Dave's Keyless Remote


#1

On this week’s Car Talk, our last call really took the biscotti. Dave, from New Jersey, thought his teenaged son was playing games with him when his son told Dave the range on Dave?s Audi keyless remote would be much improved if he pointed it at his chin, instead of the car. Much to Dave’s amazement, his kid was right! But… can this really be?



Ray thought so, and developed a nice, little “Dispersion Theory” of radio waves. (Where would we be, without Male Answer Syndrome?)



Tommy’s response? “Disperse THIS!”



What do you think? Share your thoughts (they can’t be any more wacko than ours) right here. And if you’ve got a friend who may know something, Dave’s our Call of the Week – so go ahead and download him, and spread the Gospel of Dispersion.



Thanks,



Tom and Ray

Click and Clack, the Tappet Brothers



P.S. Since Dave called us, we were alerted to this interesting study. Who knew? Certainly not us!


#2

I’m a theologian. I suggest applying Ockham’s Razor to this questione disputatae. The simplest possible answer is that the remote’s transmitting antenna is located in the end that points away from Dave’s chin when he holds the remote up to his mouth.


#3

I used to support Genie garage door openers and noticed a similar happening. If you hold a remote too close to the powerhead(thing on the ceiling) when you’re programming the remote, the signal cannot be picked up. You need to move it back a few feet in order for the receiver to pick up the signal. So, I’m going to have to agree with Tommy’s theory about signal dispersion. The signal needs to have room to spread out to the point where it will consistently be picked up by the receiver.


#4

I say chins and oral cavities and far walls are red herrings! Bouncing signals and dispersal are boooooogus! The answer is much simpler. The directional antenna in the transmitter was installed in reverse orientation. The strongest point of origin for the signal is at the wrong end of the remote so when you point it at anything opposite the receiver, you are really getting the strongest signal to the target. I agree that the transmitter generally has more power than the minimum needed for operation, so it can work even when assembled incorrectly, just not as well.


#5

And by Tommy, I actually meant that Ray came up with the brilliant and well thought out theory about the dispersion of the radio waves.

Another trick to get longer range with remotes is to clear out the receiver and reprogram them(sometimes it works, sometimes not so much.) The car itself produces interference that can drastically cut down on the range of a remote which is unavoidable with a car remote.


#6

WHICH ONE IS CLICK AND WHICH IS CLACK???
BUT Ray – was it Ray? – was right, but for the wrong reason. Kinda.
Most remotes are infrared. Bouncing the beam won’t (necessarily) give it farther range, but it will WIDEN THE BEAM, therefore making the target easier to hit. Walls, mirrors, faces, your sister’s backside, even the '92 Tempo out in the driveway, can all work, provided they are not four blocks away.
Tommy? sit down. sitting? good.
You Lose.
(sorry)
seeya,
the ratmobl


#7

Keyless remotes are high frequency radio transmitters, not infrared. The phenomenon involves how the human body is used as a re-radiating antenna by coupling it to the fob by holding it at the chin. A company called Remcom has investigated this phenomenon and even sent a letter to Car Talk with the results. You can see the details of their investigation at their website at:

http://www.remcom.com/varipose/varipose-examples/keyless-entry.html

If you don’t want to look at all the details, here’s the letter sent to Car Talk, copied from Remcom’s web page:

Remcom develops software to analyze antennas including their interaction with human bodies. Looking for a challenging example, and being devotees of your show, we used our software to investigate the Keyless Entry phenomenon described in your classic clip Never Underestimate the Power of the Chin. We found that holding the key to the chin greatly increased the currents flowing in the hand and chest regions compared with other positions, these currents then radiating a signal roughly four times as powerful as with the key in other positions. You can view some false color renderings of these currents with the key held in different positions at our web site at www.remcom.com,


#8

I don’t think I’ve seen an infrared remote control (except for my cheap walmart TV) in a long time.

The whole theory about pointing the remote at you chin has been around forever, but it does seem to improve the range somewhat. I’m not sure why. Try it next time you are walking across a huge parking lot to your car. It does look silly though.


#9

First, TV remotes almost all use Infra Red transmitters and receivers, whereas car remotes almost all use some form of radio transmitter and receivers. The IR transmitter in the TV remote transmitter works similarly to a broad beamed flashlight. The receiver on the TV can be thought of looking at the room with a limited field of view. If you’re slumped on the couch, it is possible that pointing the remote directly at the TV will still be out of the view of the TV receiver. If, however, you bounce the beam off the wall or other object (not too far away), the receiver will then be able to see the signal. This is essentially geometric optics type stuff, what you’re used to with vision and light.

Radio on the other hand is a little different. Maybe the key difference is size - the radio waves are much larger than light waves. The antennas needed to direct radio waves as beams are much larger and unpractical to fit in your pocket. Therefore the little keyless remote you have for your car sends out its radio signal in a pretty much omni-directional pattern. Antennas and radio wave propagation in the presence of various metal and dielectric objects that are of the same size or larger than the radio waves is non-trivial, but suffice it to say that there are certain size antennas that work best (maximum range) with the specific radio wave size your keyless remote emits. Sticking the transmitter up to your chin effectively increases the size of the transmitting antenna to a more effective size and therefore increases the range. Freaky, using your head as part of the antenna, but it works.


#10

Correct. This is what I was saying in my entry above. Check out Remcom’s web site for information


#11

It’s quite simple really. The key fob is an omnidirectional transmitter. Holding it to your chin places it at the focus of the parabolic reflector that is the back of your skull. You are facing the car when you press the button, and the back of your skull reflects and concentrates the radio waves toward your car. Presto.


#12

Mine worked from 30’ while on the ground and 100’ from the second floor office window.


#13

Thought either Click or Clack had a physics degree from MIT. I’ve thought about the car remote but was too embarassed to call in. I have found that pointing the remote at your head increases the range by about 50%. I usually attract a crowd when testing this, so my results are pretty approximate.

First, the car remote is a radio wave transmitter. Pointing the remote away from the auto opens the door. Ergo, the radio waves are emitted in all directions and are not focused in a beam. My theory is that placing the remote near your head bounces some of the waves toward the auto, thus reinforcing the signal and increasing the range. is a different theory than the idea that you are turning your body into an antenna. To test this, I moved out of range, and put the remote inside a stainless steel pot and pointed it at the auto. That worked. Pointing the same contraption away from the auto did not work. For anyone who objects that electronic waves aren’t reflected, I ask them to remember “ghosts” in the days of rabbit ears. No research on infrared television zappers.


#14

Guys (and ladies): It’s fascinating about the keyless remote, especially Remcom’s theories. But many TV remotes still use infared signals. Tom (or Ray): when you lie down to watch the Red Sox replays during the day, you’re probably using your glasses to see the screen. The infared signal is bouncing off your bi-focals, which spreads the red signal and makes it more readable by the infared receiver. Best to all - Geezer2


#15

If the antenna is a simple loop then it is not an omni-directional transmission. Rather, it will have the anisotropic radiation pattern of a dipole. That means there’s more intensity orthogonal to the plane of the loop. Therefore, there will be some angular dependence of the reception length even if there’s no human body present. I’m sure the people at remcom knew this when they did the simulation so if they didn’t mention it in their response, that must mean the body-scattering is a more important effect.


#16

But it also works to some degree pointing it at soft tissue (stomach) and works well at forehead. If so how does the transmission get through your forehead twice? Once on the way in, bounces off parabola of rear of skull, and once on the way out?


#17

no, youre all wrong - the remote is possessed by the same gremiln-demon that lives in my Jeep’s 5-speed peugot transmission, its just waiting to lull you into a false sense of security and then blam- one day you will put the remote to your chin and hit the button and the car will start and chase you down the street with murderous intent like steven king’s “maximum overdrive”. dont say i didnt warn you…


#18

Someone needs to perform a few experiments to see if this happens on other cars as well. Does anyone know how to contact the Mythbusters on the Discovery Channel?


#19

I think I know the answer.

Your head is acting as a parasitic element in an antenna array similar to a Yagi Antenna (you know those funny looking TV antennas on roof tops) only there are two elements; your keyless remote (the driven element) and your head (the parasitic element or reflector). When you hold the remote up to your chin you are coupling RF energy from the remote to your head and since your head is close to a resonant size in relation to the wavelength of the remote (around 300 MHz), you create a larger antenna aperture for the signal to travel further. Your head is approximately resonant at UHF frequencies (200-40MHz) so your head is acting as a parasitic element in a two element antenna! It seems to be directional as well. Turn around and it seems to beam the signal in the other direction.


#20

Wireless remotes of this kind use radio frequencies between 300 and 400 MHz. This means wavelengths between 1.0 and 0.75 meters, respectively. Since the wavelength is so much bigger than the little transmitter key, there is no directional beam or aiming as with a TV remote. (The latter uses infrared light with about 1 micron wavelength–much smaller than the emitter). The only possible explanation I can think of is that if the transmitter is held close to Dave’s head, his head and upper body may act as a reflector, with the reflected waves interfering constructively (in phase) with the direct ones. This would concentrate the RF field in the forward direction.

I am a physicist and RF design consultant.

Jonathan Allen, Ph.D.