larry@kitty.UUCP (Larry Lippman) (11/25/87)
In article <3810@bellcore.bellcore.com>, copp@wind.bellcore.com (*David H. Copp) writes: > A friend once contemplated building a machine to jam supermarket > music systems. Many of the markets in our area buy their music > from an FM station--a subcarrier system--and it appeared to be > fairly simple to put a low-power FM transmitter in a briefcase and > capture the receiver. Damn! I wish I had thought of that while I was a carefree EE undergrad. It would have been easier to implement that the following escapade of my college daze... During my junior year, my roommate (also EE) and I came up with a great (!) idea: to jam the audio at a drive-in movie and insert our own "commentary". This project required weeks of, ahem, preparation. First, we scrounged an old Bogen 100 watt PA amplifier of 1950's vintage, and modified it to run using an external DC power supply - which consisted of a WW II surplus dynamotor. Since the dynamotor required 24 volts DC, we made a temporary installation of two 12 volt batteries in the trunk of my car. The dynamotor also went in the trunk, with a remote control switch. The amplifier sat on the rear seat, and was covered with a blanket. Some "preliminary investigation" at the target drive-in indicated that a 70 volt line transformer was mounted in the base of each speaker pedestal, and the one transformer fed two speakers. We decided to back-feed into the system at 70 volts. On the fateful night, my roommate and I along with two carloads of "supporters" invaded the drive-in. We parked in the last row. Under cover of darkness, I removed the cover plate at the base of our speaker pedestal, and attached two 22 AWG magnet wires to the 70 volt feed. There was enough clearance on the cover plate to allow the magnet wires to pass when the plate was put back. Also, the magnet wires allowed for a rapid - and hopefully inconspicuous - breakaway. I don't remember the name of the movie, but it was a low-budget horror film about witches in England. The movie was ripe for a "commentary". With all connections made, I turned on the dynamotor. After the tubes warmed up, I cautiously advanced the master gain control. Voila! Feedback, even though our own speaker was turned off. It worked so well, that we had to close all windows in the car. My roommate and I engaged in a running "commentary" [y'all can use your imagination here :-)]. The people at drive in went wild - blowing their car horns in delight. The management went nuts. After about five minutes, two people ran out of the projection booth with flashlights and started checking cars. Needless to say, it was time to pull the plug. The fellow who came over to my car looked at us with great suspicion, since we and the two adjacent "support" cars were all laughing hysterically. However, no one said anything to us - I think the drive-in management was still in a state of shock that someone could do such a thing... Since many drive-ins today use an inductive loop AM radio approach, perhaps this would be easier to do using an AM transmitter (easy to make using the power op amps available these days). Of course, such a transmitter would be unlawful to use, and I could never condone such a thing for a prank... :-) <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
max@zion.Berkeley.EDU.UUCP (11/26/87)
This does not equal Larry's anecdote but it does give you a true example of the effective deployment of electronic countermeasures by civilians against obnoxious FM radio reception. I have a friend, whom I will call Joe, who a few years ago was a quiet electronics technician of the old school. Although too young to properly qualify as an old fart, he liked to build things with vacuum tubes. Joe is also a cellist, and a member of a large local family. He likes to practice his cello, or play the organ, for relaxation. Anyway, at the time of this anecdote, Joe had moved into an apartment in Oakland, California. He did not play the cello or organ there, out of respect for his neighbors (nowadays he owns a house, and besides, his neighbors like the music). However, in the apartment building were some Very Noisy People. They would play FM stations at all hours, loud. They acknowledged but did not act on requests to moderate the volume. Now hereabouts this sort of behavior is illegal -- the police call it a 647 violation, Disturbing The Peace, so Joe could easily have complained to the police. But his style was much quieter, and subtler, than that. He built an FM jammer, which came in later years to be passed around a lot and dubbed "the family FM jammer." (This was very much in character -- Joe was always building clever gadgets to fill a need. The family is very handy with things like that, making do -- Joe's parents grew up, of course, in the Depression.) It was a beautiful piece of work: built on a block of wood, with open-air coils, a large glowing VHF tube, and porcelain insulators. It would have been completely at home in a 1930's sci-fi movie with Bela Lugosi in a starched white smock that buttoned up on one side. The jammer used, simply enough, the 60-Hertz power line to frequency-modulate the carrier. With characteristic attention to detail, Joe had made sure that the modulation was just enough to cover the desired channel without spilling over to adjacent ones. Yes, it was assembled and aligned with all the loving care of a commercial transmitter expecting outside inspection. The procedure was simple but delightful. When the Noisy Neighbors decided to play loud FM, and this got to bothering Joe, he would warm up the jammer. Because the jammer needed precise tuning, and also because the problem had now become a sport, Joe worked the tuning dial with the fingers of a safecracker, and all the patience in the world -- I like to think, though I don't really know, that he had a cigar and a glass of port, perhaps Graham's Malvedos 1955. Presently a horrific buzz would replace the (inevitably pounding) dance beat audible through the wall, provoking vaguely audible expletives of discontent. Someone would change the station, and the music would return. It didn't bother Joe; he was patient, and he was sure of his quarry. Eventually he would find the new station and they would change it again. Sooner or later there were expletives of resignation and the receiver was turned off. To his fortune, they rarely played anything but FM (AM, of course, would have been even more manageable, but records would have required a radically different approach). All of this had the effect of translating a nuisance into good clean sport, at least for a patient cellist like Joe. Naturally, as a law-abiding citizen, not to mention a commercial licensiate of the FCC and bound by the statutes of the Communications Act of 1934 as amended, I would have been horrified and obliged to report this behavior had I not learned of it well after the fact.
robert@uop.EDU ( ) (11/27/87)
there is a guy in one of the fraternity houses here that built a "black box" transmitter, it had an on switch and a VCO, he would tune the little bugger around the FM band and run to full quieting his neighbor's stereo.. this was great, since it did not hurt the stereo at all! and it was a pocket sized gadget.. the other thing to note, is a CB that runs a little high on the out- put side (that is your buisness not mine) will often times put out enough RF to modulate a speaker. we had a band amp go nuts with a guy about a block away from our rehearsal area, everyone standing around discussing the next gig, when "Yeah Goldduster, thats a 10-4" comes blasting out of one of our amps.. i guess he just was putting out enough to excite the plate in the tube section, and it amplified the differences it had.. also i noticed when i was a kid (you were a kid?) that when i tuned my radio shack aircraft reciever (the one that you put together with spring clips) that it is so unsheilded that it will put nice black and white bars across your T.V. screen! just tune it around until it happens and then label the dial for "channel 10" or whatever, this was great, as it took my sister a couple of days to figure out how it was that whenever she wanted to watch something, the reception went crazy! oh well...
wtm@neoucom.UUCP (Bill Mayhew) (11/29/87)
<< Larry's Drive-in confession >> I can't come close to being as inventive as Larry and the truly monumental drive-in prank, but it did remind me of being a devious prankster in highshcool and college. My favorite prank was rigging lockers in highschool. My friends and I would cruise the streets on trash pick-up day looking for old TVs and radios. We'd grab the speakers to make oscillators for lockers. One time I wrapped up the 8 D-cells for the oscillaotr in brown shopping bag paper. When the janitor found it (naturally the guilty return to the scene of the crime to gloat over their exploits) he saw the blown tubualr battery packs and thought it was a bomb. I don't know how he and the principal missed me, as I was sitting on the steps about 20 feet away colapsed in laughter. The best locker device was an old truck horn that a friend picked up at a garage sale. About a dozen kids got together and descended in several waves on all the local Radio Shack stores to get 96 D-cells with our free battery-of-the-month cards. The trigger device was a little 12 volt crystal-can relay held open by an almost dead Radio Shack 9 volt battery. When the battery went dead, we planned, the contacts of the relay would be sacrificially welded together and activate the horn at deafening volume. We warned the planter not to test the trigger, as it was planned to be sacrificial. We became suspicious, when after 1/2 hour there was no blaring horn audible. The planter admitted to having tested the trigger. We conned the planter to go out and kick the locker in hopes that it would jar the horn to life, as resitution for violating our orders. When he kicked the locker, the relay crippled by tre previous test, set the horn off sounding like a half dead cow. Somehow, we got away with it, eventhough it should have been obvious to the teachers that we were guilty. I think that the teachers were secretly amused too. I got my "bomb" oscillator back by stealing it back from the physics teacher's classroom, where it had been sent by the principal for "analysis". I was much less inventive in college. Actually I had some grandiose plans, but never got the time between studying to implement them. The best prank there was a time delay device built with a 555 timer and a couple of 7493 and a 7400. I set it up so that after 1/2 hour, the last 7493 wold set a latch and energize a reed realy to turn on a motor run by a D cell. The motor as directly attacted to a thread spool on the motor shaft. The motor supplied just enough torque to overcome the friction supplied by a paperclip and allow gravity to take over and unwind several feet of thread from the spool. A giant squishy plastic tarantula purchased at a Spencer Gifts was attached to the thread. The whole contraption was concealed in a small box that had originally been the shipping carton for a Triad interstage audio transformer. The device was small enough to sit on top of a pull-down movie screen in the front of the Electromagnetic Fields Theory I class room. One day, about half way through a particularly uninteresting lecture, the spider made its descent. What was fun was that the prank device was clearly visible to the class before the descent, but not the instructor. Fortunately, the general laughter that erupted saved the truly guilty party (me) from being nabbed. Bill Mayhew NEOUCOM (wtm@neoucom.UUCP)
robert@uop.edu (Hi how ya doin) (12/24/87)
In article <313@sas.UUCP>, jcz@sas.UUCP (John Carl Zeigler) writes: > Then there is all those things you can doo with nitric acid. . . Oh, you mean the "Lightbulb joke" ?? > Pyromania ? me???? no way!!! me either!!