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#1328: Dispersion via Dave's Chin

Jul 13, 2013
This week on Car Talk, Dave has discovered an electrical anomaly: his Audi's keyless remote works better when he points it at his chin rather than his car. Fortunately, he's come to the right place…for a completely bogus explanation. Elsewhere, Brett's Camry is giving him enough electrical shocks to turn him into a walking Van de Graaff Generator; Spencer learned why you should never touch your lug nuts in public on a hot day; and Beth's Accord is exhibiting all the symptoms of a bad clutch, with just one problem: it's an automatic. Also, in a follow-up to last week's show, we hear from Tracy, whose girlfriend's parents offered to buy them a car if they got married. Did he get the girl, and the Lexus to boot? All this, and lots more, this week on Car Talk.

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Tom and Ray share one of their favorite jokes of all time: the bridge to Hawaii.

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7 Comments

Remote Bouncing of the Wall

Aiming the remote at the opposite wall works for TVs and other devices. A good example is overhead projectors: one can never aim at the correct angle of the sensor directly so aim, instead, at the screen and this will disperse the infrared beam so the the sensor gets it.
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Another Dave idea

I believe Dave's head has become a wave guide, which focuses the signal rather than disperses it. But the focus effect goes both forward and backwards. You can do the same thing with a pringle's can. But all these ideas are easily tested. If Ray is correct, and the signal is better "dispersed", then sticking the remote in the ear will work equally as well as the chin. If I am right, then if you stick it in the ear, it won't work, but sticking it on the chin, OR on the back of the head will work. If the "parabolic back of head" theory is correct, then it will only work if you stick it on your chin, and not from any other angle. Who is going to test this?
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Signing off
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MIT needs to get their diplomas back

I'm with Ray on the Dave's chin. That answer about the key was a bogus as bogus gets. The chin is a red-herring. The chin is just a reference, but it, itself, is not value-added. While there might be some benefit from touching the key doggle to the chin, (vis a vis the reflectection that comes off the body), I think the more likely benefit is simply the act of touching the chin ensures the the key is held upright. It is pretty much standard practice for users to point he key directly at the car, like a TV remote, when trying to unlock it. This, however, is the worst orientation for optimal transmisssion. Where as the TV remote works like a infrared flashlight, the car remote is a radio transmitter. This means the antenna of the transmitter should be parallel to the antenna of the receiver. And, while the antenna in the car could be installed horizontally, a vertical orientation would be most reliable. And so a touching the key to the chin makes the antennas allign properly.
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Mental midget.
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Metallic fillings

Have you considered that Dave may have fillings and that they are acting as a transmitter multiplier? I had a car alarm installed many years ago, and the installer told me that when out of range to put it next to my jaw, adjacent to the tooth with the filling. Worked like a charm every time.
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Daves chin

Dave's skull is a close enough approximation to a parabolic radar dish, and that is why his range is doubled when he holds the remote key less entry to his chin.
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mental midget
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Calling from a Payphone!

Wow. I've never before heard anyone on Car Talk call from a payphone. Was this recorded in 2013 or in the '90s? And why did Beth have to pay for Click & Clack's toll-free number? (I guess it wasn't toll-free.) The original Western Electric handset microphones tended to have a bassier frequency response, as evident in the sound of her voice. Being a phone phreak, this brings back memories. So payphones still emit those ACTS coin tones? I guess that means you can still red-box 'em. At least in Schenectady, NY. Glad to hear those humble devices hanging on in the digital age.
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Dave is RIGHT!

It has to do with aperatures. If you aim directly at the receiver, the amount of energy seen by the receiver is a tiny angle. If the aperature is 1cm anf you are 5 meters away it's 4 x 10-6 x the power of the original signal! (sin^2 1/500). But if you bounce it off the wall behind you, 100% of the energy reaches the wall, perhaps 1% is reflected, and the reflections are essentially random. But the receiver's aperature is essentially the whole surface on which the signal is projected. Thus the total energy arriving at the sensor can be greater. Dave's chin works as the wall, the disburder!
Favorite Moment: 
Signing off with both of you bozos cracking up!
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