Disperse This!

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.

<img src=“http://www.remcom.com/storage/example_images/038-03.gif” width=“180” height=“333” alt=> <img src=“http://www.remcom.com/storage/example_images/038-02.gif” width=“180” height=“333” alt=> <img src=“http://www.remcom.com/storage/example_images/038-01.gif” width=“180” height=“333” alt=>
(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.


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.

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.

Gravedigging by the weblackey?

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.


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.

It is simply antenna orientation. Rather surprising that the remote does not work best in the normal/usual position, that is, pointed at the vehicle. However considering the antenna is contained on the circuit board it has limited vertical orientation and therefore probably has limited lobes in the direction we would want it to. Antennas normally have diagrams showing the various lobes (see google for antenna diagram) and holding the antenna straight up like the statue of liberty would work just as well as your chin. The higher frequencies of these remotes would either pass right through the human body and at high power and/or be attenuated at low power.

“your transmitter doesn’t transmit light rays. It transmits a radio waves.”

That depends on the make & model of the car in some cases.

Some years ago, Mercedes was using a light-based keyless entry/locking system for their S-series sedans. Because radio waves can be captured and mimicked in order to steal a car, they used a non-radio-based system on their most expensive models. Whether or not they still do this, I do not know.

I tried something similar, the suggestion was to put the key up to my bottom of my chin and it work. After a while I experimented and the primary factor was not where I held the key but rather how high. Holding they key higher seemed to help. Note - I really didn’t play with the orientation of the key, I will have to try that and see if it is a factor.

I have to agree with Rain. …about rain not knowing much about physics. crap. im sorry. whata horribly rude way to return to these discussions. it was just too easy. and I did play peacemaker before I left… please forgive me. :slight_smile:


Ouch, that hurts, but really, I know I don’t know much about this stuff. But where did I go wrong with my idea? If you can help me understand this stuff, I will be happy to have you insult as much as you like.


When I was getting my ham license I learned that transmitting a radio signal was not as straightforward as you might think. Radio waves tend to spread out from the radiator in multiple directions (in radio a radiator is the thing the signal is emitted from not what cools an engine)

So it seems to me that pointing the transmitter in a different direction than you would expect could very easily result in “better range” It’s probably not the range that has improved but the amount of signal being sent in a direction that will actually reach the receiver, which by the way may not be where you think it is.

The signal may indeed be bouncing and hitting the receiver better than if you pointed it straight at the keyhole. The keyhole is probably not where the receiver is.

There are 2 different issues dealt with here. One is the Auto-start remote, which most of the time, is an RF signal using the 300-450 MHz range, and second is the remote control issue, which most of the time, is an IR signal (light). I’ll address them in that order.

The reason an RF signal could be perceived of getting a larger range could be, as previously stated, because of how the antenna is changed direction. Another reason is that the shape of a human skull is similar to a parabolic antenna, which means putting a signal underneath it, could possibly amplify the signal in 360 degrees. So by sticking the Auto-Start (or unlocking) remote under your chin, or in your mouth, would send the RF signal up through the top of your skull, amplifying the signal. If a person has any technical experience at all, you could find your receiving unit in your car, and by googling the chip on it, you could find a different transmitter that could boost your range up to a mile for about $20. You just have to make sure the frequency is the same, and make sure you can set the address on the transmitter to match the receiver.

The issue with TV remote controls is different because most of the time it uses an IR LED to communicate with a receiver. You can test this by pointing your remote at a digital camera view finder and pressing a button on the remote. You’ll see the end of the remote light up (I used this method to test TV remotes when I worked on TV repairs). Shining this light onto a larger surface (the wall, chin, forehead, etc) would reflect the IR signal off of that surface, and possibly be able to be picked up easier from the receiving end; however as the distance increases between sender and receiver the light would dissipate sooner by doing this, and wouldn’t work as well. This also requires a straight line-of-sight for IR to work properly.


I’m no scientist, but since you asked for help understanding, I’d be happy to explain what I know about light rays and radio waves.

The main thing I know is that light rays and radio waves, being on different parts of the electromagnetic spectrum, are quite different in the following ways:

-You can’t see radio waves. Light waves, on the other hand, are in the “visible” part of the electromagnetic spectrum.
-Light rays don’t pass through solid opaque objects, but radio waves frequently do.

BTW modern remotes for cable boxes DO use RF, often at ISM 2.4 GHz nowadays (plus an old IR diode for TV power on/off).

And they do have directionality and bounding issues. They often use very cheap PCB traces on eg single-layer paper phenolic PCBs. I have seen chip antennae though. Not better, though smaller.

What’s funny is that folks raised on IR remotes continue to point them.