Dave's Keyless Remote

The Show
41

My 1995.5 Audi S6 (similar to the A6 through much of the 90s, ending mostly in 95/96) has an INFRARED receiver between the pillars of the front and rear doors of each side of the car.

The key fob has an infrared LED on it that points the same direction as the key (protruding from the keyring).

Since I’ve taken the fob apart to clean it several times since I’ve owned the vehicle, and being an Electrical Engineering Tech., I can assure you that in this model of keyless entry there is NO evidence of any RF (radio frequency) transmitter in the device – it is INFRARED only — VERY similar to most television remotes.

I have seen 1996 and up Audi key remotes that are completely devoid of the infrared transmitter, and there are also similar audi models that look identical to mine (might be later 1995 cars, even) that to NOT have the infrared bubble receiver between the pillars of the doors (near the windows - right between them) — which means those cars are RF-only (not infrared).

Steps:

  1. Dave needs to look at his key fob - is there an LED that points the same direction as the key metal? (in a dark room, if i hit the button, i can see a VERY faint dark red blip… your mileage may vary)

  2. Dave needs to look at the side of his audi, between the front and rear doors, at the level where the window glass meets the metal of the door — midway up the doors in the pillar. If there’s a plastic “bubble” there, he’s got infrared keyless entry, like me. IF not, he’s got RF, like the majority of vehicles with keyless entry on the road today.

if it’s infrared:
You guys were correct on the bounce theory, which made me spit coffee i was laughing so much! but, it’s correct! bounce that beam!

if it’s rf:
Dave, do you have any elaborate dental work you’re not sharing with the brothers? Most people can afford to be a little intimate with these wonderful hosts! :slight_smile:

-jre

42

I have worked in car audio for over 6 years and have recently ventured into the realm of home video/audio. I have dealt with both remote issues extensively.
The two remote issues are unrelated due to the type of signals used by the remotes. The TV remote uses a IR (infrared) signal. With some IR remotes pointing directly at the sensor can overload it. The infrared light beam is too bright and blinds the sensor. So when it’s pointed at the wall, the reflected signal is attenuated, actually allowing the sensor to read properly.
The keyless entry car remote uses an RF (radio frequency)signal. Pointing this remote at the bottom of your chin actually uses your skull to focus and direct the RF signal. When pointing the remote at the car or anywhere in the air the RF signal is more widely disbursed. I learned about this from a DEI product trainer. DEI is a large remote start and keyless entry maker.

43

Nobody has mentioned the possibility that by aiming the remote at various objects/directions, the signal strength reaching the receiver in the car is weaker, thereby improving reception.

The reason why that might work is multipath distortion. Multipath is a phenomenon where a signal arrives at the receiver by many different paths. One is the direct line of sight. Another is bouncing off the ground. Another is bouncing off other objects, hills, buildings, cars, what have you.

All of those paths are different lengths. The direct line is the shortest, of course. The longer the path, the later the signal arrives at the receiver.

So what the receiver hears is, in effect, many different versions of the original signal, delayed by varying amounts. All those signals add together to distort the original signal. The effect is like talking in a very echo-ey room. You hear so many echos that it is very hard to understand the speaker. (In actuality yhere are lots of cognitive/peceptual things going on there too, I know.)

But when the original signal is weakened somehow, the multipath signals are also weakened, sometimes enough that the receiver can distinguish the original from the multipath. The effect is similar to whispering in the echo-ey room. It is actually easier to understand than shouting.

I get a similar effect with my in-house FM transmitter that I use to listen to Internet audio streams (like CarTalk) around the house. Mine is very powerful, the maximum allowed without an FCC permit. At maximum signal strength, I get very distorted reception, even on my very good radios. When I turn down the signal, reception improves. (One might object that the problem is really receiver overload, and I do have that problem, but only at at one radio and not the others.)

So I believe by aiming the keyfob in various directions, putting it in your mouth, you are weakening the signal, reducing multipath distortion and thereby improving reception and range.

Incidentally, the transmitter is almost certainly omnidirectional, or has a very slight directionality forwards (and equally backwards.) In order to make a directional signal, you need an antenna that is large compared to the wavelength of the signal, and those tiny keyfobs are just too small. And to make a transmission pattern that is directional both front and back requires fewer elements than one that is directional only to the front. I bet the keyfob is directional, if at all, then equally to the front and back.

44

Dear Tom & Ray,
I love you both as if you were my own.
I am a Transfer Station Operator in the small & confussed town of Shelburne Falls. That would be that I am probably refered to more often as The Dump Lady or maybe The Trash Nazi. While listening to your illustriousnesses concerning the question of the remote control,I likened the occurence to a flashlight pointing into a mirror,don’t ask me why. I think, probably, seeing as I’m a highschool dropout and you are not, that visualizing it in this way seems the only answer. By thr way I kind of ignored spelling class. Love Love Love you both.
Lynne “The Trash Nazi”

45

This is an interesting topic, and I’m not surprised that there’s a lot of confusion around it. Even for the knowledgable folks there are a number of effects that could come into play, and without some specific testing I don’t think it’s possible to state conclusively why this happens.

FWIW, I’m an engineer and have been working on wireless communication systems for nearly twenty years. This just means that I have an opinion. :wink:

Some thoughts (some of which have been mentioned already, but I’ll add a teeny bit):

  1. It’s almost impossible to build an antenna that is truly omnidirectional. I suspect that the majority of the effect that increases range by pointing the fob at one’s chin is just that it tilts the antenna up so that a stronger portion of the field is reaching the receiver in the car. This would be pretty easy to test just by tilting it up perhaps at arm’s length, away from one’s chin, and seeing if the effect is duplicated (I suspect it will be to a pretty good degree).

  2. Human tissue is, in general, not very reflective and mostly absorptive. In other words, the likelihood that one’s head, or any portion of the body, is helping to “improve” the radiation in a particular direction is not very likely. Even if you have a lot of metal dental work or a plate in your head (or an alien implant), the likelihood that it would be positioned exactly correctly so as to increase the radiation in the direction of the receiving antenna is, well, pretty doggone low.

  3. Multipath reflections generally won’t hurt at the very low symbol rates used by these devices, in fact, they usually help. So the absorptive effect of the body to reduce multipath reflection (while not a bad thought, I’ll admit), is still unlikely to help reception and more likely to hurt it. In other words, multipath effects are not likely in play here.

  4. The idea of line-of-sight to the receiver might be an issue if, for example, raising the fob to the chin provides a better propagation path through a car window if it was previously blocked by the door or something. I’d be a little surprised if this were the majority of the effect, but it can’t be ruled out without testing.

I’ve been using remote RF fobs to lock and unlock my vehicles for over twelve years and usually overcome range issues just by tilting or elevating the fob, but more usually by replacing the battery with a fresh one.

A little time with a loop antenna, a spectrum analyzer and an example fob would probably be a lot more revealing than the body simulations linked previously. Somebody, somewhere, may already have done all this, but I’ve not heard of it.

46

This is an interesting dialog. I have a fast oscilloscope in my garage, right next to my Volvo, so I decided to do some tests. I used a simple single loop antenna coupled to the oscilloscope, which I terminated in 50 ohms. I could easily observe the signal from the remote when I was within a few feet. The first experiment confirmed the effect of increasing the signal by holding the remote to one’s chin. (Much to my surprise…) However, nothing is simple. There appears to be a near field radiation pattern (within a 350 MHz RF wavelength, or about 0.5 meters) which has a very distinct remote orientation dependence. That is, the orientation of the remote relative to the plane of the receiver loop antenna modulates the signal amplitude by almost a factor of 10. The emission is not isotropic when you are close to the receiver antenna. In the far field (great than about 1 wavelength), the signal is much less sensitive to remote orientation. In addition how you hold the remote is also critical. Moving your fingers a half inch or so to the center of the remote can increase the signal by about 3 fold. The body does appear to act as an antenna. (I don’t think it is a reflection since a reflection from the body will probably not have enough amplitude to cause this much change in signal. I think it is a change in coupling to the body, and the body is acting as an additional antenna.) Touching the remote to the chin is probably changing the coupling to the body, in a similar way as changing your grip, causing the increase in signal. Changing remote orientation or changing your grip causes a comparable effect; there appears to be nothing special about the chin.

The properties of this phenomenon appear to be determined in part by the remote/receiver distance, with definite orientation dependence up close, and position of the remote relative to the body is important, particular at larger distances.

The previous TV remote explanations are also, I believe, correct. This is a different phenomenon and is based on diffuse reflection. Every modern TV remote I have seen is infrared-based. You may be able to see the flashing IR light if you look at the remote using a Video Camera; best one to use is a security camera sensitive in the infrared. The TV remote LED has a directional emission pattern determined by the lens which is molded into the cap of the diode. The diode is powerful enough to bounce off a wall and still supply a detectable signal to the receiver. (This is easily demonstrated…) The signal reflected from the wall has a high amount of scattered light which is pretty much omnidirectional. This is what triggers the detector on the TV.

Great show Tom and Ray!

47

Very cool experiment and thanks for posting that.

I’ll suggest that far field tests won’t be meaningful if you’re inside a room due to rich multipath reflections. If you take the loop and the remote(and the scope) outside, you might be able to reduce the multipath reflections enough that the antenna orientation effects might be more discernible. I suspect that you’ll still see that the antenna orientation makes a big difference.

The results with finger placement are interesting. Since bodies are mostly water I’m guessing that there could be some antenna modification effects going on due to that. Testing the remote in close proximity to a water balloon might be fun.

48

I think this stunning new explanation could help us search for extra terrestrial life. Imagine the power of our radio telescopes if we had people climb on top of them and aim the output through their chins. We might finally find signs of intelligent life!!! At least on other planets.

49

For all you antenna experts (geeks), I have an application question for this problem. My husband and I are not able to use our cable remote when the dogs are in front of the cable box. We tried bouncing the signal off the (wooden) ceiling and also my husband’s chin but this didn’t work. Any suggestions (which do not involve shooting the dogs)?

50

I heard that it is the metal in fillings in your mouth that transmit the signal from the remote.We are going to try it at the next elementary school/junior high science fair!
It works in my mouth…not in my children’s who have no fillings!

51

I heard about this phenomenon from my brother a few years ago. I told him it was impossible and he was a victim of just one more internet myth (I had just convinced him to stop poring cola over everything in the house claiming it was “the world’s best cleaner”)

But, he was so sure of this phenomenon that he made me come outside to see his proof:

We slowly walked away from our Taurus, locking and unlocking it with the remote until we reached a distance where it no longer worked.

At this point, he gave me the remote and instructed me to point it below my chin and push the button… Nothing happened. I slapped him in the back of his head and heard that familiar hollow knock.

Insisting it worked, he grabbed the keys and tried to demonstrate with his own head, and what do you know… It worked!

Multiple tests showed that he was indeed correct.

I was left with the question, “Why his head, and not mine…?”

I think the only plausible answer is that his skull happens to be a perfect echo chamber. Of course, only skulls without any “interfering material” are able to effectively increase the range of a car remote.

I guess that means that I am destined to a lifetime of having to remember (within about 100 feet) where my car is parked.

Fortunately, all those drivers, like my brother, without the necessary equipment to remember, will always have a remote amplifier to help them locate their lost car.

I guess I’m not complaining.

52

chs727:

Somne questions:

  1. what make a model of cable box ? ( not all cable boxes use IR these days, for example Direct TV provides a High Def box which uses both IR and RF transmissions).

  2. What color are the walls and ceilings. (for IR to “bounce” light colored walls work best. Recall that dark colors absorb light and light colors reflect.

  3. Where is the Television located ? In a corner? By a window or where ambiant light is falling across the unit? (Sunlight and fluorescents can ‘blind’ IR recievers).

  4. Is the Televison really a plasma screen? Plasma is renowned for generating massive amounts of EMI EMF which can blind IR and in some cases local RF transievers ( such as cable boxes and Wifi Access Poins).

53

actually in re-reading your quesiton I realized that my first attempt was an overkill.

There are a number of manufactures who make IR ‘extenders’ and blasters. these can help by placing an IR reciever higher -(usually this is help when one has units stowed in an AV cabinet with doors. Try http://www.xantech.com/. The make a whole host of IR products which could help you .

54

Hey Guys,

Your show is great. I mostly work on my motorcycle ('83 Honda Nighthawk 650) which is nearly as old as I am. I drive between Montreal and Ann Arbor every month, so it’s health is somewhat precarious. Even though you discuss cars, and I deal with my bike, I love listening to your tips. Every time I’m working on my bike, and have just screwed up completely, I remember the (right) way you’ve already described.

Today, for once, I think I can offer an explanation for your keyless remote entry debate: the antenna in the remote doesn’t face in the same direction that the remote ‘looks’ like it’s supposed to be pointed in. While ideally the radio antennas inside the remote is omni-directional (equally strong in all directions), the signal strength is probably not uniform in all directions. Your caller suggested pointing it at his chin to get an improved range, and that is probably just the direction in which signal is strongest.

Now the issue of TV remote controls is a bit more straightforward. There are infrared LED’s in the edge of the remote. They are also highly directional. When you bounce the signal off of your living room wall (or forehead), then the signal gets dispersed very uniformly in the other direction. So the analogy of the signal ‘flying past the receiver’ wasn’t so far off… the light isn’t intense enough to make 2 bounces (off the wall behind the TV, back to the wall behind you, then to the receiver), but it is strong enough to make a single bounce (off the wall behind you and to the receiver).

I hope you enjoy success in your couch-lounging, and opening your car doors from at least 10 feet away. :slight_smile:

Francis

55

I suspect that the reason that holding the keyless remote up to your chin has more to do with antenna polarization than with the reflection of the signal. A vertical antenna sends and receives signals better from another vertical antenna than one which is horizontal.

56

I was told that the metal fillings in your mouth helped “magify” or strengthen the signal.

57

The arcane discussion surprised me. What fantastic
speculation last weekend! Resonant oral cavities indeed!

Those little RF transmitters with the remote buttons have loop antennas that run around the edge of the circuit board to maximize the loop’s area. Such antennas radiate most strongly at right angles to their plane. Most people assume that the signal comes out the end, as it does in infra-red TV remotes. Wrong!

When you “point” the thingy at your chin, you have half a chance to point the beam at the car. If you know what you’re doing, you’ll point the beam at the car whenever range matters.

To sum up: active key fobs radiate most strongly in the directions of their faces, and only weakly from their edges and ends.

Someone here mentioned credentials. I’m an electrical engineer and I’ve designed something kike that.

58

Suggestion? Sure! Move the box. The top of the set should be fine.

59

If the chin is the key, then would not Jay Leno be the PRE-EMINENT expert?

love you guys!

IB

60

moving the cable box to teeter ontop of a monitor seesm so troublesome. Not to mention that the TV may be a flat panel with no room for a box, or the reach of an excited dog’s tail.