Does the remote entry work better when pointed at your chin?


#1
This week on Car Talk, do things work better when they're... pointed at your chin?!

Okay, more specifically: Chris from Farmington, Michigan has a friend who insists that his remote entry will work from farther away, if it's pointed at the user's chin. (You can hear Chris call with Tom and Ray right here.)

And what does Chris think of all this? One word: booooo-gus!

Ray, as you can tell if you listened in, offered a rather impressive series of lame, pseudo-scientific explanations.

So, now, it's your turn. Save our hosts from their own Magliozzi version of Male Answer Syndrome. Anyone out there with a legit background in electrical engineering want to chime in and let us know what you think? We promise to drag Ray over to the screen, to show him your answers.

Yours in the perpetual pursuit of non-bogus answers,

The Lackeys of Car Talk Plaza


#2

I heard this too, and spent a week walking thru the parking lot looking like an idiot with my key fob on my head. One day I realized–all I had done was turn the fob around. The opposite end was pointing at the car. It has NOTHING to do with your head and anything bouncing around in it–but everything to do with the direction you are pointing the remote entry mechanism. I know Nissan and Honda attach theirs to a ring at opposite ends, so for each car, I have to point different ends. I’ve extended the distance at least 4 times to open my car remotely simply by turning the darn thing 180 degrees. So, no more looking like an idiot for me!


#3

I am an amateur radio operator licensed in the “extra” class, so I should know what I am talking about.

Remote Keyless Entry frequencies operate between approximately 315 MHz and 433.92 MHz, but are generally centered at approximately 315 MHz and 433.92 MHz. At these frequencies, operating range is affected more than anything else by altitude above surrounding terrain. Thus to maximize range, hold the transmitter as high as you can. Taken to an extreme, don?t increase your altitude to the point that you significantly increase the distance, such as trying to start your car parked out front while you are still on the 99th floor of a skyscraper!

A typical 1/4 wavelength antenna for these frequencies would be about 20 Cm, roughly 9 inches. Most remote transmitters do not have antennas nearly this large, hence, they are tend to be omnidirectional in function, meaning they work equally poorly in all directions.

The human body actually absorbs radio frequency energy, however, absorption is less of a problem at these frequencies than at shortwave frequencies.
While radio waves do bounce, they tend to bounce off of electrically conductive structures or the Earth (or moon for that matter). A person’s mouth is too small for such a purpose. One could experiment by covering themselves in aluminum foil and holding the transmitter at various lengths probably about 18 inches from the foil, and create some directionality that way, but I doubt it would be enough to notice. Waves will also bounce off surrounding buildings, and experimenting there would attract less attention than wearing the tin foil.
So, to summarize, hope your vehicle is not hidden behind a larger one; maximize your range by holding the transmitter as high as possible; and keep fresh batteries in the transmitter (and keep batteries warm in the wintertime).


#4

Simply put:

The antenna to receive the signal is mounted on the dashboard at a height above the bulk of the body of the car. Raising the key fob to head level, rather than elbow or thigh level will let the radio signal have “line of sight” to the antenna and not be reduced by the car body and surrounding objects.


#5

I tried this today with my Oldsmobile Intrigue, using the lock function since it makes the horn beep. I was about 30 feet from the car. With the remote in front of me and pointing the fob with the flat side parallel to the pavement, there was no response. Then, the fob still in front of me, I pointed it skyward and the horn beeped. I did this three times, same result for each orientation. My guess is that orientation has something to do with it, and there is no “canyon effect” other than coincidence.


#6

Did they not air this one years ago?


#7

For years I was the “go to guy” for keyless entry problems at my GM Dealer. We had both factory installed systems and Dealer installed systems. One of the Dealer installed was the VSS 350 (from Code Alarm) this reciever had a external antenna (just a wire) and easily had 35 yards range. On the GM intalled systems at times you had to be standing next to the car (I replaced many recievers over this).

None of my customers ever asked me about this but the did other equaly stupid things like leave their guns,drugs,money,multi thousand dollar CD collections in the car when they left the car for service.


#8

People with guns that don’t work usually find out that it works all the time when pointed at their chin. Remotes are safer too.


#9

Yes it does! Because I am a RF engineer I wanted to know why. There is a good reason for this effect: remotes work usually at a frequency of 432 MHz that means a wavelength of about 70cm. The remote itself is a very small device, therefore the antenna gain is low. If you point the remote to your chin, or as I do it to the forehead, you couple that low gain antenna to your body, which consists mainly of water and is a pretty good conductor. The result is a higher antenna efficiency.
I tested it in the Lab, I had a test receiver in a distance of about 5 meters, close enough that I could read the display from that distance. The receive level at the test receiver increased by 15dB when I held that remote to my forehead. A level increase of 6dB equals a range doubling. 15 dB is therefore more than range doubling.

It’s simple physics, nothing magic.

Harald


#10

So if it works off a human body what device could a “RF engineer” come up with to really help out with the range? Could you make any money off a "range increaser?

Like I said with some GM’s you had to be standing next to the car so doubling would give you what? another 3 feet.

I want a device that gives me 50 meter range off my remote,do I have to get a bunch of friends and link arms?

Did you test this in a parking lot? on several different cars,in different weather conditions and times of day? with several cars blocking the way? Give me some real world test data.


#11

I am not an engineer, but was told by the person who installed my car alarm and door opener that to increase the range of the device, HOLD IT UPRIGHT AND PRESS IT TO THE UNDERSIDE OF YOUR CHIN.

He was absolutely correct. Doing that increases its range at least by a factor of 3 or 4.


#12

Harold, I don’t buy it. Just because a body conducts electricity does not necessarily make it a better antenna. Anyway, if this is how it works, why not point the garage opener at your car body? That’s a big hunk of steel, a MUCH better conductor than the human body. Makes no difference, as far as I can tell. It’s just raising the transmitter that make a difference.


#13

Most car remote controls operate in bands of
frequencies near 315 mHz and 433 mHz - where
the human body is a pretty efficient
absorber of radio waves - so the signal from
the remote control isn’t going to do much
bouncing around in a human mouth - it’ll be
absorbed.

Radio waves at these frequencies pretty much
travel in straight lines, except when they
hit a reflecting, conductive surface - such
as a metal car body. So I suspect that what
is happening is that when you hold the
remote in your hand, it’s probably at belt
level - when means that there may be other
cars between you and your car and the signal
om the remote is scattered quite a bit and
its strength at your car is lower because of
this.

But when you raise the remote to your head
level, the signal likely has a clearer path
to your car and the signal is stronger.

A test would be to find a spot where the
remote control barely works at head level,
then back off till it doesn’t work at head
level. Then, holding the remote over your
head, jump as high into the air as you can,
pressing the button on your remote control
to see whether it now works - screaming
during the jump is optional.


#14

Hi,
I think if your use a conductive rod (aluminum, brass, copper etc.) of the correct size, e.g. 1/2 wavelength or better 3/2 wavelength of the transmitter frequency it might work even better. The human body has approximately 3/2 wavelength at 432 MHz, but has some ohmic losses. It also needs to be determined at which point along the length would be the best feed point to couple the remote to this antenna. A further increase of antenna gain is a reflective wall e.g. sheet metal. Positioning the antenna in the right distance to the wall (about half wavelength) can also give some additional boost. Finding the right polarization (horizontal or vertical) is also a way to get more range.

By the way I tested it in the antenna lab of our company. (One of our product is satellite antennas, we do complete satellites as well)


#15

The conductive body has to be resonant to be effective (see above)


#16

Oh, in the spirit of the show, I think that screaming is a required part of the test. In fact, you should do it screaming and non-screaming, comparing the results for each!


#17

Several years ago a friend showed me the under-the-chin (neck) method. I think it works great not only for extra distance, but also if your key fob battery is getting weak. Additionally, we have an RF gate opener on our driveway (about 50 yds. away). If I just stand on the patio and point it at the gate I get nothing. But while standing in the same spot, if I touch the end of the remote to my neck and raise my other hand in the air, the gate opens every time. I’m not an engineer, but it seems like maybe my whole body becomes the antenna…


#18

As both an engineer, and a Ham radio operator, perhaps I might add something to the discussion.

While some posts have noted that the body is water, and therefore a reasonably good conductor, it doesn’t explain why the effect vanishes away from your mouth as it does. Indeed, putting the remote about waist high should be the most effective position if that were true.

There is another more viable explanation from antenna theory.

By putting the remote in front of your mouth, you are creating a Yagi type antenna. Briefly, a Yagi antenna will focus radio energy along its axis, thereby increasing the signal in that direction. Starting from back to front, a Yagi antenna consists of a “reflector”, “driver”, and usually several “director” elements. They are made of metal, but insulated from each other. The refector and director elements are passive. Only the driver element generates (or receives) radio energy.

When you put the remote near your mouth, your metal dental work acts as the reflector, the remote as the driver, and the keys as the director elements, creating an ad hoc Yagi antenna. If you don’t have metal in your mouth, eye glasses, earrings, neck jewelry, or even your bare head will work, but probably not as well.

Even a very poor Yagi will double or triple the signal intensity along its direction, thereby explaining the increase in range.

When you open your mouth (assuming you have metal in both jaws), you enhance the “reflector” performance for the wavelengths typically used for car remotes, so opening your mouth could also make a difference.

Sorry Ray, I tried to find some support for the “canyon” effect, but couldn’t find a shred of evidence for it.

Peter Higgins, PE, N6PH (Extra Class Amateur Radio Licensee)


#19

Maybe it’s all that silver in your teeth ?


#20

The caller who posed you his lemma
Of the keyfob in mouth - range dilemma
The answer is found
In the height above ground
Of the keyfob transmitting antenna