View Full Version : You know that thing with the key fobb
where you try to unlock a car in the car park from a hundred yards away and nothing happens but you press it to your head and it unlocks? How does that work then?
The Black Adder
21-12-2016, 19:25
I've seen people do that but I've personally never ever, ever needed to do it... or even thought to try it.
Does it really work?
Yes it does. It's always bugged me.
Infinitely Baffled
21-12-2016, 20:14
Yes, I know! It's really weird isn't it? I don't like it - it goes against the current of cool rationality (which is what I like to think is my natural stance - I've always been a bit up myself).
I still do it though!
IB.
archiesdad
21-12-2016, 21:34
Saw this tested on Top Gear once, didn't believe it worked so I tried it, and yes the car unlocked from further away, wondered if it has anything to do with the electrical impulses in the head?
Stryder5
21-12-2016, 21:44
The fob is higher so less interference from surrounding metal?
Firebottle
21-12-2016, 22:06
This works by improving the impedance match into the air from the transmitting antenna within the key fob.
Due to the restricted size of the normally printed circuit antenna, the radiating efficiency is very low.
The impedance of free space is 377 ohms and the impedance of the key fob antenna is likely well under the traditional RF impedance of 50 ohms.
The water content of the head acts as a transforming impedance to increase the radiated efficiency of the radio signal.
:D
alcarmichael
21-12-2016, 22:18
That's exactly what I was going to say but Alan beat me to it.
My car can open with the fob at around 100yards even without the head trick, I've not tested it that way,mmmm might try next time I've plenty room and report back lol.
I have this incredibly reliable technique, that I like to call "walking closer to the car". That is usually more successful if I include my head in the transitional movement.
The Black Adder
22-12-2016, 13:56
lol.. yes, cuts out walking another 10 paces. It's really no hardship to walk closer to the car...or in fact use a 'key' to open it. My car has a key... and so does my house.
jollyfix
22-12-2016, 14:15
For my fobb to work, it needs to be touching my van. Very much like the walkie talkies i had as a child at this time of year. You had to touch aerials for them to work. The car fobb on the other hand can work from the next village.
Not why youd want to anyways.. unless you have very long arms. I open mine when i get there tbh
This works by improving the impedance match into the air from the transmitting antenna within the key fob.
Due to the restricted size of the normally printed circuit antenna, the radiating efficiency is very low.
The impedance of free space is 377 ohms and the impedance of the key fob antenna is likely well under the traditional RF impedance of 50 ohms.
The water content of the head acts as a transforming impedance to increase the radiated efficiency of the radio signal.
:D
I'm so dumb I don't know if this is a serious explanation or a piss-take.
I see my explanation got short shrift anyway. Just a damned popularity contest ;)
Firebottle
22-12-2016, 15:53
It's serious Martin, honest :rolleyes:
Now I'm still not sure...
Audio Al
22-12-2016, 16:58
I was going to say it due to the increase in elevation , moving from hip height to head height allowing for the curvature of the earth
But Alan has blown me out of the water :lol:
I think there could be something in Alan's explanation. It's a bit like placing your portable radio near an upright steel stanchion - the reception is greatly improved.
Firebottle
22-12-2016, 18:49
It is true, I've done enough bu**ering about with antenna testing.
archiesdad
22-12-2016, 21:41
This works by improving the impedance match into the air from the transmitting antenna within the key fob.
Due to the restricted size of the normally printed circuit antenna, the radiating efficiency is very low.
The impedance of free space is 377 ohms and the impedance of the key fob antenna is likely well under the traditional RF impedance of 50 ohms.
The water content of the head acts as a transforming impedance to increase the radiated efficiency of the radio signal.
:D
It's gonna be one hell of an argument in the pub this weekend when I announce this "fact" HeeHee
The impedance of free space
Would make a good title for a prog instrumental.
jandl100
23-12-2016, 09:23
Well, this is a new one on me altogether.
Being a bit of a daft old bugger I quite often forget where I parked my car in a car park and use the key fob to light up the car lights so I can find it!
I'll now be able to do this over a longer range. :thumbsup:
Powered by vBulletin® Version 4.2.3 Copyright © 2026 vBulletin Solutions, Inc. All rights reserved.