jjoshua@topaz.rutgers.edu (Jon Joshua) (04/09/90)
Heard this from a friend...
Date - 1980. Person is driving a '79 Monte Carlo through town. All
of a sudden the windshield cracks. It was not caused by a kid
throwing rocks because the crack was rather straight. Anyway the
person pulls off the road and a cop pulls up a few seconds later. The
cop had been using radar and the windshield had a built in antenna
wire.
Could radar hitting the wires in the glass cause them to resonate so
much that the glass cracked?
JOn.
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_____________________________OO_____O___hfdhksjdhfksjdfs_______||__________||__starpath@athena.mit.edu (David E Hollingsworth) (04/09/90)
>Heard this from a friend... >Date - 1980. Person is driving a '79 Monte Carlo through town. All >of a sudden the windshield cracks. It was not caused by a kid >throwing rocks because the crack was rather straight. Anyway the >person pulls off the road and a cop pulls up a few seconds later. The >cop had been using radar and the windshield had a built in antenna >wire. >Could radar hitting the wires in the glass cause them to resonate so >much that the glass cracked? Yeah, I had a friend who had that _exact same thing_ (well, almost :->) happen to him. He was driving along, went around a corner, and his windshield cracked... into 4 separate pieces! Apparently some radar gun assembler had put a diode in the wrong place, and changed the normal sinusoidal output into a pseudo-square wave. The spot that my friend drove around was a popular corner for cops to hang out at, so when two different highway patrolmen tried to clock the same guy, both with faulty guns, the waves _just happened_ to be at right angles. Which caused his windshield to split in four distinct parts...each taking a quarter of the original space. When both cops stopped behind the guy, they apologized for the problem, but claimed that they couldn't be held responsible, because his windshield had antenna wire imbedded in it. When he told him that he couldn't believe it, they showed him some pictures of other cars, where the windshield had broken, and even melted due to resonance from the radar waves. Even scarier, cars that use radar detectors and have the radio turned on to certain A.M. stations have been known to crack ALL of the windows in the car. Foretunately, most of us haven't noticed this, because it doesn't happen unless the car happens to be driving over a grooved road, so that the car resonates with the radio waves. --D. Hollingsworth P.S. I just wondered if someone could tell me how to use this process to produce a microwave freezer. ------------------------------------------------------------------------ ---------- |David E. Hollingsworth |"D over mu = kT over q...notice that this is true | |starpath@ATHENA.MIT.EDU |because it rhymes both ways! mu over D = q over kT)"| |96070-2274 <-MR. ZIPPY #9 | -Prof. Fonstad, Semiconductor Devices (I think) | ------------------------------------------------------------------------ ----------
dalyb@godzilla.UUCP (Brian Daly) (04/09/90)
In article <Apr.8.17.57.00.1990.17771@topaz.rutgers.edu>, jjoshua@topaz.rutgers.edu (Jon Joshua) writes: > > Date - 1980. Person is driving a '79 Monte Carlo through town. All > of a sudden the windshield cracks. It was not caused by a kid > throwing rocks because the crack was rather straight. Anyway the > person pulls off the road and a cop pulls up a few seconds later. The > cop had been using radar and the windshield had a built in antenna > wire. > > Could radar hitting the wires in the glass cause them to resonate so > much that the glass cracked? > I doubt that the electromagentic energy emitted by the police radar would have the effect that is mentioned here. First, the power output of a radar gun is relatively low. Following the inverse square law, the amount of energy received at the car would be a fraction of the radiated energy. This would hardly be enough energy to crack a car window (did you ever see how hard it is to crack tempered glass?). Second, since the wavelength of a radar signal is very small, a car antenna (wire) is not an effecient antenna for the microwave radar signal. Thus, not much of the radar signal will be received by the car antenna. -- Brian K. Daly WB7OML @ AG Communication Systems, Phoenix, Arizona UUCP: {...!ames!ncar!noao!asuvax | uunet!zardoz!hrc | att}!gtephx!dalyb Phone: (602) 582-7644 FAX: (602) 582-7111 ~