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Disperse This!!!

edited July 2013 in The Show
On this week's Car Talk, our last call really took the biscotti! We heard from Dave in New Jersey who called in to share something surprising: if you point your keyless remote towards your chin, the range is greatly improved.

How did he get this information? From his teenaged son! If our kids told us this, we'd look for hidden cameras but Dave decided to try it out on his Audi, and lo and behold, it worked. Now Dave wonders if it's really true.

Ray developed a spontaneous case of Male Answer Syndrome and trotted out a nice, little "Dispersion Theory" of radio waves.

image image image
(Image via www.remcom.com)

Tommy's response? "Disperse THIS!"

Listen to the call, and tell us what you think! Has Ray shattered his already thin credibility? Do you think the science bears him out? Got any wack-o theories of your own to add to the mix? We want to know.

Thanks,

Tom and Ray Magliozzi.

Click and Clack, the Tappet Brothers

P.S. Since we first aired this call, some actual scientist fans took it upon themselves to put Ray's "Dispersion Theory" to the test. You can read their findings right here.

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Comments

  • QED: Fits of Reflection and Transmission

    Start at the 30:00 minute mark until you get tired of the lecture.

    Also at 1:20:30 "Light really doesn’t reflect off of anything"
  • If you take the unit apart you will find the antenna is oriented lengthwise on the PC board. That means maximum radiation is at a right angle to the PC board. Point the remote at the car and it is in the minimum radiation pattern of the transmitter antenna. Point the remote at your chin and the receiver is now in the maximum radiation pattern of the transmitter antenna. The 'chin' had nothing other to do with this but to get you to 'point' the transmitter properly.
    Best, Dan.
  • I recognize this topic has been discussed in the past with input from the scientific community. Having listened to the show today, and having read the research done on it, I have a few comments and questions.

    In looking at the study done by Remcom, my question is about health issues. Remcom determined that indeed pointing the keyless entry unit toward ones face increased the signal strength. Usually, with radio transmitters, safety concerns dictate to lessen the amount of signal exposure to our bodies, when it can be so directed (cell phones, cordless phones, microwave, etc.). Is it possible the reason why the transmitter antenna is orientated toward the vehicle rather than toward our bodies, even if the signal strength to the car may be increased doing so, is a potential health risk? Finally, in regard to car keyless entry units, perhaps a new battery in the unit might give it more distance even when pointed as it was designed.

    Part II: TV remote controls got thrown into this discussion. They use a completely different technology than keyless entry devices for vehicles. The vast majority of remote controls for household electronics use infrared light transmitters and receivers, rather than radio waves. Interestingly, Ray (or was it Tom?) got it correct when he spoke of dispersion of the source. The infrared signal from most remotes is produced by a single LED (Light Emitting Diode) source. LEDs have this habit of being very directional. In light this is referred to as "collimated". It is one of the problems with using LED light sources as general lighting or flashlights, in that the light follows a very restricted (non-dispersed) path, so while they are great at targeted lighting, they leave the rest of the area surrounding them dark. The fix is a diffuser, but diffusers also scatter light and make it less bright as a result. That is why LED lighting for homes and flashlights have many LED light sources over a broad surface to try to spread the light around more. Getting back to remote controls, the manufacturers generally are more concerned with providing maximum distance at minimum power requirement, so the LED is usually not diffused, and indeed if one points the remote accurately toward the receiver in the device (TV, DVD, CD player, etc) it works well. But the problem is when one misses the receiver window, or there is something blocking the direct line between the remote and the receiver. In those situations, if the receiver is sensitive enough, "bouncing" the infrared light source off of a wall, or your forehead, may allow the remote to activate the receiver without a direct "hit", as the light gets bounced around and may reach the receiver at numerous angles. The reason this "bounced light approach" doesn't work well when pointing the remote toward the device is because, there is inadequate surface area facing toward the receiver to diffuse or disperse the light to the receiver, and by the time it gets rebounced from the opposite wall the intensity is too low. (Again Ray(?) (one of these days I'll remember who is who) got it correct).

    So, laugh all you like Tom (or was it Ray ;-)), but Ray (or was it Tom) had it correct when he said the remote got dispersed (diffused) and that's why it worked "better" when bounced off a close object than when incorrectly aimed, as "off the wall" as that might sound...
  • Isn't this a replayed call from 5-10 years ago? Please tell me it is, and that they aren't rehashing this very old topic.
  • On slate.com we call it "click bait."
  • I think it a question of diffusion. I thought of an experiment you can use to test it. In a room that can be made completely dark, place a target on one wall and stand by the opposite wall. Take the headlight off your bike. Turn out the room lights spin around a few times. Now with just one flash of your light, try to hit the target. Most likely you missed. Don't move the bike light. Now place the diffused glass in front of the light. I predict some light will hit the target. Your not so smooth chin diffuses the radio waves as the glass diffuses light. This might be why greenhouses use diffused glass.

    If you don't have a bike light and some diffused glass, you can just use a a rifle and a shotgun. Be careful that you don't point either gun at your chin.

    Just as the shotgun has less range than a rifle, it will, because of its diffusion, hit the target many more times. I think that is called the shotgun effect. Some guys use this approach when looking for romance.

    On the other hand, I struggled with physics in eighth grade, so maybe I have just wasted your time if you have read this far. Sorry.
  • When the energy from the remote radiates out from the transmitter, light rays go in all directions, and very few of them in the direction of the car. However, when you point it at a concave surface (open mouth, chin), the light gets collimated, so that, after reflection, all the rays are traveling in roughly the same direction, making for a much more concentrated signal.
  • @LWHUFF, your transmitter doesn't transmit light rays. It transmits a radio waves.
  • Whitey

    I don't know much about physics, but I think that light, and radio are both just subgroups of electromagnetic waves. So they should behave pretty much the same way.
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