav ( 313625 ) on Tuesday November 27, 2001 @03:03AM (#2618130) Journal
    Code a picture that will produce a voice and we have an encrypted speech. Sounds interesting. I am going to display all those pics in my collection and listen for hidden messages :).
  • by foqn1bo ( 519064 ) on Tuesday November 27, 2001 @03:14AM (#2618151)

    I recall hearing something once about the homebrew computer club @ Cal back in the 70's doing something like this using an Altair and a radio to play The Beatles' classic, "Fool on the Hill". It was judged the most interesting and useful thing anyone had managed to do with an Altair yet. I am glad that over 20 years later programmers are dedicated to making our computers just as useful and practical.

    • IIRC, the first time this modulated RF interference was used to create music utilized the services of a PDP-7. (Was there such a machine? It was a PDP-something, at any rate.) There was a demonstration using an Altair at a homebrew meeting, although I think it played something like "Greensleeves". Definitely not The Beatles, tho'.

      BTW, if you want to find out about probably the first ever attempt to make music with a computer (although it didn't utilize this technique), check out the music of CSIRAC [].

      • by hawk ( 1151 )
        Yes, there was such a beast. And the PDP-6, which was the predecessor to the 10. PDP 1-11 were all designed, but not all were built.

        However, these are still later than the playing of such tunes on mainframes in the 60s


    • I recall hearing something once about the homebrew computer club @ Cal back in the 70's doing something like this using an Altair and a radio to play The Beatles' classic, "Fool on the Hill".

      And if they did it today, they'd get sued by the RIAA. :)
    • There was a similar program for the Radio Shack Model I. It worked using basic Language loops called as subroutines (GOSUB statement). Each loop was slightly different, producing a different tone on the radio.. The loop count variable determined how long the loop ran for. It was called a jukebox because there was a whole menu of tunes you could play with it.
  • by dido ( 9125 ) < minus poet> on Tuesday November 27, 2001 @03:16AM (#2618153)

    Well, it didn't immediately click because the Beethoven song he used to test the program is better known by its German name: "Für Elise" (well, that's what the book of piano pieces I used to have calls that tune). Trouble is, everyone's associations to the name 'Eliza' is the 'AI' program by Joseph Weizenbaum...

  • Geek history (Score:2, Interesting)

    by pacc ( 163090 )
    It all began somewhere in California when a student didn't think that pulling a few switches to get a few red lamps to produce the answer was good enough.

    With a bit of experimentation he produced a program that did nothing, but when he tuned in the radio next to the old monster a small tune was heard when his program was run.

    Other Examples: One of the highlights of our open day display was a music program running on the DS300. This machine has no loudspeaker - the four-part harmonies are picked up by an AM radio tuned to the rf interference generated by the core driver circuits. For best results, pull your PDP-8 processor cabinet right out and place the radio immediately above the core stack.
    Resurrection, some kind of antique computer society []

    Can't find the correct reference, try yourself to search the net for computer, music etc
  • I programmed an Imlac [] and used to get audible sound out of the monitor when my lines got redrawn too fast. I always thought it was going to blow up.
    • I recall hearing tales in the 80s of a trojan that would cycle the horizontal and/or vertical hold so fast that some cheapo monitors would actually explode. Not sure if there was any truth to it or not.

      • There was a POKE for a particular model of Commodore PET which would kill the monitor.
        Can't remember what it was, but I'm sure someone out there will...!
        • Re:Only Radio? (Score:2, Informative)

          by jacklf ( 214580 )
          Since you brought it up... [from the CBM-PET FAQ []]:


          This is THE POKE of computer lore, the command that WILL physically break a
          computer! Of course other commands and methods are known that can
          potentially cause damage (usually to disks, hard drives or other mechanical
          units), but this is the most notable mainly because it was a command somewhat
          commonly used and it affects solid-state circuitry.

          History of 'the killer poke'
          When the first PETs (small 9" screen) models came out, the display wasnt all
          that fast.

          The old PETs were slow because the print character ROM routine
          waited for the interval between screen scans before updating the screen
          memory. This reduced conflicts over the screen RAM which would have resulted
          in random pixels (snow) being illuminated on the screen. There was an input
          on one of the I/O chips which was hooked up to the video circuitry and told
          the routine when to access the video RAM.

          It wasn't too long before someone learned they could impove the
          character display speed via a poke to location 59458; which would set the
          video controller to update more readily. It was a noticible improvement of
          speed on programs using PRINT often, it was kind of like a free upgrade.
          It was mentioned in a few publications and used in many programs that relied
          on printing to the screen. I had learned of the poke through Cursor Magazine,
          a monthly tape-based publication. They printed the command in one of the
          'newsletter' flyers included with an issue which you could insert into their
          game "joust" to make it play faster.

          Later on, when Commodore released the larger display (14") PETs, they had
          improved the display controller which made that POKE unnecessary. An
          unfortunate side effect was that the POKE to 59458 affected a different
          register which adjusts one of the newer screen display capabilities, which
          could result in damaging the PETs video curcuitry when left running. I
          discovered it by accident after our school received some large-screen 4016s.
          When active, the screen starts to warp after about the third line and the
          display stops around the fifth, the keyboard is also unresponsive. When a PET
          is in this mode, the only solution is to turn it off, FAST! Fortunately none
          of the school's PETs were damaged due to this POKE. Later Cursor Magazine
          published a 'fix' that would allow older PETs to use the poke and keep the
          large-screen units from frying. Unfortunately there are still many programs
          that do not have this fix.
  • Legal issues (Score:2, Interesting)

    by Pat__ ( 26992 )
    I don't know the range of this thing :)
    But correct me if I am wrong ... Isn't it illegal to broadcast on AM frequencies without a licence in most parts of the world?
    • Re:Legal issues (Score:4, Informative)

      by dattaway ( 3088 ) on Tuesday November 27, 2001 @10:30AM (#2619061) Homepage Journal
      Oh, there are a few ways to increase the output of your monitor by many watts too. These require the case to be taken off and willingness to turn your screwdriver on parts connected to the B+ chassis (about 2000 volts.) Uplugging the computer during this process is optional. Voiding your monitor's warranty and making it a potential fire hazard is your destiny with this procedure.

      Brightness is one good way. Want to vaporize some phosphor off the screen? Well, look at that funny transformer with the thick red wire going to the picture tube's top. No, don't put your fingers under that red cap as you'll discharge 30,000 volts. The capacitance stores enough current that it may jump start your heart into transporter mode to a higher (or lower) place in the heavens. Anyways, look back on the transformer where one or two or more small screwdriver adjustments are provided. One should be the focusing voltage for the electron voltage. All this adjustment will do is make your picture tube require prescription glasses when things get fuzzy. The other adjustment dangerously raises the drive voltages of your homebrew particle accelerator into x-ray producing levels. Enjoy.

      The other tasty method to injure personal health is to max out horizontal drive voltage. Your adjustment of choice is on the main circuit board that is a minefield of tempting adjustments. The one I am talking about is an adjustable inductor, when tinkered with will lose the monitor's calibration for the horizontal picture width. Its the one adjustable inductor that stands taller than the rest and its frequency is so high, its design require the turns of wire to be a bundle of stranded wire. Yes, remove the powdered ferrite slug out of this coil. Current will now saturate the picture tube's yoke coils. Electronic devices and radios around the house will now bow to your monitor's new elite status.

      There you go. Not only have you voided your monitor's warranty, you have just demonstrated why picture tubes are evil particle accelerators. They should be banned.
      • Re:Legal issues (Score:2, Interesting)

        by Tycho ( 11893 )
        Don't tempt me. Also to produce X-rays like that you would somehow have to defeat the X-ray protection circuit. Not impossible just harder to do. Another great thing to concentrate those X-rays would be to unplug or remove the vertical and horizontal deflection coils and fix some of the other components so there is no more vertical or horizintal deflection that occurs in the monitor. The electron beam would then come out as a point on the screen. Which would be great fun as long as you were at least a half mile away when you turned the monitor on.
  • by Chmarr ( 18662 ) on Tuesday November 27, 2001 @04:07AM (#2618245)
    Eh... old news. My TRS-80 Model I had a game who's instructions read:

    For sound effects, place an AM radio next to your monitor

    It was a car racing game... the sound effects made a kind of sense... except they didnt stop when you crashed the car :)

    • Yeah, I remember that. There were a number of games for the TRS-80 that used a radio for sound. One of my favorites was a space invaders clone. This was back in, oh about '77 I guess.

      • Heck, the TRS-80 Model 1 was forced off the market because of its radio noisemaking. If I recall correctly, the FCC had let it be sold initially because they didn't think it would be popular but after it sold however many million units they realized that these computer-things would require similar regulation to other common office equipment.

        I had a BASIC program that would play arbitrary music over the radio. It had various subroutines that would calculate something or another and thus generate a specific radio tone. The main program simply read in the musical data and called the appropriate subroutine to make each note.

        Most games and the like however used the cassette-tape output to make sound effects, or even pretty good voices. "Robot Attack!"

        Now where did I put that emulator []?

        • >Heck, the TRS-80 Model 1 was forced off the market because of its
          > radio noisemaking.

          uh, no. It was superceded by a newer model (the III) which was less expensive to build in the configurations people would buy.

          > If I recall correctly, the FCC had let it be sold
          > initially because they didn't think it would be popular but after it
          > sold however many million units they realized that these
          > computer-things would require similar regulation to other commo
          > office equipment.

          it went on the market before the regulation changes, but not by enough to have caused them. It came out, what, Fall of 77? Spring? (hey, give me a break. I'm doing this from remembering my childhoold, not looking it up :). The Atari 800 (late 80? early 81?) was caught in the regulations.


        • Most games and the like however used the cassette-tape output to make sound effects, or even pretty good voices. "Robot Attack!"

          Well, that's a sight better than using the cassette relay for sound. BzzzBZZZZBzzzz...

          "Bandit Got Away!"
  • What I want to know is if you can use this as a means of wireless networking on the AM band. Now it wouldn't do any good for my laptop but I could use it for my two desktops to comunicate with. Anyone know where I can buy a AM reciver wireless network card?
  • There was a game for the Tangerine Microtan 65 (British 6502 system from 1980, started as a single board, expanded by adding cards) which generated sound effects like this, just tune your radio to 750Khz (the clock speed) and listen...

    Of course most people by then had hacked the main board to boost CPU speed to 1.5Mhz!

    Kids today with their surround sound and subwoofers, they don't know they're born...
  • Now, soon, we will not be able to use our laptops in flight. Woo!
  • ... but will someone port this thing to Windows so the less 31337 :P members of /. can have a play with it.

    Not that I don't run linux ... but ... um ... oh just think of the children and port the damn thing ;)

    *cough* xp *cough*

  • and not a damn thing the FCC can do about it,
    since the equipment (the Monitor/Computers) has already be licensed by the FCC. You'd probably need a whole lot of boxes, though. And to make
    sure they were all in phase would not be easy.
  • I heard about an Alaire presentation to a computer group back in the early 70's that consisted enirely of music generated by placing an AM radio next to the Alaire computer. Maybe someone here knows more about that event. I know it has been written about before.

    The more things change, the more they seem to stay the same.
  • by TheLocustNMI ( 159898 ) on Tuesday November 27, 2001 @07:07AM (#2618485) Homepage
    SweetCode [] had you beat on this one! It's a great little site. Imagine, if you will, Freshmeat with all the chaff removed.
  • I can't recall the game, but way back in the days of yore there was a game for the TRS-80 that created sound effects via a radio that you'd set up near the box. Anybody else recall classics like that?
  • Now we can get online and give Dr. Laura some REAL competition!

    Don't forget to listen tonight at 9.....
    Just make sure you're within a 20 foot radius to hear me!

  • ZX-81 (Score:2, Interesting)

    by ThierryD ( 217773 )
    Well, back in 1983, I had a Sinclair ZX-81 (also resold in the US by Timex, I believe) with a whopping 1K or RAM.

    I purchased a program that did exactly that, but wihth the mother board.

    Put a radio next to the ZX and you could hear Jingle Bells. Not great quality, but pretty neat (in those days).

    Almost 20 years later, today's computers still can not beat the power of a ZX-81!
  • Because I'm a cheap bastard I don't have cable tevelsion (cable internet tho). If I turn on my laptop anywhere near the TV, VHF channel 3 gets scrambled. Same thing if a big truck goes by. Another wierd thing is that if I leave my speakers turned on I can hear entire CB conversations broadcast from the speakers -with the computer turned off. I'm pretty sure the speaker thing is the CB transmission inducing through the powerline.
    • Back in '78-'79, I had to turn off my TRS-80 whenever the family wanted to watch channel 12. The computer was in a far corner room, at least 30 feet from the antenna.
    • The CB problem is because those truckers are pushing 100-300 watts or more. I think 4 watts or so is legal for CB, but probably 95% of truckers use a amp of some sort.

      AM will rectify when it gets picked up on your speaker cables, sort of like the old crystal radio, it doesn't take much to create a simple AM radio.

      There are some measures you can take to reduce the interference (even though you shouldn't have to legally, it's them that is breaking the law).

      Try ferrites everywhere, especially on cables that have a grounding sheath. This will choke off current from the ground sheath.

      Keep cord lengths as short as possible. Move the equipment to the other side of the room and see if that helps.

      You can also wrap your whole house in chicken wire. Just make sure the chicken wire has a good RF ground, and also make sure your neighbors don't call any mental health organizations. :)
      • They don't need to be pushing that much power at all.

        I had a CB a few years back, that was just a tiny bit "tweaked". Instead of 4 watts on main and 12 on sideband, it pushed around 6 and 16.

        Once, I was sitting in my truck in front of my parents house, chatting with some CB friends. I came back in, and my parents had heard the whole thing! It turned out that the length of the SPEAKER CABLE was an exact match for the wavelength of one of the channels (or a multiple thereof, not positive which).

        The amp was on, but not playing anything, and somehow it picked up this signal off the speaker wire and spat it back out, amplified slightly, just enough for my folks to hear it.

        A 300W rig (which I never saw, people would get ridiculous power from a simple 30W amp) would let me do that from two klicks away, easy.
      • The CB problem is because those truckers are pushing 100-300 watts or more. I think 4 watts or so is legal for CB, but probably 95% of truckers use a amp of some sort.

        Yup. When I was a teenager, the people down the street were pushing x hundred watts out of a home CB setup. Every time they would key up, the speakers connected to my Amiga 3000 would amplify their voices at annoyingly high volume levels. Scared the hell out of me the first time it happened. A quick conversation with them solved the problem for good. :)
  • Hmmm, works on all systems... watch ... uh..errr hear them keystrokes. A lantern that you can hear as well as see?
  • My girlfriend used to get pretty pissed because when my video card would start doing anything 3D, it would cause a hum on the FM station she used to listen to. I think it was in the 100-105 range. The faster it performed 3D ops, the higher the pitch of the hum.

    I made an openGL app that simply resized a spinnging sphere to random sizes. The smaller it got, the faster it moved, the higher the pitch. I never tried making it play music though.
  • In the US, the FCC allows anyone to broadcast an AM signal under Part 15 [] of the FCC rules, so long as it doesn't exceed something like 47 microvolts at 100 meters from the property line. Unfortunately, most AM receivers need at least 300 microvolts to detect a signal and the signal degrades logrithmically, so unless you have a very large piece of property, AM broadcast will probably be illegal for you.

    Disclaimer: I'm not an RF engineer, but I have worked with several in attempting to obtain an AM broadcast license for our college radio station a few years back. Take it for what you will, and understand that the FCC *probably* won't come after you unless people complain. But, if people complain, you can expect them to triangulate your position, take your equipment, and fine you heavily.

  • Well, the software only works on Linux, which I assume means that Windows isn't suceptable to tempest eavesdropping at all.
  • Here's [] what I'll listen to first when I get this working.
  • This reminds me of a program I had for my Amiga. It would play Greensleeves by moving the seek head in the floppy drive at varying frequencies. There was one for the c64 also, and I'm sure it works on PCs too. Anyone know if such a thing exists for a PC?
  • I've got it on a Ventures disc somewhere...Besame Mucho perhaps?
  • A long time ago I had written a 6502 assembler program on my Apple II that tried to seek track -1 on the floppy drive, then paused a set amount of milliseconds, then did it again.
    I got it so I could play songs by the vibration of the drive from the read head banging into the end of it's arm.

    This did, however, void my warantee.

To communicate is the beginning of understanding. -- AT&T