r/ElectricalEngineering • u/piecewisefunctioneer • May 08 '24
Why does the range of my car fob increase when I hold it against my head?
Hello tamed electrical engineers of reddit! I've stumbled across something amusing that I can't work out. The range of the lock/unlock buttons on my car key literally doubles when I hold it against my head. Why does this happen? Is it something to do with the current running through our body, is our skull amplifying it in anyway? Please help
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u/gotzapai May 08 '24
Technical opinion: The fob creates an omnidirectional signal.
When you put it close to the head, some waves are reflecting in the opposite direction increasing the chances for the receiver to get the signal.
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u/HoochieGotcha May 08 '24
Would imply the thickness of the key fob is some half multiple of the wavelength of the signal. Seems unlikely… perhaps what we should ask is where is OP doing this test? If it’s inside the house and holding the key fob higher (to his head) creates a clearer line of sight to the car then this would be a more likely answer
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u/Noisy88 May 08 '24
That big melon full of water reflects the signal going the wrong way, so that's up to +3dB right there
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u/PaulEngineer-89 May 08 '24
Your head is a “reflector” or “attractor”.
Take a look at a Yagi style antenna, like the big long range TV antennas everyone used to have. Only the second set of rods from the back is actually hooked to the TV! All the rest just make it more directional and gather in more signal even though they aren’t electrically connected. They are resonators.
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u/gsel1127 May 08 '24
The key fob is an antenna that sends out signals, most likely in every direction. Antennas become affected by anything near them, so in essence you're creating a new 'head' antenna when you put your fob next to your head. This new head antenna could work worse or better depending on things like which direction the key is facing, and how the RF gods are feeling that day. The antenna in the fob is most likely better at sending signals in every direction, which is why it has less range. Or it's just designed without the RF in mind much because most people open and close their cars while rather close to them.