The same reason your phone speaker gets louder when you put it on the table.
Why does holding a key fob to your head increase its range?
71–80 of 161 posts
Re: Why does holding a key fob to your head increase its range?
#72In the movie LalaLand, they mention that this is dangerous (causing diseases). Is that true?
Should we worry about a radio transmission powered by a 3 volt battery while taking on our phone?
Depends. There is lots of irrational fear with this and as far as I know, no solid proof for harm, but there is extra electricity flowing in your head, because of the transmission of your phone. I don't like talking on the phone that much anyway, so I do not care so much, but if I would talk for hours, I would use a headset (also for ergonomic reasons).
Re: Why does holding a key fob to your head increase its range?
#73Not sure I agree with the cavity theory. I suspect it’s you, you big ole bag of salt water, acting as a capacitive ground plane for the antenna. It’s like mounting a ham or CB antenna on a car and having the metal of the car not be in direct contact with the ground, but it acts as a capacitive ground plane. You can do something similar with a vertical antenna using ground radials in a star pattern on the ground.
I think this is the real answer.
Re: Why does holding a key fob to your head increase its range?
#74The answer posted with all the experiments is conducted with a 2009 GTI, which reminds me of my first car, a Jetta from a generation before that. Its manual included this helpful illustration of the full expected range of the remote: https://imgur.com/a/1Pdfyg4 Yes, apparently they were only willing to promise it would work within about arm's length of the car! It wasn't that bad, but also it wasn't a heck of a lot b…
My first thought was "I wonder if the car is to scale or the fob"
Re: Why does holding a key fob to your head increase its range?
#75[dead]
Re: Why does holding a key fob to your head increase its range?
#76Earlier quoted context omitted.
Even simpler, tune in an FM radio and move your hand near the antenna. It will sound better or worse depending on your hand position and how close it is to the antenna.
Back in the early 00's when we still had analogue VHF TV signals, we wanted to watch the football world cup at school. Of course there was no cable or anything at the school and no VHF antenna and streaming was not a possibility yet so we had to be creative. We found an antenna cable and tried to manipulate the cable and use whatever as an antenna. We tried the sheet metal roofing, but that didn't work very well, we…
Fond memories here of watching Babylon 5 on a Performa 5300 with an Apple TV Tuner Card. There was no antenna to the room with the computer, but I found that I was able to get an acceptable picture by holding the coax cable attached to the antenna input in the right way while keeping one hand attached to the central heating radiator...
Re: Why does holding a key fob to your head increase its range?
#77Earlier quoted context omitted.
Microwave RF that is somewhat directional behaves a lot like laser light. If you were to step into the beam carried by a waveguide for something like a powerful TV transmitter, it will cook you through like a death ray out of science fiction. Fortunately it's not actually collimated, so just a few feet away the energy is barely enough to cook your retinas faster than your blood supply can cool them (which can cause b…
> Microwave RF that is somewhat directional behaves a lot like laser light. While fob frequency is microwave, isn't it also much lower energy compared to, say a microwave oven, powered by mains power to cook food? And also the fob operating in the low 100s of Mhz, not GHz, wouldn't that make it less dangerous?
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Re: Why does holding a key fob to your head increase its range?
#78A 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…
Even simpler, tune in an FM radio and move your hand near the antenna. It will sound better or worse depending on your hand position and how close it is to the antenna.
Reminded me of discovering this when I was a kid and thought I was magic. I had forgotten about that.
Re: Why does holding a key fob to your head increase its range?
#79A 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…
More likely than what? SE comments provide at least three distinct theories. IMO this one (also provided in the comments) seems fairly conclusive https://www.remcom.com/examples/keyless-entry.html
Re: Why does holding a key fob to your head increase its range?
#80An explanation I read somewhere is that the radio waves reflect from the inside of your skull, the curvature acts as a parabolic antenna.