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Why does holding a key fob to your head increase its range?

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Re: Why does holding a key fob to your head increase its range?

#111

Post by elzbardico »

ht85 wrote: post #92

From the top answer: > 1/2 m ≈ 1.5 ft Thanks US units for the quote of the day: "Meters are for waves, feet are for antennas"

Funny how everybody readily accepts the metric system for measuring radio wavelengths without complaints. Even the most hardcore traditionalist ham radio operator in America never complains about naming bands with meters.

Re: Why does holding a key fob to your head increase its range?

#112

Post by jimnotgym »

eps wrote: post #87
jvanderbot wrote: post #28

Earlier quoted context omitted.

vs holding it out at arms length but same height? Ground interference is a thing.

I can confirm that holding the remote next to the head doesn't work, but touching chin, temple or the back of the head does extend the range. This works not just with car remotes, but also with garage door openers.

Have you tried standing on one leg, and touching your nose with the free hand. Vast improvement over the amatuer technique

Re: Why does holding a key fob to your head increase its range?

#113

Post by b112 »

Johnythree wrote: post #42

A more likely theory is that the fob transmitter (and antenna) is tuned to put out max signal when near the body. This is it's normal use. If however you tested it with the fob somewhat isolated it would then be out of tune. eg in the factory it would be tuned at a set distance from a "dummy body". It's the same with a walkie-talkie radio. The antenna must be tuned when held in the hand, as your body provides the mis…

Or pointing it at your head, is the same as holding it up high in the air.

Re: Why does holding a key fob to your head increase its range?

#115

Post by johnny_canuck »

I used to use this trick when I worked as a photographer of used cars. You'd get some 10-20 fobs and be expected to walk a lot of ~300+ cars and take images of them. Holding the fob up to your chin was the trick to finding the right vehicle... assuming the battery wasn't dead.

I still use this trick today to find my car when I park somewhere I am unfamiliar with.

Re: Why does holding a key fob to your head increase its range?

#118

Post by peter_d_sherman »

Interesting!

>"This is a really interesting question. It turns out that your body is reasonably conductive (think salt water, more on that in the answer to this question), and that it can couple to RF sources capacitively."

Related: Capacative Coupling: https://en.wikipedia.org/wiki/Capacitive_coupling

Re: Why does holding a key fob to your head increase its range?

#119

Post by marcus0x62 »

When goofing off while tracing wires with a tone generator[0], we used to press the detector wand into our head, lick our finger tips, then run our fingers along the contacts on the 66 block[1] until we heard the warble from the tone generator.

0 - A troubleshooting and wire identification tool consisting of a battery-powered generator that produces a distinctive warbling sound and an inductive detector with a speaker that allows you to hear the warble when placed near the correct wire pair. Most look like this: https://www.grainger.com/product/EXTECH-Tone-and-Probe-Kit-4...

1 - a wiring terminal commonly used in the telephone system. https://en.wikipedia.org/wiki/66_block

Re: Why does holding a key fob to your head increase its range?

#120

Post by hulitu »

Johnythree wrote: post #42

A more likely theory is that the fob transmitter (and antenna) is tuned to put out max signal when near the body. This is it's normal use. If however you tested it with the fob somewhat isolated it would then be out of tune. eg in the factory it would be tuned at a set distance from a "dummy body". It's the same with a walkie-talkie radio. The antenna must be tuned when held in the hand, as your body provides the mis…

> A more likely theory is that the fob transmitter (and antenna) is tuned to put out max signal when near the body. This is it's normal use.

This is true.

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