A car's remote keyless entry fob

[bPer]

From yesterday's commentary:

.... Warren also asks:

Another unexplained phenomenon: Do you know of anyone who can explain why I can hold my car's remote keyless entry fob to my chin and have its range tripled, or even quadrupled? Try it. Yeah, it works. Really!

There's the challenge for this week, folks. A cavity-resonance, antenna effect, or just what? Let us know your theories....!
I have a friend at work who claims this too. I've seen him demonstrate it several times. I have no idea what's going on, so I'd like to hear what people here have to say about it.

I will point out one thing I've observed when my friend has done the fob-to-chin trick. Normally, he (like most people I've observed) points his fob towards the car as he pushes the buttons. When he puts the fob to his chin, though, it is pointed upwards, and possibly rotated from its previous (unsuccessful) orientation. I've read just enough about antenna design to know that some antennas radiate differently in different directions. Given the tight space constraints in a fob, is it possible that the antenna in the fob isn't an ideal omnidirectional antenna, and changing the fob's orientation WRT the car points a more powerful part of the fob's signal towards the car?

I should also point out that I have never been able to get this trick to work with my car (2004 VW Golf). My friend has done it with his first-production-year VW New Beetle, but the fob was different, so that may account for my failure. He has done it for me with his ~2003 Nissan Ultima and his 2005 Hyundai Tucson.

So, any explanations, or theories (pardon me, hypotheses)?

βPer

[Soapy Sam]

I recall a thread on this a couple of years ago. I cannot find it in "search". Anyone?

[Rolfe]

I do recall it being mentioned before. Don't remember where. My own remote control is broken at the moment, I'm having to turn the key in the lock, so I can't do any personal experiments.

Rolfe.

[Lisa Simpson]

It works on both my Toyota Sienna and my husband's Toyota Highlander. But I don't know why.

[Shrike]

Hi all.

I've seen this done on a BBC car show called Top Gear (www.bbc.co.uk/topgear/) one or two years ago, although there they aimed the key fob 'suicide style' at their temples.

Being an automotive engineer and a car nut myself, I went out and tried it myself. Along with some colleagues (enigneers and car nuts as well), we tried it on a parking field with a 1998 Alfa Romeo GTV and a 1999 Peugeot 306. Results for both cars was the same: holding the fob pressed against your skull would improve the range by several metres (metric only 'round here). :D
Of course, we also tried varying the positions of the fobs - and only aiming it at our temple, but the best result was when we pressed slightly against our temple. Thinking about it now, I guess we pressed the key against or temple (these are not the newest fobs without metal keys as used in the newest luxury cars).

Some older (or cheaper) models remote control use infra red, but not these. They are both radio remote controls.
When I'm back at work tomorrow I'll try and find out what frequency the use (I recall 133 MHz, but don't qoute me on this).
The only thing I can think of, is that the skull is working as some kind of amplifier, but my limited knowledge of radio transmitting and human biology prevents me from making any firm conclusions about this (maybe I'll try it with my cat next time.....).

I'm still quite curious at what causes this effect, so anybody who has an idea, please let me (or us) know.

[Blondin]

I can't find the instructions for mine but I remember it saying something about holding the remote at "chin-level" worked best. No mention of pressing it against any part of your anatomy.

The aerial is usually located at the top of the windscreen, just behind the rear-view mirror. My guess is that chin/head height just provides an optimal angle and position for the signal. If there are cars between you and your car then possibly the right height for the signal source might allow it to go through windows and reflect off car hoods. Too low and there's more metal between the remote and the aerial.

[Shrike]

The aerial is usually located at the top of the windscreen, just behind the rear-view mirror. My guess is that chin/head height just provides an optimal angle and position for the signal. If there are cars between you and your car then possibly the right height for the signal source might allow it to go through windows and reflect off car hoods. Too low and there's more metal between the remote and the aerial.

Correct.
But we tried that. Holding it next to our head, above our head, hip-height (is that a word?). Nothing. And the parking lot was clear - no cars but the two we were 'testing' on.
Against the head - bingo!

[TjW]

Originally posted by bPer
From yesterday's commentary:

quote:.... Warren also asks:

Another unexplained phenomenon: Do you know of anyone who can explain why I can hold my car's remote keyless entry fob to my chin and have its range tripled, or even quadrupled? Try it. Yeah, it works. Really!

There's the challenge for this week, folks. A cavity-resonance, antenna effect, or just what? Let us know your theories....!

I have a friend at work who claims this too. I've seen him demonstrate it several times. I have no idea what's going on, so I'd like to hear what people here have to say about it.

I will point out one thing I've observed when my friend has done the fob-to-chin trick. Normally, he (like most people I've observed) points his fob towards the car as he pushes the buttons. When he puts the fob to his chin, though, it is pointed upwards, and possibly rotated from its previous (unsuccessful) orientation. I've read just enough about antenna design to know that some antennas radiate differently in different directions. Given the tight space constraints in a fob, is it possible that the antenna in the fob isn't an ideal omnidirectional antenna, and changing the fob's orientation WRT the car points a more powerful part of the fob's signal towards the car?

I should also point out that I have never been able to get this trick to work with my car (2004 VW Golf). My friend has done it with his first-production-year VW New Beetle, but the fob was different, so that may account for my failure. He has done it for me with his ~2003 Nissan Ultima and his 2005 Hyundai Tucson.

So, any explanations, or theories (pardon me, hypotheses)?

βPer

I don't have any explanation for the range tripling or quadrupling, but if it's an RF fob, there's a couple of effects that would extend the range slightly:
Polarization: antennas couple best when they're oriented in the same direction. Depending on how the antenna is layed out on the fob pc board and the receiver,, rotating it up could increase the range. However, a receuver with a "diversity" receiver has antennas polarized in both directions, and switches between them, so you wouldn't see this effect on that kind of receiver.
Reflectivity: Putting something conductive (like a person) close behind an antenna can increase the directivity of the antenna.. If the fobs are in the 900MHz ISM band, then with the fob at your chin, your neck would be about a quarter-wavelength behind the fob. That's a pretty reasonable place for a reflector. Does the range go down if the person is facing away from the car?
Capacitive loading: Putting the antenna near a big bag of water (a person) could change the resonant frequency of the antenna a little. A better match to the output might allow a little more power out.

[MRC_Hans]

I can confirm that it works (although tripling the range is a bit optimistic). On my car, you need to have the metal key contact the skin somewhere on the head.

This also holds the clue to the effect: The key contains a small radio transmitter, the antenna of which couples to the metal key. I don't know which frequency band it operates in, but probably no higher than a couple of hundred megaherz, judging from the looks of the antenna coil inside it (a single PWB strip). For this frequency range, the coil and key metal constitute a woefully inefficient antenna, so anything that enhances this will greatly improve the range.

Touching the key to your head makes a nice big grounded antenna, your head and body being the ground part (standing outdoors, you body couples effectively to the ground in the RF range), and your arm forming a nice big loop.

Hans

[BillyJoe]

I'm in the unenviable position of having to trust others on this.
I do not have, and have never had, a car that uses a remote key.

:(

BJ

[MRC_Hans]

Originally posted by BillyJoe
I'm in the unenviable position of having to trust others on this.
I do not have, and have never had, a car that uses a remote key.

:(

BJ Means you have one thing less that can break :).

Hans

[BillyJoe]

Well, I have automatic gears, power-assisted steering,
air-conditioning and press-button wind-up windows.

One hot summers day I might get caught in first gear with
the air off and windows up pulling heavily on the steering.

:(

BillyJoe

[MRC_Hans]

Yeah. I have, in no particular order, power steering, remote key, air conditioning, push-button windows, electrically adjustable mirrors, electrical fold-in mirrors, electrically adjustable headlights, cruise control, open door alarms, etc. etc. I can't help wondering how long it will all keep working :(.

Hans

[treble_head]

it does not seem odd to me that the human body could act as an antenna. I have no scientific background, but I do know that when I hold the FM wire for my reciever on my sound sysem, it responds far more accurately than if I let it drop to the floor, or, indeed, set it on the counter behind the system at shoulder height.

I will not ever claim to know why, but it would seem that the human body can act as either a catylist or detractor for radio waves. I know, for example, that I can make the radio at work (from 50 feet away) start distorting by standing next to a certain wood-burning stove.

I have also tried the Key FOB trick, and it does seem to work better when holding it next to my head. I am as confused as anyone. Please, someone with enough knowledge, let us know. I figure we're all interested.

[Zep]

I'll toss in a few observations from experience that may help the discussion. I would be interested to see what real radio techies have to say too!

1) Remember the old rabbit-ears TV antennas? Remember how the reception was "good" while you adjusted them by hand, but went worse when you let go and backed away? Because your body was acting as an antenna extension for the TV (passively perhaps?).

Supposition: As said above, the human body can indeed act as a 1.83m long low-power antenna.

2) Having broken and vivisected a few of these little remote key thingies, I note they have freaking TINY little curved antenna arms - often less than 1cm per side. Surely this has an effect on effective transmission range?

Supposition: Even a low-power transmitter can cover quite long distances provided it has a reasonable antenna set.

Well??

[Soapy Sam]

Pioneer 10 comes to mind.

[gacrowell]

When I hold my key fob to my chin, I have to bend over to turn the key in the lock.

[jmercer]

That's still probably better than trying to use it while it's in your front pants pocket. :D

[treble_head]

yeah, well, when it's in my pocket it may not open my door more efficiently, but it sure is a lot more fun sometimes.

[BillyJoe]

I'm beginning to undertand the treble_head bit.