Car Immobiliser Physics Question

Do you need to point the remote at the car (IR) or not (RF)?

For sleep see : http://en.wikipedia.org/wiki/Infrared

The remote seems to be uni-directional - don't need to point it at the car.

Omni-directional.

I was wondering what the red LED on my Fob is for. Mine doesn't seem to do anything except blink corresponding to the lock activity.

oops - yeah thats the one! Omni. Thanks.

the LED is what initially made me think it was IR, but i guess its just for aesthetic effect.

IR is not visible and this little bugger is visible red light.

The key pops out like a switchblade too.

I would be guessing that because you have elevated the reomte to the height of your forhead, rather than waist height, you have increased the intensity or range of the signal, much like a radio tower does. Next time try the experiment with the immobiliser inline with your head, but in an outstretched arm, the result should be the same. However if this is not the case then the signal is being reflected by your head; to test this, replace your head with a block of (timer, brick, plastic bucket of water) on a stand and try again.

The answer will be in the results.

Have fun!

Sounds like a study for MIT: The reflectivity of cranial structures...and their replacements. I wonder if our guest has tried this without his foil beany (to prevent the government from reading his brainwaves or controlling his mind, of course )?

I saw this explained once (I ferget where). Pointing the 'thingy' in the opposite direction, or 'banking' it off an object spreads the beam out for better coverage. I use the same effect for the TV remote, pointing it at the window behind me, rather than trying to find the sensor with a beam that is too tight.

Hello Tippycanoe,

Then when it 'bounces' off something and is reflected it is a little like a 'dish' antenna, as you would use for reception of TV?

The added elevation provides a more unobstructed path for the RF to reach your car.

Head high versus pocket high.

Just to add more confusion to this blog:- I had a colleague who when he needed distance with his key fob, he opened his mouth wide in the direction of his car and operated the fob when it was in the middle between his teeth. As a sort of reflector.....it actually worked too, I was stunned......at the same height, with mouth closed, it did not funtion......

When visiting my wife on the 6th floor of a hospital some years ago, I realized I had not locked the car door and it was about half a mile away, well out of normal range (VW have/had short range only like 25-35 meters...). It worked fine and locked all the doors.....I could even see the light signal well as it was night!!!

I checked it several times just to make sure that it ONLY happened when I used my fob.....and it was not someone else's car.....with their fob that just happened to be there nearby....and the car was locked when I got back to it...

My Wife's VW will lock itself after a period of time. Don't ever leave your keys in there with the door closed or it will lock you out. Personally I'd prefer it didn't do this just far this reason.
But her key fob has a range of about 100' if no large obstructions are in the way.

I had a hire Passat that would lock all doors if the engine was running and all doors were closed....it forgot to check if anyone was actually sitting in it, the sensors for the airbag in the seats should have been checked for a human body, but were not.

That was a Passat from 2003 or 4 if I remember correctly...since then I always open a window first on all makes....

My 2004 Passat, left unlocked, has never locked itself, except a time or two when I moved in such a way that something else in my pocket pressed the lock button on the fob in my pocket.

I did once open the trunk in the already locked car, and closed the trunk with the fob inside. The little beep told me my keys were then securely locked in the trunk. I was lucky that day - only hours earlier I had given my best friend my spare key, so he came and unlocked it for me. I have been pretty careful since then...

Have you tried closing all the doors with the engine running (open a window first or have the spare key handy!) ? The problem comes when all doors are already closed and then you close the tailgate.....

This was the scenario that left me waiting in a no parking (0800 to 1800 on workdays) zone from 0745 till 1000 when the ADAC came and forced the door for me!!

Maybe an update has fixed that problem already on all cars that get maintained by VW...

In respone to post #8 and #14, spreading the signal (bouncing it off another surface) will actually decrease the range rather than increasing it.

I would guess that holding the remote up to your body would create a ground-plane for the device's antenna effectively increasing the gain (and range) of the transmitted signal.

Take a ohm meter (turn up to whatever K). Wet your left and right thumb and index finger, hold either end (+ or -) and squeeze. If there is no reading check the battery. 1.5 volts WILL pass through you. Your body can be used as receiver because of the "water tower" that we are. As my wife walks by the old FM radio in the race shop the reception becomes clearer, if you hold the antenna on the radio reception is better......To the point, you absorb microwaves and radio waves and amplify that signal by your mass receptiveness. Probably the sweat on you hand was the conductor. Try using a glove and see if there is a noticable dif. Whew I hope this doesn't cause nightmares but lots of us used to here short wave through our fillings.

In answer to why the rf transmitter works over a longer range when held agains to head, the bone mass in you head acts as a amplifer, amplifing the signal strenght, sleep well.

Also i understand but have not tried it, if you lock you keys in you car or are locked out of your house you could phone your freind that also has the spare remote and ask them to hold it up to the phone and press the unlock button, your door should then unlock.

"In answer to why the rf transmitter works over a longer range when held agains to head, the bone mass in you head acts as a amplifer, amplifing the signal strenght, sleep well."

An amplifier requires a source of energy, and a means of using that energy to increase the amplitude of a signal. Bone mass has neither, so I can't accept your answer.

Your head is a fairly decent conductor, and as such could act as a reflector, which is what a ground plane does. That lends credence to TS and BB's first line.

Hello dkwarner,

Hope you are well?

Just a word or three to say I appreciate the mention in one of your posts, with ref' to "Ground Plain Antenna".

Take care my friend

I must try it some time, best regards

Please post your results here! Thanks!

How does that work??? My fob is a RF transmitter...a phone cannot send RF, it has problems enough sometimes with AF!!!!!

Hello Andy,

With ref' to your "a phone cannot sent RF"..................

Check this out. I think you will see that MOBILE phones can transmit RF in the Microwave range?

Have a look and tell me what you think please. because I think I am right, but it is sort of arguable................ on the exact detail and way it sends.

Interesting topic don't you think?

http://www.google.com/search?hl=en&client=safari&rls=en-us&ei=DzlPSsnUCterjAeVsKDUBw&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=mobile+phones+and+the+radio+frequency&spell=1

But NOT via a microphone!!!!!!!!!!

Thats AF......and not even full range AF either.......

Andy,

How about two cans connected by a waxed string?

Improvement?

Jon

....as long as two empty baked bean tins are also placed at each end to work as a mike/loudspeaker, it should work (and as long as the string does not exceed 10 meters!)

You could change that to:"Mobile phones DO transmit RF in the Microwave range!" I believe all the bands mentioned by kudukdweller9 are considered to be microwaves. However, the power output of a cellphone is around four orders of magnitude smaller (1/10,000) than that of the common microwave oven, and the cellphone must be pretty much omnidirectional, so only a tiny fraction of that already low output ever enters your body. In the oven, it is sealed so the waves are forced to bounce around until they have passed through the food enough times to be absorbed by the food.

I believe there are other reasons to limit the use of cellphones of much greater significance (both medical and social) than the radiation hazard.

Hi Andy,

"A phone cannot send RF, it has problems enough sometimes with AF!"

Humor!

Sometimes it seems that way. Cell phones operate on the 850 MHz, 900 MHz, 1.8 GHz and 1.9 GHz bands.

My phone can use GSM and CDMA and any of those bands. I no longer have a "do nothing phone" when I travel.

I get a kick out of seeing movies with a person holding a boat anchor with a long wire sticking out of it, up to his ear and talking to it.

Jon

But a Fob uses RF at some frequency....it cannot send via a mike.....thats AF only.....

I would say your body is acting as a ground plain antenna.

The key fob does not need to use as much power to receive (and perhaps also send) signals, as it would at arms length, if you hold it against your body, which I think you will find, effectively acts as an Antenna.

In doing this your body is a huge EM/RF receiver compared to the tiny Antenna of the key fob, so it may 'receive' a better signal from the car and transfers it to the key fob.

I think the same thing may happen to the key fob to car direction, but am not certain of that. hence less battery power. And longer battery life, because if it only happens 'one way', IE: with your body receiving the signal, it means you use roughly half as much battery power. If, as I suspect, your body also helps to send the signal from the key fob to the car, then you can expect a substantial saving in batteries.

That is my thoughts on the subject without any research yet.

I think your first statement is probably correct, although in the US we call it a ground plane (as in flat surface).

Unless I am badly mistaken, remotes (including car fobs) do not receive any signals from anything other than the buttons. They only transmit pulses. Anything that can increase the efficiency of that sending will increase the range. An appropriately placed reflector, such as your head, could do that.

I suspect the increased 'visibility' due to holding the fob higher is the more important factor, as illustrated by Andy's locking the car from a very long distance, but also a large height (and presumably line-of sight to the car).

Hello dkwarner,

Hey, sorry for the miss spelling on "ground plane"

/'plain' < wrong!

Hello Guest,

On checking it does seem the human or presumably any living body does act as an Antenna, for all kinds of EM and RF frequencies.

The search page below has a good selection of titles on this subject. I am telling you the search page but have not had time to read much, but it seems from the subjects and rėsumės the body does act like an antenna.

http://www.google.com/search?client=safari&rls=en-us&q=human+body+acts+as+an+antenna&ie=UTF-8&oe=UTF-8 .

You need to read further in several of the references cited...

Yes, I have used my body to modify reception of radio signals many times, both intentionally and otherwise; both improving and degrading signals.

Anyone who has any knowledge of antennas knows that the length and orientation of the antenna is very important. The human body is of a size to act as an antenna for signals in the range of roughly 50-150Mhz, which includes the FM and VHF bands. At higher frequencies like those used in RF remotes and cell phones, the wavelength is much too small. In that case the body does not act as an antenna, but rather as a reflector. For lower frequencies, the body is to small to be an efficient antenna, but can act as a ground.

At least a few of the references on that page of links refer to such things as yoga positions, which I suspect have a lot to do with blood circulation or the lack thereof, and very little to do with wave reception and/or transmission.

On the other hand, I do believe I have experienced Extra Sensory Communication a few times. This would imply that the human brain is capable of sending and receiving signals over large distances, under certain circumstances. I can't imagine how this could be achieved, other than by EM waves, and that would require electrical oscillations (which sounds possible in a brain), and some form of 'antenna', which is a little harder, since your skull and scalp would seem to be a Farraday cage for the brain...

Hello dkwarner ....again!

With regard to the length or synchronous tuning of a wire, and the orientation, to make it an antenna............ I have used several 'straight wire' antenna's, and found the reception was great in the direction of the 'poles' of the wire. But dropped off dramatically at 'right angles' to it.

I used to have a TX License but, have forgotten a lot of it now. Can't forget the 'basics' though!

One of the antenna's I used was a North/South direction so could pick up Brazil and northern Europe very well. I think a 'half-wave' antenna for shortwave is 132', (40.23 Meters) Approx'.

If anyone wants to know about this I have a site I know of but, it will be off topic, so tell me and I will publish it.

Thanks for the search string, BabyBear. It was some interesting reading. Some results were in layman's terms and others were an introduction in wave propagation. Don't you just love Google?

Hello tropicalspeed,

Thanks for the reply post my friend.

Yeah, Google either gives it all or nothing sorta? I did not know how far anyone was into the radio frequency spectrum so, thought I would just leave the page address as there was and is something for everyone, from novice to Masters!

I just find it so interesting. There is too much in it for me to take it in its entirety but, I use it and know when I am using it what the outcome will be when I try something etc. Kinda got a little lost there sorry. Thanks anyway!

Hello Guest,

This is an interesting thread!............

Why do you not join? We are friendly with good mannered members, and 'admin' jump on anything that may not be good or is way off topic. There is some very clever people here many with Masters Degrees etc. Join!

and here I am - first post!

woo!

Welcome!

Welcome...

Yeah. And if you point yer foot at the radio aerial it picks up BBC2. Pull the other one. It's got bells on. <Splutter>